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PL / SQL提取列名並在select語句中使用

[英]PL/SQL Extract Column Names and use in select statement

亞行表

亞行表

今天的日期

今天的日期

我有一個亞行表。 我想基於系統日期提取列名稱

我目前正在嘗試以下不起作用的方法。

SELECT (
        SELECT DISTINCT TO_CHAR(TODAY, 'MON') || '_' || TO_CHAR(TODAY, 'D') AS TODAY
        FROM STTM_DATES
        )
FROM adb

我正在嘗試此腳本,但沒有結果集。

SQLSTMT VARCHAR2(2000); 
SQLSTMT := 'SELECT' || ' ' || (SELECT DISTINCT TO_CHAR(TODAY,'MON') || '_' || TO_CHAR(TODAY,'D')AS TODAY FROM STTM_DATES)||' ' || 'FROM ADB'; 
EXECUTE IMMEDIATE SQLSTMT; 

如果僅獲得一行,則需要一個目標來存儲該結果(和一個INTO表達式),例如

SQL> create table t ( a1 int, a2 int, a3 int );

Table created.

SQL>
SQL> insert into t values (1,2,3);

1 row created.

SQL>
SQL> set serverout on
SQL> declare
  2    col_name varchar2(30);
  3    result int;
  4  begin
  5    col_name := 'a1';
  6    execute immediate 'select '||col_name||' from t' into result;
  7    dbms_output.put_line(result);
  8
  9    col_name := 'a2';
 10    execute immediate 'select '||col_name||' from t' into result;
 11    dbms_output.put_line(result);
 12  end;
 13  /
1
2

PL/SQL procedure successfully completed.

如果接收到一組行,則需要在游標之間循環。

SQL>
SQL> insert into t values (4,5,6);

1 row created.

SQL>
SQL>
SQL> set serverout on
SQL> declare
  2    col_name varchar2(30) := 'a3';
  3    result int;
  4    rc sys_refcursor;
  5  begin
  6    open rc for 'select '||col_name||' from t';
  7    loop
  8      fetch rc into result;
  9      exit when rc%notfound;
 10      dbms_output.put_line(result);
 11    end loop;
 12    close rc;
 13  end;
 14  /
3
6

PL/SQL procedure successfully completed.

SQL>
SQL>

但是,這些都不能解決其他人對此處潛在設計問題表達的擔憂。

CREATE TABLE CUSTDET(CUSTACNO NUMBER, DT DATE, VAL NUMBER);
INSERT INTO CUSTDET VALUES(1, SYSDATE-2, 10);
INSERT INTO CUSTDET VALUES(1, SYSDATE-1, 20);
INSERT INTO CUSTDET VALUES(1, SYSDATE, 30);
INSERT INTO CUSTDET VALUES(2, SYSDATE-2, 40);
INSERT INTO CUSTDET VALUES(3, SYSDATE-1, 10);
INSERT INTO CUSTDET VALUES(3, SYSDATE, 20);
COMMIT;

您不需要為此使用動態SQL。

SELECT TO_CHAR(dt,'MON')||'_'||TO_CHAR(dt,'D') AS today FROM custdet;

輸出:

TODAY
MAR_1
MAR_2
MAR_3
MAR_1
MAR_2
MAR_3

如果要使用動態sql,則需要在變量或表變量中接收輸出以單獨顯示它。

DECLARE
    SQLSTMT VARCHAR2(2000); 
    TYPE MYTABTYP IS TABLE OF VARCHAR2(10);
    MYTABVAR MYTABTYP := MYTABTYP();
BEGIN
    SQLSTMT := q'[SELECT TO_CHAR(dt,'MON')||'_'||TO_CHAR(dt,'D') AS today FROM custdet]';
    EXECUTE IMMEDIATE SQLSTMT BULK COLLECT INTO MYTABVAR;
    FOR idx IN MYTABVAR.FIRST..MYTABVAR.LAST
    LOOP
        DBMS_OUTPUT.PUT_LINE(MYTABVAR(idx));
    END LOOP;
END;

輸出:

MAR_1
MAR_2
MAR_3
MAR_1
MAR_2
MAR_3

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