Sql Oracle中的listagg替代方案
假设我有以下基本数据:Sql Oracle中的listagg替代方案,sql,oracle,Sql,Oracle,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 J
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
我可以使用listagg()实现所需的输出:
但是它非常慢。对于我的真实数据集,它使查询运行时间变长35秒,而不是<1秒
我可以使用collect()
来加快速度吗?如果是,怎么做
我也听说过用户定义的聚合函数,但这些函数值得吗?我使用的是Tom Kyte of建议的以下用户定义函数-性能对我来说是可以接受的(尽管它在Oracle 8中不起作用)。你能试试这个吗
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
申请书
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.
很难相信用户定义的聚合函数会比Oracle的内置函数更快。你有这方面的基准吗?
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.