1
vote
0answers
39 views

Efficient query involving union and virtual/derived table [migrated]

Both of these mysql queries produce exactly the same result but query A is a simple union and it has the where postType clause embedded inside individual queries whereas query B has the same where ...
0
votes
1answer
440 views

Mysql: order by field or select union?

As a newbie, I expected Mysql to return the rows of this query ordered by their ids order in the id clause select * from test where id in (3,1,2) Unfortunatelly for me, that's not true. The results ...
1
vote
1answer
930 views

MySql: #1221 - Incorrect usage of UNION and ORDER BY

I have the following query which is intended to retrieve the newest 3 comments for each post in an array of posts. SELECT * FROM comment AS tbl WHERE sscm_id IN ( SELECT sscm_id FROM comment AS t1 ...
3
votes
1answer
5k views

MySQL: Optimize UNION with “ORDER BY” in inner queries

I just set up a logging system which consists of multiple tables with the same layout. There is one table for each data source. For the log viewer, I want to UNION all the log tables, filter them ...