Union, der forårsager et ORA-01790:-udtryk, skal have samme datatype som det tilsvarende udtryk

Jeg tror, ​​du ikke kan lave en sådan casting i SQL. Men i PL/SQL kan du:

CREATE OR REPLACE TYPE STRARRAY AS TABLE OF VARCHAR2 (255)
/

DECLARE
  tab STRARRAY;
  cnt NUMBER:= 0;
BEGIN
 SELECT COUNT(*)
  INTO cnt
   FROM TABLE(CAST(tab AS strarray));
  dbms_output.put_line(cnt);
END;
/

Jeg tror, ​​jeg tog fejl i mine antagelser ovenfor. Jeg slettede det ikke, da det stadig er et gyldigt eksempel. Nedenfor eksempel casting af eksisterende tabelkolonne (emp table) med COLLECT som type table_type:

CREATE OR REPLACE TYPE varchar2_ntt AS TABLE OF VARCHAR2(4000);
/

SELECT deptno
    , CAST(COLLECT(ename) AS varchar2_ntt) AS emps
  FROM   scott.emp
GROUP  BY deptno
/

-- This is dumb but works:

SELECT deptno
     , CAST(COLLECT(ename) AS varchar2_ntt) AS emps
  FROM   scott.emp
 GROUP  BY deptno
 UNION ALL
 SELECT deptno
     , CAST(COLLECT(ename) AS varchar2_ntt) AS emps
   FROM   scott.emp
  GROUP  BY deptno
 /