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Editorial Team
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Asked: 2026-06-13T04:28:35+00:00

I have got three tables that are supposed to be joined, the query looks

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I have got three tables that are supposed to be joined, the query looks like this:

select distinct a.job 
from a
join  b on  a.job=b.id 
join  c on  c.id =a.path  
where c.path like '//depot/a/b/c/d/MARSR_CL286896_297899/%';

This query will always timeout. However, if I change the path comparison to some condition else, the query just run perfectly, for example:

 select distinct a.job 
 from a
 join  b on  a.job=b.id 
 join  c on  c.id =a.path  
 where c.path like '//depot/a/b/c/d/%';

Considering the difference of the path parameter, will the numbers and underscores the culprit that slows the statement? I have created index for the ‘path’ field

result of ‘explain’ command

1   SIMPLE  b   index   PRIMARY       job      62           73580   Using index; Using temporary
1   SIMPLE  a   ref     path,job      job       8   b.id    153 
1   SIMPLE  c   eq_ref  PRIMARY,path  PRIMARY   8   a.path  1   Using where
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1 Answer

  1. Editorial Team

    Yes. An underscore is a wildcard character too, which matches any (single) character, so this makes the query quite a lot more complex, since it can only use the index on the first part, until the first underscore, and needs to scan all matches on that part with a relatively complex regular expression to match the rest, while otherwise it could do a simple ‘starts with’.

    You should escape it to treat it as a normal underscore. You can escape it by adding a \ in front of the underscores. You can also escape a percent sign like this, using \% if you would need to.

    select distinct a.job 
from a
join  b on  a.job=b.id 
join  c on  c.id =a.path  
where c.path like '//depot/a/b/c/d/MARSR\_CL286896\_297899/%';
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