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

当我再次给出绑定参数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.. !!？请解释我的逻辑错误.