使用第二个INNER JOIN或之前的两个表的带有INNER JOIN的SQL

Question

    select 
    sld.linkid,sld.accept,scd.catid,scd.catname,scd.caturl,scd1.parentcatid
    from sound_link_droos sld
    INNER JOIN sound_cat_droos scd
    ON sld.catid=scd.catid 
OR
    INNER JOIN  sound_cat_droos scd1 
    ON sld.catid=scd1.parentcatid
    WHERE accept = '1' AND scd.catname = '$catname'");

i want to know if i can have or in this statment or ... if the one inner join return fals

sound_cat_droos

Catidcatnameparentidaccepturl 1David01http://www.example.com 2Jazz music11http://www.example.com

sound_link_droos

linkidlinknamecatidaccepturl 1my love11http://www.example.com/audio.mp3 2my baby 21http://www.example.com/audio.mp3

Answer 1

Best solution is to use Union all Instead of OR in Join as given below:

select sld.linkid,sld.accept,scd.catid,scd.catname,scd.caturl,scd1.parentcatid from sound_link_droos sld
INNER JOIN sound_cat_droos scd
ON sld.catid=scd.catid 
where accept = '1' and scd.catname = '$catname'
union all
select sld.linkid,sld.accept,scd.catid,scd.catname,scd.caturl,scd1.parentcatid from sound_link_droos sld
INNER JOIN  sound_cat_droos scd1 
ON sld.catid=scd1.parentcatid
where accept = '1' and scd1.catname = '$catname';

Answer 2

You can express or logic in the on clause like this:

select sld.linkid, sld.accept,s cd.catid, scd.catname, scd.caturl, scd1.parentcatid
from sound_link_droos sld inner join
     sound_cat_droos scd
     on sld.catid = scd.catid or sld.catid = scd.parentcatid 
where accept = 1 and scd.catname = '$catname';

Such joins are usually performance killers, and this might not do what you really want. If not, ask another question with sample data and desired results.

I removed the single quotes around the '1' , because I'm guessing the value is numeric. Numbers should be compared to numbers.

It is also obligatory to mention parameters. You should not be munging a query string with parameter values. Learn how to properly use parameters.

Answer 3

Without a specification, we can only guess at what the query is supposed to return.

So here's a guess.

We get all _cat_ where catname matches some value:

  SELECT scd.catid
       , scd.catname
       , scd.caturl
    FROM sound_cat_droos scd 
   WHERE scd.catname = 'someval' 

We know that a _cat_ could be the parent of other _cat_ . And we want to also return those children _cat_ . Here's a query to do that:

  SELECT scc.catid
       , scc.catname
       , scc.caturl
    FROM sound_cat_droos scc
    JOIN sound_cat_droos scp
      ON scp.catid = scc.parentcatid
   WHERE scp.catname = 'someval'

We can use a UNION ALL set operator to combine the results from those two queries into a single set. And then we can join that combined set to _link_

  SELECT sld.linkid
       , sld.accept
       , sca.catid
       , sca.catname
       , sca.caturl
    FROM ( SELECT scd.catid
                , scd.catname
                , scd.caturl
             FROM sound_cat_droos scd 
            WHERE scd.catname = 'someval' 
            UNION ALL 
           SELECT scc.catid
                , scc.catname
                , scc.caturl
             FROM sound_cat_droos scc
             JOIN sound_cat_droos scp
               ON scp.catid = scc.parentcatid
            WHERE scp.catname = 'someval'
         ) sca
    JOIN sound_link_droos sld
      ON sld.catid = sca.catid
     AND sld.accept = '1'

If it's important (for some reason) to know whether the _cat_ we matched was a direct match, or was a match to a child _cat_ , we can include a discriminator column in the inline view query, and return that in the resultset.

  SELECT sld.linkid
       , sld.accept
       , sca.catid
       , sca.catname
       , sca.caturl
       , sca.src
    FROM ( SELECT 1 AS src
                , scd.catid
                , scd.catname
                , scd.caturl
             FROM sound_cat_droos scd 
            WHERE scd.catname = 'someval' 
            UNION ALL 
           SELECT 2 AS src
                , scc.catid
                , scc.catname
                , scc.caturl
             FROM sound_cat_droos scc
             JOIN sound_cat_droos scp
               ON scp.catid = scc.parentcatid
            WHERE scp.catname = 'someval'
         ) sca
    JOIN sound_link_droos sld
      ON sld.catid = sca.catid
     AND sld.accept = '1'

We're just guessing at the requirements, at what result should be returned. And this query might satisfy your specification. But we don't what that specification is.