在 where 条件中添加 case 语句并在 then 子句中提供条件语句

Question

我有一个 where 子句，我需要在其中添加 case 语句，在 then 和 else 中我必须给出条件语句。

我的 where 条件是这样的

WHERE 
    CASE
        WHEN 
        Substring(datename(dw,getdate()),1,3) = 'mon' 
        THEN convert(varchar,dt_start,103) = convert(varchar,dateadd(day,-3,getdate()),103) 
        AND  convert(varchar,dt_start,103) <= convert(varchar,dateadd(day,-2,getdate()),103)
        ELSE convert(varchar,dt_start,103) = convert(varchar,dateadd(day,-1,getdate()),103)
    END

但是此查询在 then 内的 = 处显示语法错误。同样的逻辑在 PostgreSQL 中起作用，但是当我在 SQL 服务器中尝试时，它在 = 处出现语法错误。我该如何解决这个问题。请帮忙
这是对应的 PGSQL 查询。

WHERE 
    CASE
        WHEN to_char(now(), 'dy'::text) = 'mon'::text THEN to_char(dt_start, 'yyyymmdd'::text) = to_char(now() - '3 days'::interval, 'yyyymmdd'::text) AND to_char(dt_start, 'yyyymmdd'::text) <= to_char(now() - '2 days'::interval, 'yyyymmdd'::text)
        ELSE to_char(dt_start, 'yyyymmdd'::text) = to_char(now() - '1 day'::interval, 'yyyymmdd'::text)
    END

Answer 1

试试这个

WHERE 
convert(varchar,dt_start,103)=
CASE
    WHEN 
    Substring(datename(dw,getdate()),1,3) = 'mon' 
    THEN convert(varchar,dt_start,103) = 
    convert(varchar,dateadd(day,-3,getdate()),103) 
    ELSE convert(varchar,dt_start,103) = 
    convert(varchar,dateadd(day,-1,getdate()),103)
END  

AND

convert(varchar,dt_start,103)<=
CASE
 WHEN 
 Substring(datename(dw,getdate()),1,3) = 'mon' 
  then convert(varchar,dateadd(day,-2,getdate()),103)
  else
  --put a condition that does not filter any data (maybe)
  convert(varchar,getdate(),103)
  end

Answer 2

试试这个：你必须根据你的要求制定两个单独的条件并记住一件事，你只能开始 CASE 作为 WHERE a = CASE 而不是WHERE CASE ...THEN a = b+c ... 或者在这种情况下，我建议使用动态查询，这样可以很容易地根据不同条件操作查询[=14=]

WHERE convert(varchar,dt_start,103) =
    CASE WHEN Substring(datename(dw,getdate()),1,3) = 'mon' THEN 
        convert(varchar,dateadd(day,-3,getdate()),103) 
    ELSE 
        convert(varchar,dateadd(day,-1,getdate()),103) 
    END

    AND convert(varchar,dt_start,103) <= 
    CASE WHEN Substring(datename(dw,getdate()),1,3) = 'mon' THEN
        convert(varchar,dateadd(day,-2,getdate()),103)
    ELSE 
        convert(varchar,dt_start,103)
    END

在 where 条件中添加 case 语句并在 then 子句中提供条件语句

Adding case statement inside where condition and provide conditional statements inside then clause

sql

sql-server

case

where-clause