Oracle条件条件where子句 [英] Oracle Conditional where clause

问题描述

有什么方法可以编写具有以下功能的查询，添加where子句作为条件方式，

is there any way to write query with following functionality, add where clause as a conditional way,

      select e.emp_id, emp.admin_user from employees e

如果emp.admin！='Y'

if emp.admin != 'Y'

然后

查询使用where子句

query run with where clause

其他

查询运行时没有where子句?

query run without where clause ?

推荐答案

在 WHERE 子句中使用 CASE 表达式应该可以解决问题.如果您说如果不满足条件就不需要where子句，那么您所需要的只是像WHERE 1 = 1这样的条件，即，当不满足条件时返回所有行.因此，您需要像往常一样将不满足条件设为 TRUE .

Using a CASE expression in the WHERE clause should do the trick. When you say you don't need the where clause if condition is not met, then all you want is a condition like WHERE 1 = 1, i.e. when condition is not met then return all rows. So, you need to make the not met condition as always TRUE.

例如，

我有一个员工表，

SQL> SELECT empno, ename, deptno
  2  FROM emp;

     EMPNO ENAME          DEPTNO
---------- ---------- ----------
      7369 SMITH              20
      7499 ALLEN              30
      7521 WARD               30
      7566 JONES              20
      7654 MARTIN             30
      7698 BLAKE              30
      7782 CLARK              10
      7788 SCOTT              20
      7839 KING               10
      7844 TURNER             30
      7876 ADAMS              20
      7900 JAMES              30
      7902 FORD               20
      7934 MILLER             10

14 rows selected.

SQL>

我想选择员工详细信息，如果部门为20，则使用where子句，否则返回所有员工详细信息，但过滤满足where条件的部门.

I want to select the employee details, if department is 20 then use the where clause else return all the employee details, but filter the department which meets the where condition.

SQL> SELECT empno, ename, deptno
  2  FROM emp
  3  WHERE ename =
  4    CASE
  5      WHEN deptno = 20
  6      THEN 'SCOTT'
  7      ELSE ename
  8    END
  9  /

     EMPNO ENAME          DEPTNO
---------- ---------- ----------
      7499 ALLEN              30
      7521 WARD               30
      7654 MARTIN             30
      7698 BLAKE              30
      7782 CLARK              10
      7788 SCOTT              20
      7839 KING               10
      7844 TURNER             30
      7900 JAMES              30
      7934 MILLER             10

10 rows selected.

SQL>

因此，对于部门20，该过滤器由where子句应用，而我仅获得ename SCOTT的行，对于其他人，它返回所有行.

So, for department 20, the filter is applied by where clause, and I get only the row for ename SCOTT, for others it returns all the rows.

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