MySQL notes (ii)

One, DQL statements
1. Constant column
SELECT
' Studentname ' as the name,
' Address ' as,
' Beijing Information Center ' as school name
From ' student ';
2. Common functions
Aggregation functions
AVG () averaging points
COUNT () Statistics Record count
SELECT COUNT (1) from student; High efficiency
Select COUNT (*) from student;
Max () max value
Min () Min value
SUM () sum
String functions:
Date function:
Curdate ();
#获取随机数
Select Floor (RAND () *10);
3. Sort Query
ORDER BY [Desc]

4. * Paging Query
Limit
5, sub-query

Comparison operators (such as >, =, <, >=, <=, and so on) can return only one value

In and not in can return multiple single-segment values.
Execute the subquery first and then execute the parent query

MySQL notes (ii)