[英]listagg alternative in Oracle
Let's say I have this base data: 假设我有以下基本数据:
DEPTNO ENAME
---------- ----------
20 SMITH
30 ALLEN
30 WARD
20 JONES
30 MARTIN
30 BLAKE
10 CLARK
20 SCOTT
10 KING
30 TURNER
20 ADAMS
30 JAMES
20 FORD
10 MILLER
I can achieve my desired output with listagg(): 我可以使用listagg()实现所需的输出:
SELECT deptno, LISTAGG(ename, ',') WITHIN GROUP (ORDER BY ename) AS employees
FROM emp
GROUP BY deptno;
DEPTNO EMPLOYEES
---------- --------------------------------------------------
10 CLARK,KING,MILLER
20 SMITH,FORD,ADAMS,SCOTT,JONES
30 ALLEN,BLAKE,MARTIN,TURNER,JAMES,WARD
But it is super slow. 但这非常慢。 With my real data set it makes the query run time 35 seconds long instead of < 1 second.
使用我的真实数据集,它使查询运行时间延长了35秒而不是<1秒。
Can I use collect()
to speed this up? 我可以使用
collect()
加快速度吗? If so, how? 如果是这样,怎么办?
I have also heard of user-defined aggregate functions, but are these worth it? 我也听说过用户定义的聚合函数,但是这些值得吗?
I use the following user-defined function as suggested by Tom Kyte of asktom - performance is acceptable to me (although it will not work in Oracle 8). 我使用了Asktom的Tom Kyte建议的以下用户定义函数-性能对我来说是可以接受的(尽管在Oracle 8中不起作用)。 Can you try this ?
你可以试试这个吗?
CREATE OR REPLACE TYPE t_string_agg AS OBJECT
(
g_string VARCHAR2(32767),
STATIC FUNCTION ODCIAggregateInitialize(sctx IN OUT t_string_agg)
RETURN NUMBER,
MEMBER FUNCTION ODCIAggregateIterate(self IN OUT t_string_agg,
value IN VARCHAR2 )
RETURN NUMBER,
MEMBER FUNCTION ODCIAggregateTerminate(self IN t_string_agg,
returnValue OUT VARCHAR2,
flags IN NUMBER)
RETURN NUMBER,
MEMBER FUNCTION ODCIAggregateMerge(self IN OUT t_string_agg,
ctx2 IN t_string_agg)
RETURN NUMBER
);
/
SHOW ERRORS
CREATE OR REPLACE TYPE BODY t_string_agg IS
STATIC FUNCTION ODCIAggregateInitialize(sctx IN OUT t_string_agg)
RETURN NUMBER IS
BEGIN
sctx := t_string_agg(NULL);
RETURN ODCIConst.Success;
END;
MEMBER FUNCTION ODCIAggregateIterate(self IN OUT t_string_agg,
value IN VARCHAR2 )
RETURN NUMBER IS
BEGIN
SELF.g_string := self.g_string || ',' || value;
RETURN ODCIConst.Success;
END;
MEMBER FUNCTION ODCIAggregateTerminate(self IN t_string_agg,
returnValue OUT VARCHAR2,
flags IN NUMBER)
RETURN NUMBER IS
BEGIN
returnValue := RTRIM(LTRIM(SELF.g_string, ','), ',');
RETURN ODCIConst.Success;
END;
MEMBER FUNCTION ODCIAggregateMerge(self IN OUT t_string_agg,
ctx2 IN t_string_agg)
RETURN NUMBER IS
BEGIN
SELF.g_string := SELF.g_string || ',' || ctx2.g_string;
RETURN ODCIConst.Success;
END;
END;
/
SHOW ERRORS
CREATE OR REPLACE FUNCTION string_agg (p_input VARCHAR2)
RETURN VARCHAR2
PARALLEL_ENABLE AGGREGATE USING t_string_agg;
/
SHOW ERRORS
Application, 应用,
COLUMN employees FORMAT A50
SELECT deptno, string_agg(ename) AS employees
FROM emp
GROUP BY deptno;
DEPTNO EMPLOYEES
---------- --------------------------------------------------
10 CLARK,KING,MILLER
20 SMITH,FORD,ADAMS,SCOTT,JONES
30 ALLEN,BLAKE,MARTIN,TURNER,JAMES,WARD
3 rows selected.
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