Basic SQL DQL

Catalog

grammar

The basic query

Conditions of the query

Aggregate functions

Group query

Sort query

  Paging query

Execution order

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grammar

select+ Field list	The basic query
from+ List of table names	The basic query
where+ List of conditions	Conditions of the query
group by+ Group field list	Group query
having+ Condition list after grouping	Group query
order by+ Sort field list	Sort query
limt+ Paging parameters	Paging query

The basic query

1. Query multiple fields

select  Field 1, Field 2, Field 3,…… from  Table name ;

select * from  Table name ;

2. Set alias

select  Field 1 [as  Alias 1], Field 2[as  Alias 2] …… from  Table name ;

3. Remove duplicate records

select distinct  Field list  from  Table name 

Conditions of the query

grammar

select  Field list  from  Table name  where  List of conditions ;

Conditions

 

Aggregate functions

Take a column of data as a whole , Do the longitudinal calculation .

grammar

select Aggregate functions ( Field list ) from Table name ; 

Group query

grammar

select  Field list  from  Table name  [where  Conditions ] group by  Group field name  [having  Filter conditions after grouping ];

Sort query

grammar

select  Field list  from  Table name  order by  Field 1  sort order 1, Field 2, sort order 2;

sort order

1. asc： Ascending ( Default )

2. desc： Descending

  Paging query

grammar

select  Field list  from  Table name  limit  Actually , Number of query records ;

Be careful

Starting index from 0 Start , Starting index =（ Look up the page number -1）* Each page shows the number of records .

Paging query is the dialect of database , Different databases have different implementations ,mysql Medium is limit.

If the query is the first page of data , The starting index can be omitted , Directly abbreviated as limit 10.

Execution order