SQL basic statement DQL select and extract DML insert delete

SQL Sentences can be roughly divided into four categories ：

1） DDL： Data definition language , establish 、 Delete 、 modify the database 、 Data table .

2） DML： Data management language , Add the data in the data table 、 Delete 、 Modify the operating .

3） DQL： Data query language , Query the data in the data table .

4） DCL： Data control language , Permissions on the database 、 Role, etc .

Here first write DQL sentence

Simple query

The simplest select

select  Field list  from  Table name  

Field and table rename

select  Field name  as  Alias ,  Field name  as  Alias  from  Table name  as  Alias 

where

Filter query records . Only records that meet the screening criteria , Will appear in the query results .

1） Comparison operator

Operator effect

“>” Greater than
“>=” Greater than or equal to
"<" Less than
“<=” Less than or equal to
“=” be equal to
“!=,<>” It's not equal to
null Value does not participate in the comparison operation

2） Logical operators

Operator effect

and Logic and
or Logic or
not Logic is not

3） Null Value judgment

Operator effect

is null Field is null
is not null Field is not null

4） between…and…

Range of judgment , Closed interval .
amount to Field >= value and Field <= value .

5） Fuzzy query

 Field  like ' The rules '
 The rules ： % Represents any number of arbitrary characters ,_ Represents any character .

SQL Case insensitive ,like,= They're all case insensitive .

6） in

 Field  in ( value ,  value ,  value ...)
 Field  not in ( value ,  value ,  value ...)

Group query

Use group by In the queried data , Grouping , Records with the same specified fields will be merged into a group .

group by  Field name , ...
group by 1, 2, ...  //  The subscript of the field , from 1 Start