Data storage--sqlite Database storage--sql Statement--DQL data Query Language

I. WHERE query criteria

1. Operators

(1) is null/is NOT NULL to determine control/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 ' _ Condition '

6) Like ' condition _ '

(3) In judging if it is within the list of merits

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

①between start value and end value

② are included before and after

③ equivalent to field >= start value and field <= end value

④ used in numerical, time

⑤ Start value <= End value

(5) operator

2. Features

(1) Add filter condition to result set, return record of compound condition

(2) followed by the From table name

Two. Order by sort

1. Usage

①order by field 1 asc/desc, Field 2 ...

②order by Field ordinal (starting from 1)

③order by Field Alias

④order by field op-expression

2.ASC Ascending:

Default value

3.desc Descending

4. Sorting principle:

Top priority, if the previous data is consistent, sort by the following fields

Three. GROUP BY group

Usage: ①group by field List ②having filter records on a group basis

Data storage--sqlite Database storage--sql Statement--DQL data Query Language