usage:
Its role, the official interpretation of the document are as follows:
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.
I.e., within each group, LISTAGG column explants are ordered according to the order by clause, the results sorted spliced together.
measure_expr: it can be any expression-based column.
delimiter: delimiter, default NUL
order_by_clause: order by clause determines the order of column values are spliced.
By this use, it can be seen not only as a function of LISTAGG ordinary function, can also be used as analytical functions.
Usage order_by_clause and query_partition_clause as follows:
The following Examples illustrate the function:
Ordinary function, sort of wages, spliced with a comma.
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
Group function:
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
Analysis functions:
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.