The explain tag has no wiki summary.
1
vote
1answer
59 views
Fast query, in theory using index, still in the slow-query log
I'm having a hard time interpreting the EXPLAIN results of these queries. They both end up in the slow-query log, but the execution time is ~0.0050ms and the final result set is always under 100 rows.
...
0
votes
1answer
28 views
Is there any manual for the visual explain in mysql? The output plan is unreadable
Just like this example, I cannot even tell the join ordering from it. And what does "ALL" and "ref" in the table mean? Is there any manual about the visual explain?
1
vote
1answer
61 views
Query optimization when no row is returned
I am using explain to figure out what is happening in my query which is:
explain select t from c where u1_id = 1 group by t;
I see "Using where" in the Extra column of the resultset. But this only ...
3
votes
3answers
182 views
Optimizing queries on a range of timestamps (two columns)
I use postgresql-9.1 with ubuntu 12.04.
I need to select records inside a range of time: my table time_limits has two timestamp fields and one property integer. Indeed there are other info columns ...
1
vote
0answers
59 views
Mysql: Large Query with subqueries optimization
Any query optimization gurus in the house??
Anyway, I am trying to attack this on two fronts, one being to code a way around it but secondly, I'm thinking some real optimization might help in the ...
1
vote
2answers
109 views
Mysql: Large Query with subqueries optimization
Any query optimization gurus in the house??
Anyway, I trying to attach this on two fronts, one I'm trying to code a way around it but secondly, I'm thinking some real optimization might help in the ...
5
votes
2answers
95 views
mysql join by 2 ways - how it works? - which gives performance difference
I had 2 different ways to query the content which showed performance difference when executed. The 1st way is
EXPLAIN select SOME_COLUMNS
from
( select *
from A
where CONDITION
) p
inner join
( ...
1
vote
1answer
372 views
Why I cannot let EXPLAIN update statements?
I can imagine that it's actually more important to explain SELECT statements, but I wonder why there's no possibility to use EXPLAIN on UPDATEs/INSERTs. I may use a WHERE-statement in an UPDATE where ...
3
votes
2answers
2k views
Why am I getting `Impossible WHERE noticed after reading const tables` in explain query?
I have a unique compound key like fr(fromid,toid) in the table, when I run the query with explain I get the following result:
Impossible WHERE noticed after reading const tables`
The query I ran:
...
