使用EXECUTE IMMEDIATE和多个相同的绑定参数

Question

当我创建以下过程时

create or replace procedure check_exec_imm(
tab IN VARCHAR2,
col IN VARCHAR2,
col_name IN VARCHAR2

)

IS

 cv  SYS_REFCURSOR;
 col_value  VARCHAR2(32767);
 lv_query VARCHAR2(32767); 

 BEGIN
   lv_query := 'SELECT ' ||col||
           ' FROM ' ||tab||
           ' WHERE (:1 = ''EUR'' OR :1 = ''USD'') and rownum <=1';


    EXECUTE IMMEDIATE lv_query INTO col_value USING  col_name ;


DBMS_OUTPUT.PUT_LINE('COLUMN VALUE : ' || col_value);

END;

执行该过程时,我收到以下错误

ORA-01008: not all variables bound
ORA-06512: at "GRM_IV.CHECK_EXEC_IMM", line 18
ORA-06512: at line 2

当我再次给出bind参数col_name时,该过程运行正常.

EXECUTE IMMEDIATE lv_query INTO col_value USING  col_name, col_name ;

为什么oracle在此过程中表现不同.既然,它是相同的绑定变量,一个绑定参数应该足够了.. !!？请解释一下我的逻辑错误.

Answer 1

Oracle中存在"特殊"行为:动态SQL语句中的重复占位符名称

在匿名块或CALL语句中,如果名称相同,则不需要重复绑定值.例如,这个匿名块正在工作:

DECLARE
  a NUMBER := 4;
  b NUMBER := 7;
  plsql_block VARCHAR2(100);
BEGIN
  plsql_block := 'BEGIN calc_stats(:x, :x, :y, :x); END;';
  EXECUTE IMMEDIATE plsql_block USING a, b;  -- calc_stats(a, a, b, a)
END;
/

但这在程序中EXECUTE IMMEDIATE plsql_block USING a, b;不起作用.