Oracle高级查询之OVER (PARTITION BY ..)
<p><em style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; white-space: normal; background-color: rgb(255, 255, 255);">注：标题中的红色order by是说明在使用该方法的时候必须要带上order by。</em><span style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; background-color: rgb(255, 255, 255);"></span></p><p style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; white-space: normal; background-color: rgb(255, 255, 255);"><strong><span style="font-size: 16px;">一、rank()/dense_rank() over(partition by ...<span style="color: rgb(255, 0, 0);">order by ...</span>)</span></strong></p><p><span style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; background-color: rgb(255, 255, 255);">现在客户有这样一个需求，查询每个部门工资最高的雇员的信息，相信有一定oracle应用知识的同学都能写出下面的SQL语句：</span><br/></p><p><strong></strong> <a href="http://blog.csdn.net/fu0208/article/details/7179001#" class="ViewSource" title="view plain" target="_blank" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url(http://static.blog.csdn.net/scripts/SyntaxHighlighter/styles/images/default/ico_plain.gif); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: 0% 0%; background-repeat: no-repeat;">view plain</a> <a href="http://blog.csdn.net/fu0208/article/details/7179001#" class="CopyToClipboard" title="copy" target="_blank" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url(http://static.blog.csdn.net/scripts/SyntaxHighlighter/styles/images/default/ico_copy.gif); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: 0% 0%; background-repeat: no-repeat;">copy</a></p><ol class="dp-sql list-paddingleft-2" style="padding: 0px; border: none; color: rgb(92, 92, 92); margin-bottom: 1px !important; margin-left: 45px !important; background-color: rgb(255, 255, 255);"><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">select</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.ename, e.job, e.sal, e.deptno </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">from</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> scott.emp e, </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> (<span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">select</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.deptno, </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">max</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">(e.sal) sal </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">from</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> scott.emp e </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">group</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">by</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.deptno) me </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">where</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.deptno = me.deptno </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="op" style="margin: 0px; padding: 0px; border: none; color: rgb(128, 128, 128); background-color: inherit;">and</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.sal = me.sal; </span></span></p></li></ol><p><span style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; background-color: rgb(255, 255, 255);">在满足客户需求的同时，大家应该习惯性的思考一下是否还有别的方法。这个是肯定的，就是使用本小节标题中rank() over(partition by...)或dense_rank() over(partition by...)语法，SQL分别如下：</span></p><p><strong></strong> <a href="http://blog.csdn.net/fu0208/article/details/7179001#" class="ViewSource" title="view plain" target="_blank" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url(http://static.blog.csdn.net/scripts/SyntaxHighlighter/styles/images/default/ico_plain.gif); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: 0% 0%; background-repeat: no-repeat;">view plain</a> <a href="http://blog.csdn.net/fu0208/article/details/7179001#" class="CopyToClipboard" title="copy" target="_blank" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url(http://static.blog.csdn.net/scripts/SyntaxHighlighter/styles/images/default/ico_copy.gif); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: 0% 0%; background-repeat: no-repeat;">copy</a></p><ol class="dp-sql list-paddingleft-2" style="padding: 0px; border: none; color: rgb(92, 92, 92); margin-bottom: 1px !important; margin-left: 45px !important; background-color: rgb(255, 255, 255);"><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">select</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.ename, e.job, e.sal, e.deptno </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">from</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> (</span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">select</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.ename, </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> e.job, </span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> e.sal, </span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> e.deptno, </span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> rank() over(partition <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">by</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.deptno </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">order</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">by</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.sal </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">desc</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">) rank </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">from</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> scott.emp e) e </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">where</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.rank = 1; </span></span></p></li></ol><p><strong></strong> <a href="http://blog.csdn.net/fu0208/article/details/7179001#" class="ViewSource" title="view plain" target="_blank" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url(http://static.blog.csdn.net/scripts/SyntaxHighlighter/styles/images/default/ico_plain.gif); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: 0% 0%; background-repeat: no-repeat;">view plain</a> <a href="http://blog.csdn.net/fu0208/article/details/7179001#" class="CopyToClipboard" title="copy" target="_blank" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url(http://static.blog.csdn.net/scripts/SyntaxHighlighter/styles/images/default/ico_copy.gif); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: 0% 0%; background-repeat: no-repeat;">copy</a></p><ol class="dp-sql list-paddingleft-2" style="padding: 0px; border: none; color: rgb(92, 92, 92); margin-bottom: 1px !important; margin-left: 45px !important; background-color: rgb(255, 255, 255);"><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">select</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.ename, e.job, e.sal, e.deptno </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">from</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> (</span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">select</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.ename, </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> e.job, </span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> e.sal, </span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> e.deptno, </span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> dense_rank() over(partition <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">by</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.deptno </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">order</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">by</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.sal </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">desc</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">) rank </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">from</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> scott.emp e) e </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">where</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.rank = 1; </span></span></p></li></ol><p><span style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; background-color: rgb(255, 255, 255);">为什么会得出跟上面的语句一样的结果呢？这里补充讲解一下rank()/dense_rank() over(partition by e.deptno order by e.sal desc)语法。</span><br/><strong style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; white-space: normal; background-color: rgb(255, 255, 255);">over: </strong><span style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; background-color: rgb(255, 255, 255);">在什么条件之上。</span><br/><strong style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; white-space: normal; background-color: rgb(255, 255, 255);">partition by e.deptno: </strong><span style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; background-color: rgb(255, 255, 255);">按部门编号划分（分区）。</span><br/><strong style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; white-space: normal; background-color: rgb(255, 255, 255);">order by e.sal desc: </strong><span style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; background-color: rgb(255, 255, 255);">按工资从高到低排序（使用rank()/dense_rank() 时，必须要带order by否则非法）</span><br/><strong style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; white-space: normal; background-color: rgb(255, 255, 255);">rank()/dense_rank(): </strong><span style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; background-color: rgb(255, 255, 255);">分级</span><br/><span style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; background-color: rgb(255, 255, 255);">整个语句的意思就是：在按部门划分的基础上，按工资从高到低对雇员进行分级，“级别”由从小到大的数字表示（最小值一定为1）。 </span></p><p style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; white-space: normal; background-color: rgb(255, 255, 255);">那么rank()和dense_rank()有什么区别呢？<br/><strong>rank(): </strong>跳跃排序，如果有两个第一级时，接下来就是第三级。<br/><strong>dense_rank(): </strong>连续排序，如果有两个第一级时，接下来仍然是第二级。</p><p style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; white-space: normal; background-color: rgb(255, 255, 255);"><em>小作业：查询部门最低工资的雇员信息。</em></p><p style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; white-space: normal; background-color: rgb(255, 255, 255);"><strong><span style="font-size: 16px;">二、min()/max() over(partition by ...)</span></strong></p><p style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; white-space: normal; background-color: rgb(255, 255, 255);">现在我们已经查询得到了部门最高/最低工资，客户需求又来了，查询雇员信息的同时算出雇员工资与部门最高/最低工资的差额。这个还是比较简单，在第一节的groupby语句的基础上进行修改如下：<br/></p><p><strong></strong> <a href="http://blog.csdn.net/fu0208/article/details/7179001#" class="ViewSource" title="view plain" target="_blank" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url(http://static.blog.csdn.net/scripts/SyntaxHighlighter/styles/images/default/ico_plain.gif); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: 0% 0%; background-repeat: no-repeat;">view plain</a> <a href="http://blog.csdn.net/fu0208/article/details/7179001#" class="CopyToClipboard" title="copy" target="_blank" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url(http://static.blog.csdn.net/scripts/SyntaxHighlighter/styles/images/default/ico_copy.gif); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: 0% 0%; background-repeat: no-repeat;">copy</a></p><ol class="dp-sql list-paddingleft-2" style="padding: 0px; border: none; color: rgb(92, 92, 92); margin-bottom: 1px !important; margin-left: 45px !important; background-color: rgb(255, 255, 255);"><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">select</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.ename, </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> e.job, </span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> e.sal, </span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> e.deptno, </span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> e.sal - me.min_sal diff_min_sal, </span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> me.max_sal - e.sal diff_max_sal </span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">from</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> scott.emp e, </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> (<span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">select</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.deptno, </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">min</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">(e.sal) min_sal, </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">max</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">(e.sal) max_sal </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">from</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> scott.emp e </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">group</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">by</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.deptno) me </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">where</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.deptno = me.deptno </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">order</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">by</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.deptno, e.sal; </span></span></p></li></ol><p><span style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; background-color: rgb(255, 255, 255);">上面我们用到了min()和max()，前者求最小值，后者求最大值。如果这两个方法配合over(partition by ...)使用会是什么效果呢？大家看看下面的SQL语句：</span></p><p><strong></strong> <a href="http://blog.csdn.net/fu0208/article/details/7179001#" class="ViewSource" title="view plain" target="_blank" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url(http://static.blog.csdn.net/scripts/SyntaxHighlighter/styles/images/default/ico_plain.gif); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: 0% 0%; background-repeat: no-repeat;">view plain</a> <a href="http://blog.csdn.net/fu0208/article/details/7179001#" class="CopyToClipboard" title="copy" target="_blank" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url(http://static.blog.csdn.net/scripts/SyntaxHighlighter/styles/images/default/ico_copy.gif); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: 0% 0%; background-repeat: no-repeat;">copy</a></p><ol class="dp-sql list-paddingleft-2" style="padding: 0px; border: none; color: rgb(92, 92, 92); margin-bottom: 1px !important; margin-left: 45px !important; background-color: rgb(255, 255, 255);"><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">select</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.ename, </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> e.job, </span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> e.sal, </span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> e.deptno, </span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> nvl(e.sal - <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">min</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">(e.sal) over(partition </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">by</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.deptno), 0) diff_min_sal, </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> nvl(<span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">max</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">(e.sal) over(partition </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">by</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.deptno) - e.sal, 0) diff_max_sal </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">from</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> scott.emp e; </span></span></p></li></ol><p><span style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; background-color: rgb(255, 255, 255);">这两个语句的查询结果是一样的，大家可以看到min()和max()实际上求的还是最小值和最大值，只不过是在partition by分区基础上的。</span><br/></p><p style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; white-space: normal; background-color: rgb(255, 255, 255);"><em>小作业：如果在本例中加上order by，会得到什么结果呢？</em></p><p style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; white-space: normal; background-color: rgb(255, 255, 255);"><strong><span style="font-size: 16px;">三、lead()/lag() over(partition by ... order by ...)</span></strong><br/></p><p style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; white-space: normal; background-color: rgb(255, 255, 255);">中国人爱攀比，好面子，闻名世界。客户更是好这一口，在和最高/最低工资比较完之后还觉得不过瘾，这次就提出了一个比较变态的需求，计算个人工资与比自己高一位/低一位工资的差额。这个需求确实让我很是为难，在groupby语句中不知道应该怎么去实现。不过。。。。现在我们有了over(partition by ...)，一切看起来是那么的简单。如下：</p><p><strong></strong> <a href="http://blog.csdn.net/fu0208/article/details/7179001#" class="ViewSource" title="view plain" target="_blank" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url(http://static.blog.csdn.net/scripts/SyntaxHighlighter/styles/images/default/ico_plain.gif); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: 0% 0%; background-repeat: no-repeat;">view plain</a> <a href="http://blog.csdn.net/fu0208/article/details/7179001#" class="CopyToClipboard" title="copy" target="_blank" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url(http://static.blog.csdn.net/scripts/SyntaxHighlighter/styles/images/default/ico_copy.gif); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: 0% 0%; background-repeat: no-repeat;">copy</a></p><ol class="dp-sql list-paddingleft-2" style="padding: 0px; border: none; color: rgb(92, 92, 92); margin-bottom: 1px !important; margin-left: 45px !important; background-color: rgb(255, 255, 255);"><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">select</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.ename, </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> e.job, </span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> e.sal, </span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> e.deptno, </span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> lead(e.sal, 1, 0) over(partition <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">by</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.deptno </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">order</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">by</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.sal) lead_sal, </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> lag(e.sal, 1, 0) over(partition <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">by</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.deptno </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">order</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">by</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.sal) lag_sal, </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> nvl(lead(e.sal) over(partition <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">by</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.deptno </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">order</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">by</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.sal) - e.sal, </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> 0) diff_lead_sal, </span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> nvl(e.sal - lag(e.sal) over(partition <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">by</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.deptno </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">order</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">by</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.sal), 0) diff_lag_sal </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">from</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> scott.emp e; </span></span></p></li></ol><p><span style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; background-color: rgb(255, 255, 255);">看了上面的语句后，大家是否也会觉得虚惊一场呢（惊出一身冷汗后突然鸡冻起来，这样容易感冒）？我们还是来讲解一下上面用到的两个新方法吧。</span><br/><strong style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; white-space: normal; background-color: rgb(255, 255, 255);">lead(列名,n,m): </strong><span style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; background-color: rgb(255, 255, 255);">当前记录后面第n行记录的<列名>的值，没有则默认值为m；如果不带参数n,m，则查找当前记录后面第一行的记录<列名>的值，没有则默认值为null。</span><br/><strong style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; white-space: normal; background-color: rgb(255, 255, 255);">lag(列名,n,m): </strong><span style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; background-color: rgb(255, 255, 255);">当前记录前面第n行记录的<列名>的值，没有则默认值为m；如果不带参数n,m，则查找当前记录前面第一行的记录<列名>的值，没有则默认值为null。</span></p><p style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; white-space: normal; background-color: rgb(255, 255, 255);">下面再列举一些常用的方法在该语法中的应用（<em><strong>注：带order by子句的方法说明在使用该方法的时候必须要带order by</strong></em>）：</p><p><strong></strong> <a href="http://blog.csdn.net/fu0208/article/details/7179001#" class="ViewSource" title="view plain" target="_blank" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url(http://static.blog.csdn.net/scripts/SyntaxHighlighter/styles/images/default/ico_plain.gif); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: 0% 0%; background-repeat: no-repeat;">view plain</a> <a href="http://blog.csdn.net/fu0208/article/details/7179001#" class="CopyToClipboard" title="copy" target="_blank" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url(http://static.blog.csdn.net/scripts/SyntaxHighlighter/styles/images/default/ico_copy.gif); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: 0% 0%; background-repeat: no-repeat;">copy</a></p><ol class="dp-sql list-paddingleft-2" style="padding: 0px; border: none; color: rgb(92, 92, 92); margin-bottom: 1px !important; margin-left: 45px !important; background-color: rgb(255, 255, 255);"><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">select</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.ename, </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> e.job, </span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> e.sal, </span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> e.deptno, </span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> first_value(e.sal) over(partition <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">by</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.deptno) first_sal, </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> last_value(e.sal) over(partition <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">by</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.deptno) last_sal, </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="func" style="margin: 0px; padding: 0px; border: none; color: rgb(255, 20, 147); background-color: inherit;">sum</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">(e.sal) over(partition </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">by</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.deptno) sum_sal, </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="func" style="margin: 0px; padding: 0px; border: none; color: rgb(255, 20, 147); background-color: inherit;">avg</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">(e.sal) over(partition </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">by</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.deptno) avg_sal, </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="func" style="margin: 0px; padding: 0px; border: none; color: rgb(255, 20, 147); background-color: inherit;">count</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">(e.sal) over(partition </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">by</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.deptno) count_num, </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> row_number() over(partition <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">by</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.deptno </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">order</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">by</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> e.sal) row_num </span></span></p></li><li><p><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">from</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> scott.emp e; </span></span></p></li></ol><p><br/><strong style="color: rgb(51, 51, 51); font-family: Arial; font-size: 14px; line-height: 26px; white-space: normal; background-color: rgb(255, 255, 255);"><span style="color: rgb(255, 102, 102);">重要提示：大家在读完本片文章之后可能会有点误解，就是OVER (PARTITION BY ..)比GROUP BY更好，实际并非如此，前者不可能替代后者，而且在执行效率上前者也没有后者高，只是前者提供了更多的功能而已，所以希望大家在使用中要根据需求情况进行选择。</span></strong></p><p><br/></p>
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