DQL data Query Language of data storage--sqlite statement

A. SELECT statement

Format: Select field contents from table name

1. Field List

1-* all fields

2-comma interval list of field names

3-Specify aliases with AS (can be omitted)

2.DISTINCT de-duplication: DISTINCT Field List

Two. where query criteria

1.is null/is NOT NULL to determine NULL/non-NULL

2.like Fuzzy comparison string

1-wildcard characters

1>% any number of characters

2>_ single character

2-Usage

1>like '% condition '

2>like ' Condition% '

3>like '% condition% '

4>like ' _ Condition _ '

5>like ' Conditions _ '

6>like ' _ Condition '

3.in determine if the value is within the list

1-and equivalent to a single field or operation

2-Usage

1> field name in (value 1, value 2 ...) ）

2> field name in (subquery statement)

4.between and between the start and end values

1-between start value and end value

2-both front and rear included

3-equivalent To field >= start value and field <= end value

4-Used in numeric, time

5-Start value <= End value

4. Features

1-adding filters to the result set, returning records that match the criteria

2-follows the From table name

Three. Order by sort

1. Usage

1-order by field 1 ase/desc, Field 2 ...

2-order by Field ordinal (starting from 1)

3-order by Field Alias

4-order by field op-expression

2.ASC Ascending: Default value

3.desc Descending

4. Principle: Priority before, if the previous data is consistent, then sort by the following fields

Four. GROUP BY group

1. Usage

1-group by Field List

2-having filtering records on a group basis

DQL data Query Language of data storage--sqlite statement