1.MYSQL basic single-table data lookup statement

1. Some functions , such as lower (lowercase), upper (uppercase), Initcap (capital letter). It is particularly understood that sum (a) is the sum of the computed A, and count (a) is the number of records that contain a, calculated as the total number of records.

2. Basic statement selete from where Groub by has order by

3. Execution order: from where the group by has a select order by which table is found first, then according to what is divided, and then displayed, and then in what order.

The Order of writing: It is the right to put the select first, because order by is displayed in what order, so always put the last side.

4.group by what points

5.having Two filter, which is the two-time selection after the where group

6.order by what order are they sorted,

7.where and having all are the screening functions that play a role, so what's the difference?

(1) Where is the filter before grouping, and having is grouped

(2) Having a grouping function, where there is no

(3) If the same can be achieved, it is recommended to use where, more efficient

1.MYSQL basic single-table data lookup statement