Data storage--sqlite Database storage--sql Statement--DML data Manipulation language, built-in function aggregation function

I. Connecting queries within a connection

Select a. field, B. field from table 1 A, table 2 B where a. field =b. Fields and ...

Two. DML Data Manipulation language

1. Add insert INTO values

1-insert into table name values (a list of values corresponding to all field one by one)

2-insert into table name (field list) values (a list that corresponds to the field list one by one)

3-insert into table name select corresponding field list from source table name where condition

4-insert into table name (field list) Select corresponding field list from source table name where condition

2. Delete delete

1-Full table Delete: Delete from table name

2-Select Delete: Delete from table name where condition

3. Change the update set

1-Full Table modification: Update table name set field name = new Value,...

2-Select Modify: Update table name set field name = new value,... WHERE condition

Three. Aggregation functions of built-in functions

1.COUNT Statistics Record Bar number

2.SUM () Total statistics

3.AVG statistical average

4.MAX returns the maximum value

5.MIN returns the minimum value

6. Features

1-can be used alone in a query or in conjunction with a group

2-If the field contents are null, the statistics are ignored

Data storage--sqlite Database storage--sql Statement--DML data Manipulation language, built-in function aggregation function