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0. preparation
Data files ：mysql Inquire about sql file - Dataset document class resources -CSDN library
1. insert data
1.1 The way 1：VALUES The way to add
         Using this syntax, you can only insert into a table at a time One data .
1.1.1 situation 1： Inserts data in the default order for all fields of the table
Grammar format :
        INSERT INTO Table name
        VALUES (value1,value2,....);
         In the value list, you need to specify a value for each field of the table , And the order of values must be the same as that of fields in the data table .
1.1.2 situation 2： Insert data for the specified fields of the table
Grammar format ：
        INSERT INTO Table name (column1 [, column2, …, columnn])
        VALUES (value1 [,value2, …, valuen]);
         Insert data for the specified fields of the table , Is in the INSERT Statement inserts values into only some fields , The values of other fields are the default values when the table is defined .
1.1.3 situation 3： Insert multiple records at the same time
        INSERT Statement can insert multiple records into the data table at the same time , Specify multiple value lists when inserting , Each value list is separated by commas .
Grammar format ：
        INSERT INTO table_name
        VALUES
        (value1 [,value2, …, valuen]),
        (value1 [,value2, …, valuen]),
        ……
        (value1 [,value2, …, valuen]);
or
        INSERT INTO table_name(column1 [, column2, …, columnn])
        VALUES
        (value1 [,value2, …, valuen]),
        (value1 [,value2, …, valuen]),
        ……
        (value1 [,value2, …, valuen]);
explain ：
1. Use INSERT When inserting multiple records at the same time ,MySQL It will return some additional information that is not available when performing single line insertion , The content of this information The meaning is as follows ： ●　Records： Indicates the number of records inserted . ●　Duplicates： Indicates the records that were ignored during insertion , The reason may be that Some records contain duplicate primary key values . ●　Warnings： Data values indicating a problem , For example, data type conversion occurs .
2. A that inserts multiple rows of records at the same time INSERT Statement is equivalent to multiple single line inserts INSERT sentence , But multi line INSERT sentence During processing More efficient . because MySQL Execute a single article INSERT Statement inserts more rows of data than using multiple INSERT sentence fast , Therefore, when inserting multiple records, it is best to choose to use a single record INSERT Insert... In the form of a statement .
1.1.4 Summary ：
1. VALUES Or you could write it as VALUE , however VALUES It's standard writing .
2. Character and date data should be enclosed in single quotes .
1.2 The way 2： Insert the query results into the table
        INSERT Can also be SELECT Insert the result of the statement query into the table , At this time, it is not necessary to input the values of each record one by one , just To use a INSERT Statement and a line SELECT Statements can be quickly inserted from one or more tables into a table Multiple lines .
Grammar format ：
        INSERT INTO Target table name
        (tar_column1 [, tar_column2, …, tar_columnn])
        SELECT
        (src_column1 [, src_column2, …, src_columnn])
        FROM Source table name
        [WHERE condition]
explain ：
1. stay INSERT Add a subquery to the statement .
2. There's no need to write VALUES Clause .
3. The list of values in the subquery should be the same as INSERT The column name in Clause corresponds to .
Be careful ：
        1. The data type of the query field must correspond to the data type of the field added to the table one by one
2. The length of the field added to the table cannot be less than the query field , Otherwise, there is a risk of unsuccessful addition .
2. Update data
Use UPDATE Statement update data . The grammar is as follows ：
        UPDATE table_name
        SET column1=value1, column2=value2, … , column=valuen
        [WHERE condition]
It can be updated at one time multiple data .
If you need to roll back data , It needs to be guaranteed in DML front , Set it up ：SET AUTOCOMMIT = FALSE;
notes ： Adding 、 When modifying or deleting data , There may be unsuccessful .（ When possible, due to the influence of constraints ）
3. Delete data
Use DELETE Statement to delete data from a table , The syntax is as follows ：
        DELETE FROM table_name
        [WHERE <condition>];
        table_name Specify the table to delete ;“[WHERE ]” Is an optional parameter , Specify deletion criteria , without WHERE Clause , DELETE Statement will delete all records in the table .
notes ： Adding 、 When modifying or deleting data , There may be unsuccessful .（ When possible, due to the influence of constraints ）

4. Summary
1.DML The operation is by default , After execution, the data will be submitted automatically , If you want to finish the execution , Do not submit data automatically , You need to use SET autocommit = FALSE;
2. Adding 、 When modifying or deleting data , There may be unsuccessful .（ When possible, due to the influence of constraints ）
3. Basic grammar ：
add to ： The way 1：
INSERT INTO Table name
                        VALUES (value1,value2,....);
The way 2：
                        INSERT INTO Target table name (tar_column1 [, tar_column2, …, tar_columnn])
                        SELECT (src_column1 [, src_column2, …, src_columnn])
                        FROM Source table name
                        [WHERE condition]
to update （ modify ）：
                        UPDATE table_name
                        SET column1=value1, column2=value2, … , column=valuen
                        [WHERE condition]
         Delete ：
                        DELETE FROM table_name
                        [WHERE <condition>];

5.mysql8.0 New characteristics : Calculated column
         What is a calculated column ？ Simply put, the value of a column is calculated from other columns . for example ,a The column value is 1、b The column value is 2,c Column Manual insertion is not required , Definition a+b As the result of the c Value , that c Is the calculation column , It is calculated from other columns .
         stay MySQL 8.0 in ,CREATE TABLE and ALTER TABLE Both support adding calculation Columns . Let's say CREATE TABLE For example .
6. practice
1. Create database dbtest11
CREATE DATABASE IF NOT EXISTS dbtest11 CHARACTER SET 'utf8';
2. Run the following script to create the table my_employees
USE dbtest11;
CREATE TABLE my_employees(
id INT(10),
first_name VARCHAR(10),
last_name VARCHAR(10),
userid VARCHAR(10),
salary DOUBLE(10,2)
);
CREATE TABLE users(
id INT,
userid VARCHAR(10),
department_id INT
);
3. Display table my_employees Structure

4. towards my_employees Insert the following data into the table

5. towards users Insert data into the table
1 Rpatel 10
2 Bdancs 10
3 Bbiri 20
4 Cnewman 30
5 Aropebur 40

6. take 3 Of employee No last_name It is amended as follows “drelxer”

7. All wages will be less than 900 The salary of the employee is modified to 1000

8. take userid by Bbiri Of user Table and my_employees All records in the table are deleted

9. Delete my_employees、users Table all data

10. Check the corrections made

11. Clear the table my_employees