SQL Server 2012中“ WHERE”子句中的“ CASE”语句

Question

i have a select statement like this

select x, y , z from table a
where CAST( CAST(DATEColumn AS VARCHAR) AS DATE) between  
    case when a.columnx = '1900-01-01' then CAST( CAST(DATEColumn AS VARCHAR) AS DATE) else c.columnx end
    and cast( c.CustomerShipToRecTrmDt as date)

why does this case statement does not work whereas the case statement works if i hardcode the dates?

Answer 1

What are you casting a date columns to varchar and then back to a date ? I think this does what you want:

select x, y , z 
rom table a
where DATEColumn  between  
          (case when a.columnx = '1900-01-01' then DATEColumn else cast(c.columnx as date) end and
          cast( c.CustomerShipToRecTrmDt as date)

You can eliminate the case statement from the where clause by doing:

where DATEColumn >= cast(c.columnx as date) and DateColumns <= cast( c.CustomerShipToRecTrmDt as date)

The comparison to 1900-01-01 doesn't affect the >= part, unless you are working with dates before 1900 (I'm guessing this is unlikely).

Also, whenever casting values to varchar() , always include the length (as in varchar(255) ).