如何在where子句中使用case

I want to get only status = 1 records. But I don't have status column in my table. So I derived the value using CASE... WHEN... THEN. But when I try to use case in where clause, It shows syntax error.

我想只获得status = 1条记录。但我的表格中没有状态栏。所以我使用CASE ... WHEN ...那么得出了价值。但是当我尝试在where子句中使用case时,它显示语法错误。

my query

SELECT SQL_CALC_FOUND_ROWS *,
    CASE
        WHEN quantity > num_used AND (CURDATE() BETWEEN coupon_start_date AND coupon_end_date) THEN '1'
        ELSE '0'
    END AS STATUS
FROM
    table_coupon_code
WHERE
    (CASE
        WHEN quantity > num_used AND (CURDATE() BETWEEN coupon_start_date AND coupon_end_date) THEN '1'
        ELSE '0'
    END AS STATUS) = '1' AND coupon_status <> '2'

How can I do this ?

我怎样才能做到这一点 ?

4 个解决方案

#1

remove AS STATUS from where clause

从where子句中删除AS STATUS

SELECT SQL_CALC_FOUND_ROWS * ,
  CASE WHEN quantity > num_used AND (CURDATE( ) BETWEEN coupon_start_date AND coupon_end_date)
  THEN '1'
  ELSE '0'
  END AS STATUS
FROM table_coupon_code
WHERE 
CASE WHEN quantity > num_used AND (CURDATE( ) BETWEEN coupon_start_date AND coupon_end_date)
  THEN '1'
  ELSE '0'
  END = '1'
AND coupon_status <> '2'

But your CASE is really unnecessary. Just use your CASE condition as stand-alone WHEREcondition, like

但你的CASE真的没必要。只需将您的CASE条件用作独立的WHEREcondition,就像

[...]
WHERE quantity > num_used AND
CURDATE( ) BETWEEN coupon_start_date AND coupon_end_date AND
coupon_status <> '2'

#2

If you do not want to repeat the case statement you could wrap the select in a subselect or make a view. Subselect is something like

如果您不想重复case语句,可以将select包装在子选择中或创建视图。次选是类似的

select status 
  from (select case 
          when zip like '4321%' then 1 else 0 end as status
          from adr 
       ) t 
 where status = 1;

#3

Nobody Suggested the HAVING Clause?

没有人建议使用HAVING条款?

This allows you to query the selected columns, instead of the actual results. Great for using case and function calls.

这允许您查询选定的列,而不是实际结果。非常适合使用大小写和函数调用。

#4

I suppose you have some other, more complicated query, as the one you have provided is equivalent to:

我想你有一些其他更复杂的查询,因为你提供的查询相当于:

SELECT SQL_CALC_FOUND_ROWS * ,
       '1' AS STATUS
FROM table_coupon_code
WHERE quantity > num_used
  AND CURDATE() BETWEEN coupon_start_date AND coupon_end_date
  AND coupon_status <> '2'

#1