oracle的concat字符串太长,怎么处理

是的，当字符串长度超过4000时，Oracle的concat函数无法处理。但是，您可以使用自定义聚合函数来解决这个问题。 下面是一个例子：创建一个自定义聚合函数，它将所有输入字符串连接起来，并返回一个CLOB类型的结果： CREATE OR REPLACE TYPE STR_CONCAT_TYPE AS OBJECT str CLOB, STATIC FUNCTION ODCIAggregateInitialize(sctx IN OUT STR_CONCAT_TYPE) RETURN NUMBER, MEMBER FUNCTION ODCIAggregateIterate(self IN OUT STR_CONCAT_TYPE, value IN VARCHAR2) RETURN NUMBER, MEMBER FUNCTION ODCIAggregateTerminate(self IN STR_CONCAT_TYPE, returnValue OUT CLOB, flags IN NUMBER) RETURN NUMBER, MEMBER FUNCTION ODCIAggregateMerge(self IN OUT STR_CONCAT_TYPE, ctx2 IN STR_CONCAT_TYPE) RETURN NUMBER CREATE OR REPLACE TYPE BODY STR_CONCAT_TYPE IS STATIC FUNCTION ODCIAggregateInitialize(sctx IN OUT STR_CONCAT_TYPE) RETURN NUMBER IS BEGIN sctx := STR_CONCAT_TYPE(''); RETURN ODCIConst.Success; MEMBER FUNCTION ODCIAggregateIterate(self IN OUT STR_CONCAT_TYPE, value IN VARCHAR2) RETURN NUMBER IS BEGIN self.str := self.str || value; RETURN ODCIConst.Success; MEMBER FUNCTION ODCIAggregateTerminate(self IN STR_CONCAT_TYPE, returnValue OUT CLOB, flags IN NUMBER) RETURN NUMBER IS BEGIN returnValue := self.str; RETURN ODCIConst.Success; MEMBER FUNCTION ODCIAggregateMerge(self IN OUT STR_CONCAT_TYPE, ctx2 IN STR_CONCAT_TYPE) RETURN NUMBER IS BEGIN self.str := self.str || ctx2.str; RETURN ODCIConst.Success; CREATE OR REPLACE FUNCTION str_concat(input VARCHAR2) RETURN CLOB AGGREGATE USING STR_CONCAT_TYPE; ```

在 Oracle 中，可以使用自定义聚合函数来实现类似于 `wm_concat` 的功能，该函数可以将多行字符串按照指定的分隔符拼接成一个 CLOB 类型的字符串，并返回该字符串。 以下是一个示例代码： ```sql CREATE OR REPLACE TYPE t_string_agg AS OBJECT g_string CLOB, 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 CLOB, flags IN NUMBER) RETURN NUMBER, MEMBER FUNCTION ODCIAggregateMerge(self IN OUT t_string_agg, ctx2 IN t_string_agg) RETURN NUMBER 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(CLOB('')); RETURN ODCIConst.Success; MEMBER FUNCTION ODCIAggregateIterate(self IN OUT t_string_agg, value IN VARCHAR2) RETURN NUMBER IS BEGIN IF self.g_string IS NULL THEN self.g_string := value; self.g_string := self.g_string || ', ' || value; END IF; RETURN ODCIConst.Success; MEMBER FUNCTION ODCIAggregateTerminate(self IN t_string_agg, returnValue OUT CLOB, flags IN NUMBER) RETURN NUMBER IS BEGIN returnValue := self.g_string; RETURN ODCIConst.Success; MEMBER FUNCTION ODCIAggregateMerge(self IN OUT t_string_agg, ctx2 IN t_string_agg) RETURN NUMBER IS BEGIN IF self.g_string IS NULL THEN self.g_string := ctx2.g_string; self.g_string := self.g_string || ', ' || ctx2.g_string; END IF; RETURN ODCIConst.Success; CREATE OR REPLACE FUNCTION string_agg(input VARCHAR2) RETURN CLOB AGGREGATE USING t_string_agg; ```