mysql查询的where子句中的if条件动态生成

Question

Hi i am trying to write a query with if in where clause please suggest how can i do it my where condition is as follow

 IF(`page_type` ==1,
    `pages NOT LIKE '%ads/indian-institute-of-technology-bombay.html%' 
  OR pages NOT LIKE '%ads/*%' OR pages NOT LIKE '%indian-institute-of-technology-bombay.html/*%'` ,
   ` pages LIKE '%ads/indian-institute-of-technology-bombay.html%'
  OR pages LIKE '%ads/*%' OR
     pages LIKE '%indian-institute-of-technology-bombay.html/*%'` )

Full Query is

SELECT  *
    FROM  `app_slides`
    WHERE  IF(`page_type` ==1, `pages NOT LIKE '%ads/indian-institute-of-technology-bombay.html%'
              OR  pages NOT LIKE '%ads/*%'
              OR  pages NOT LIKE '%indian-institute-of-technology-bombay.html/*%'` ,
                ` pages LIKE '%ads/indian-institute-of-technology-bombay.html%'
              OR  pages LIKE '%ads/*%'
              OR  pages LIKE '%indian-institute-of-technology-bombay.html/*%'` 
             )

Answer 1

IF works like this:

IF(<condition>, <value if true>, <value if false>)

So as an example

SELECT IF( 'a' = 'a', 1, 0 ); //will return 1
SELECT IF( 'a' = 'b', 1, 0 );//will return 0

Using IF in a WHERE query The following example shows how to use IF in a WHERE query.

SELECT ...
WHERE ...
AND IF(myfield = 'somevalue', 1, 0) = 1

Answer 2

This should not be done in an if, but should be expressed using the logical operators.

select ... from ... where (`page_type` == 1 and ... )
or (`page_type` <>1 and ...)

you may optimize it by rewriting as a union instead of using or in the where criteria.

Answer 3

You can use case for this. Case statement work like this.

SELECT empno, ename, job
  FROM scott.emp
 WHERE (CASE WHEN job = 'MANAGER' THEN '1'  
         WHEN job = 'CLERK'   THEN '2' 
         ELSE '0'  END) IN (1, 2)

Answer 4

You have one or two bugs that the other answers do not address...

   x NOT LIKE 'a'
OR x NOT LIKE 'b'

is always TRUE. Hence, the first part of the IF will always succeed. Perhaps you want

NOT (   x LIKE 'a'
     OR x LIKE 'b' )

specifically,

NOT (   `pages LIKE '%ads/indian-institute-of-technology-bombay.html%' 
      OR pages LIKE '%ads/*%'
      OR pages LIKE '%indian-institute-of-technology-bombay.html/*%'` )

The other possible bug:

ads/*

Is that actually what you are expecting? Note that * , when used in LIKE is not the same as when used in RLIKE .

It does not really matter whether you use IF , CASE , or page_type == 1 and (...) -- each will perform approximately equally. And each will come up with the desired results (after fixing the bug(s) I pointed out). And each will be slow -- that is, each will do a full table scan. This is for 2 reasons:

• Leading wild cards ( LIKE '%...' ) does not optimize well.
• OR does not optimize well. (And changing to UNION is useful only if you get rid of all the ORs and the leading wildcards).