logic executed sequentially select statement:

logic executed sequentially select statement:
1.From: all records in the lookup table, to generate the result set
2.join: according to the connection condition, generate a result set
3.where: Step 2 to produce the result set with the back where
the conditional expression screening each record
4.group by: only the groups after the grouping operation, the column select clause packet can only occur
or aggregate functions
5.having: screening of group
6.select: output results
7.order by: to sort the query output