Single-table query of SQL statements

Syntax Order :

Select DISTINCT field 1, Field 2, Field 3 from library. Table

Where condition

GROUP BY group conditions

Having the filter # execution order, this step returns to running the SELECT statement before running the order by

Order by Sort Field

Limit n; # limits the number of bars to print to the screen

Where required before group BY, the aggregate function is not available

Hanving required after group BY, aggregate functions are available

An aggregate function, such as SELECT COUNT (ID), can be used after select from employee

Execution Order :

From->where->group By->having->distinct->order By->limit

# GROUP BY

Set mysql> set global sql_mode= "only_full_group_by"; #select只能取分组的字段

Select post from the employee group by post, but not select * FROM Employee GROUP by post;

# Group_concat

Link the value of a field in a record of group by, such as Select Post,group_concat (name) from the employee group by post;

# having

SELECT * from the employee GROUP by Post have the count (id) <2;

# ORDER BY

SELECT * from-Employee ORDER BY-age desc,id ASC;

# limit

SELECT * FROM Employee limit 0, 5;

SELECT * FROM Employee limit 5, 5; # pagination

Single-table query of SQL statements