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[数据库]Oracle函数之LISTAGG


最近在学习的过程中,发现一个挺有意思的函数,它可实现对列值的拼接。下面我们来看看其具体用法。

用法:

对其作用,官方文档的解释如下:

For a specified measure, LISTAGG orders data within each group specified in the ORDER BY clause and then concatenates the values of the measure column.

即在每个分组内,LISTAGG根据order by子句对列植进行排序,将排序后的结果拼接起来。

measure_expr:可以是任何基于列的表达式。

delimiter:分隔符,默认为NUL

order_by_clause:order by子句决定了列值被拼接的顺序。

通过该用法,可以看出LISTAGG函数不仅可作为一个普通函数使用,也可作为分析函数。

order_by_clause和query_partition_clause的用法如下:

下面对该函数进行举例说明:

普通函数,对工资进行排序,用逗号进行拼接。

SQL> select listagg(ename,',')within group(order by sal)name from emp;NAME----------------------------------------------------------------------------------------------------SMITH,JAMES,ADAMS,MARTIN,WARD,MILLER,TURNER,ALLEN,CLARK,BLAKE,JONES,FORD,SCOTT,KING

分组函数:

SQL> select deptno,listagg(ename,',')within group(order by sal)name from emp group by deptno;  DEPTNO NAME---------- ----------------------------------------------------------------------------------------------------  10 MILLER,CLARK,KING  20 SMITH,ADAMS,JONES,FORD,SCOTT  30 JAMES,MARTIN,WARD,TURNER,ALLEN,BLAKE

分析函数:

SQL> select deptno,ename,sal,listagg(ename,',')within group(order by sal)over(partition by deptno)name from emp;  DEPTNO ENAME       SAL NAME---------- ---------- ---------- ----------------------------------------    10 MILLER      1300 MILLER,CLARK,KING    10 CLARK      2450 MILLER,CLARK,KING    10 KING       5000 MILLER,CLARK,KING    20 SMITH       800 SMITH,ADAMS,JONES,SCOTT,FORD    20 ADAMS      1100 SMITH,ADAMS,JONES,SCOTT,FORD    20 JONES      2975 SMITH,ADAMS,JONES,SCOTT,FORD    20 SCOTT      3000 SMITH,ADAMS,JONES,SCOTT,FORD    20 FORD       3000 SMITH,ADAMS,JONES,SCOTT,FORD    30 JAMES       950 JAMES,MARTIN,WARD,TURNER,ALLEN,BLAKE    30 MARTIN      1250 JAMES,MARTIN,WARD,TURNER,ALLEN,BLAKE    30 WARD       1250 JAMES,MARTIN,WARD,TURNER,ALLEN,BLAKE    30 TURNER      1500 JAMES,MARTIN,WARD,TURNER,ALLEN,BLAKE    30 ALLEN      1600 JAMES,MARTIN,WARD,TURNER,ALLEN,BLAKE    30 BLAKE      2850 JAMES,MARTIN,WARD,TURNER,ALLEN,BLAKE14 rows selected.