技術標籤：EBS

對其作用，官方文件的解釋如下：

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.

即在每個分組內，LISTAGG根據order by子句對列植進行排序，將排序後的結果拼接起來。

measure_expr：可以是任何基於列的表示式。

delimiter：分隔符，預設為NUL

order_by_clause：order by子句決定了列值被拼接的順序。

通過該用法，可以看出LISTAGG函式不僅可作為一個普通函式使用，也可作為分析函式。

order_by_clause和query_partition_clause的用法如下：

下面對該函式進行舉例說明：

普通函式，對工資進行排序，用逗號進行拼接。

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

分組函式：

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

分析函式：

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,BLAKE

14 rows selected.