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