Query tips for [MySQL] sub-statements

First, count the number of rows in the group BY statement

In a GROUP BY statement, if a field statistic function is included (such as: count (), SUM () ... In this case, the statistical function will only work on the group by field, so want to get the final result of the number of rows, can only rely on the return of the results through the program to traverse the count of rows, here is a problem, if the results of the query is too large, which will cost a lot of system resources, using subqueries can solve the problem

SELECT Count  as Count  from (SELECTsumas fromWHERE>1GROUP  by  having > 8900  as a

There are a few points to note:

1. You must specify a statistic field for the function (here is the Count function, specified a.id), cannot be a.*;

2. The child table must be aliased;

[MySQL] Sub-statement query tips