ORACLE过程中DISTINCT的替换函数

Question

我一直在尝试在**Procedure ORACLE中寻找**distinct **的替代方案。 ** 你能给我建议吗，因为**DISTINCT **不能在Procedure中使用。

我用过listagg等各种函数，但是没有任何效果

Answer 1

DISTINCT

不能在程序中使用。

是的，可以。

如果您有示例数据（包含重复行）：

CREATE TABLE table_name (a, b) AS
SELECT 1, 1 FROM DUAL CONNECT BY LEVEL <= 3 UNION ALL
SELECT 1, 2 FROM DUAL CONNECT BY LEVEL <= 4 UNION ALL
SELECT 2, 1 FROM DUAL CONNECT BY LEVEL <= 2 UNION ALL
SELECT 2, 2 FROM DUAL CONNECT BY LEVEL <= 5;

然后：

DECLARE
  PROCEDURE print_distinct_values
  IS
  BEGIN
    FOR r IN (SELECT DISTINCT * FROM table_name) LOOP
      DBMS_OUTPUT.PUT_LINE(r.a || ', ' || r.b);
    END LOOP;
  END;
BEGIN
  DBMS_OUTPUT.ENABLE();
  print_distinct_values();
END;
/

输出：

1, 1
1, 2
2, 1
2, 2

如果您想要相同的输出，那么您也可以使用查询（带或不带

PROCEDURE

）：

SELECT a, b FROM table_name GROUP BY a, b

或：

SELECT a, b
FROM   table_name
ORDER BY ROW_NUMBER() OVER (PARTITION BY a, b ORDER BY ROWNUM)
FETCH FIRST ROW WITH TIES

或：

SELECT a, b
FROM   (
  SELECT a, b,
         ROW_NUMBER() OVER (PARTITION BY a, b ORDER BY ROWNUM) AS rn
  FROM   table_name
)
WHERE  rn = 1

所有输出都相同。

小提琴

Answer 2

幸运的猜测：正如您提到的LISTAGG，您是否尝试过使用

LISTAGG(DISTINCT ...)

但它不起作用？如果是这样，则意味着您的数据库版本不支持该语法；你必须在19c。

对于较低版本，请使用内联视图来获取不同的值，然后将

LISTAGG

应用于其结果集。

---

演示：这是11g：

SQL> select listagg(distinct job, ', ') within group (order by job) as result from emp;
select listagg(distinct job, ', ') within group (order by job) from emp
       *
ERROR at line 1:
ORA-30482: DISTINCT option not allowed for this function

内联视图（第2行）；我相信这就是您正在寻找的：

SQL> select listagg(job, ', ') within group (order by job) as result
  2  from (select distinct job from emp);

RESULT
--------------------------------------------------------------------------------
ANALYST, CLERK, MANAGER, PRESIDENT, SALESMAN

SQL>

19c（支持

DISTINCT

内的

LISTAGG

）：

SQL> select listagg(distinct job, ', ') within group (order by job) as result from emp;
RESULT
--------------------------------------------------------------------------------
ANALYST, CLERK, MANAGER, PRESIDENT, SALESMAN

SQL>

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如果我猜错了，没问题；我会修复这个答案，或者删除它。