Tag: Subquery


From Months to Seconds with Subquery Materialization

In an earlier blog post, I showed how optimizer improvements in MySQL 5.6 gave better performance for several of the queries in the DBT-3 benchmark. However, for one of the queries, Query 18, I was not able to give exact numbers for the improvement since the query took very long in MySQL 5.5. I decided …


When is a Subquery Executed?

In an earlier blog post, I managed to confuse myself as to when a subquery was executed. It is not very clear from the output of EXPLAIN where the execution of a subquery takes place. Let’s take a look at the following example query (Query 17 in the DBT-3 benchmark):   select sum(l_extendedprice) / 7.0 …