Mysql if语句在where子句中

Question

I have a code that is not working

SELECT DISTINCT CONCAT(u.firstname, ' ', u.lastname) AS fnameLname, s.student_number, u.user_id
FROM user u
LEFT OUTER JOIN student s ON u.user_id = s.user_id
WHERE 
case when @filter != ''
then ((u.firstname REGEXP CONCAT('^[', @filter, ']') OR u.lastname REGEXP CONCAT('^[', @filter, ']')) OR student_number REGEXP CONCAT('^[', @filter, ']'))
else 1=1 
AND (u.user_type_id = 0)
ORDER BY u.lastname, u.firstname

I want to select users from table user , I have implement search field (for searching on student_number or on start of firstname and lastname (just first letter of firstname or lastname)).

For example, if I search for "js", it would match for example John Smith, and not John Moses. It would also match Jeremy Sassone. @filter is control parameter in asp.net.

Could anyone help me?

Answer 1

You could use and and or for this. No need for the complicated case when s, and inner case when s, etc.:

where ( ( @filter != '%'
          and ( u.firstname REGEXP CONCAT('^[', @filter, ']')
                or u.lastname REGEXP CONCAT('^[', @filter, ']')
                or student_number REGEXP CONCAT('^[', @filter, ']')
             )
       )
       or @filter = '%'
      )
and   u.user_type_id = 0

The default value for @filter would be '%' - with an empty string it's a syntax error because of the empty square brackets.