oracle的concat字符串太长,自定义聚集函数,仿wm_concat,使用CLOB,可处理超过4000长度字符串...
时间: 2024-01-08 12:04:03 浏览: 35
是的,Oracle的`concat`函数只能处理4000个字符以下的字符串连接。如果需要处理更长的字符串,可以使用自定义聚合函数来实现。以下是一个示例函数,模仿Oracle的`wm_concat`函数:
```sql
CREATE OR REPLACE TYPE t_varchar2_list AS TABLE OF VARCHAR2(4000);
CREATE OR REPLACE FUNCTION wm_concat_clob (p_list t_varchar2_list)
RETURN CLOB
AGGREGATE USING wm_concat_clob_agg;
CREATE OR REPLACE TYPE wm_concat_clob_agg AS OBJECT
(
g_list CLOB,
STATIC FUNCTION ODCIAggregateInitialize (sctx IN OUT wm_concat_clob_agg)
RETURN NUMBER,
MEMBER FUNCTION ODCIAggregateIterate (
SELF IN OUT wm_concat_clob_agg,
VALUE IN VARCHAR2
) RETURN NUMBER,
MEMBER FUNCTION ODCIAggregateTerminate (
SELF IN wm_concat_clob_agg,
RETURN_VALUE OUT CLOB,
flags IN NUMBER
) RETURN NUMBER,
MEMBER FUNCTION ODCIAggregateMerge (
SELF IN OUT wm_concat_clob_agg,
ctx2 IN wm_concat_clob_agg
) RETURN NUMBER
);
CREATE OR REPLACE TYPE BODY wm_concat_clob_agg IS
STATIC FUNCTION ODCIAggregateInitialize (sctx IN OUT wm_concat_clob_agg)
RETURN NUMBER IS
BEGIN
sctx := wm_concat_clob_agg (NULL);
RETURN ODCIConst.SUCCESS;
END;
MEMBER FUNCTION ODCIAggregateIterate (
SELF IN OUT wm_concat_clob_agg,
VALUE IN VARCHAR2
) RETURN NUMBER IS
BEGIN
SELF.g_list := SELF.g_list || VALUE || ',';
RETURN ODCIConst.SUCCESS;
END;
MEMBER FUNCTION ODCIAggregateTerminate (
SELF IN wm_concat_clob_agg,
RETURN_VALUE OUT CLOB,
flags IN NUMBER
) RETURN NUMBER IS
BEGIN
RETURN_VALUE := rtrim (SELF.g_list, ',');
RETURN ODCIConst.SUCCESS;
END;
MEMBER FUNCTION ODCIAggregateMerge (
SELF IN OUT wm_concat_clob_agg,
ctx2 IN wm_concat_clob_agg
) RETURN NUMBER IS
BEGIN
SELF.g_list := SELF.g_list || ctx2.g_list;
RETURN ODCIConst.SUCCESS;
END;
END;
```
使用示例:
```sql
SELECT wm_concat_clob (CAST (COLLECT (column_name) AS t_varchar2_list))
FROM user_tab_columns
WHERE table_name = 'EMPLOYEES';
```
这将返回一个包含所有列名的CLOB字符串,无论它们的长度是多少。注意,由于使用CLOB,这可能会影响性能,因此请谨慎使用。