Oracle SQL 中的 IF (CASE) THEN SELECT 语句

Question

我想在 Oracle 中创建一个如下所示的查询

DECLARE
   my_count NUMBER;
BEGIN
  SELECT COUNT(table.column1) INTO my_count FROM table;

  IF my_count > 2 THEN
     SELECT * FROM table WHERE table.column2 = 'ABC';
  ELSE
     SELECT * FROM table WHERE table.column2 != 'ABC';
  END IF;
END;

有同样效果的答案吗？

Answer 1

有这样的事吗？

with temp (cnt) as
  (select count(column1) from table)
select * from table cross join temp where column2 = 'ABC' and cnt > 2
union all
select * from table cross join temp where column2 <> 'ABC' and cnt <= 2;

---

演示，基于 Scott 的示例模式：有 4 名职员，并且 - 由于该数字大于 2，我将获取在部门 10 工作的员工（即将执行第 3 行中的查询）：

SQL> select count(*) from emp where job = 'CLERK';

  COUNT(*)
----------
         4

SQL> select ename from emp where deptno = 10;

ENAME
----------
CLARK
KING
MILLER
    
SQL> with temp (cnt) as
  2    (select count(*) from emp where job = 'CLERK')
  3  select ename from emp cross join temp where deptno = 10 and cnt > 2
  4  union all
  5  select ename from emp cross join temp where deptno <>10 and cnt <= 2;

ENAME
----------
CLARK             --> right; here they are
KING
MILLER

由于只有一位总统，计数低于 2，查询将返回第 5 行的结果：

SQL> with temp (cnt) as
  2    (select count(*) from emp where job = 'PRESIDENT')
  3  select ename from emp cross join temp where deptno = 10 and cnt > 2
  4  union all
  5  select ename from emp cross join temp where deptno <>10 and cnt <= 2;

ENAME
----------
BLAKE
SCOTT
TURNER
ADAMS
JAMES
FORD
SMITH
ALLEN
WARD
JONES
MARTIN

11 rows selected.

SQL>