PL / SQL提取列名并在select语句中使用

Question

亚行表

今天的日期

我有一个亚行表。 我想基于系统日期提取列名称

我目前正在尝试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

我正在尝试此脚本，但没有结果集。

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; 

Answer 1

如果仅获得一行，则需要一个目标来存储该结果（和一个INTO表达式），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.

如果接收到一组行，则需要在游标之间循环。

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，这些都不能解决其他人对此处潜在设计问题表达的担忧。

Answer 2

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;

您不需要为此使用动态SQL。

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

输出：

TODAY
MAR_1
MAR_2
MAR_3
MAR_1
MAR_2
MAR_3

如果要使用动态sql，则需要在变量或表变量中接收输出以单独显示它。

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;

输出：

MAR_1
MAR_2
MAR_3
MAR_1
MAR_2
MAR_3