1. What is a data manipulation language
Data manipulation language DML (Data Manipulation Language) , through which users can realize basic operations on data.
2. Three forms of data manipulation language:
1) Insert: insert
2) Modify: update
3) Delete: delete
2.1 Insert statement
2.1.1 Method One of Inserting Statements: Classic Insertion
Syntax format:
insert into table name (column name 1,...) values (value 1,...);
2.1.1.1 Features of classic insert statements:
① The type of the inserted value must be consistent or compatible with the type of the column
②The column that cannot be null must insert a value, and it can be null
③The order of the columns can be exchanged, but the values must be exchanged with the order of the columns
④The number of columns and the number of values must be consistent
2.1.1.3 Case : Add an employee's information to the employee table (id 111, name Zhang San, gender male, phone 19888888)
insert into employees(employee_id,employee_name,employee_sex,employee_phone) values('111','张三','男','19888888');
2.1.2 The second way of inserting a statement:
Syntax format:
insert into table name set column name 1 = value 1, column name 2 = value 2...;
2.1.2.1 Case: Add an employee's information to the employee table (id 111, name Zhang San, gender male, phone 19888888)
insert into employees set employee_id=111,employee_name='张三',employee_sex='男',employee_phone='19888888';
2.1.3 The difference between the two methods
① Method one supports inserting multiple rows, and method two does not support
② Method one supports sub-queries, and method two does not support sub-queries
2.2 Modify the statement
2.2.1 Modify the syntax format of the statement
sql92 syntax:
update table 1 alias, table 2 alias set column = value where connection condition and filter condition;sql99 syntax:
update table 1 alias inner|left|right join table 2 alias on connection condition set column=value where filter condition;
2.2.2 Classification of modify statements: modify single-table records and modify multi-table records
2.2.2.1 Deletion of a single table
Method 1: delete can delete the entire row or the entire table
Syntax format: delete from table name [where filter condition limit number of entries]
Method 2: truncate delete the entire table (empty data)
Syntax format: truncate table table name;
2.2.2.2 Deletion of multiple tables
sql92:
delete the alias of table 1, the alias of table 2
from table 1 alias, table 2 alias
where join condition
and filter
sql99:
delete the alias of table 1, the alias of table 2
from Table 1 alias
inner|left|right join Table 2 alias on join conditions
where filter conditions
2.2.3 The difference between the two single table deletions
① delete can add where condition, truncate can not add
② Truncate deletes more efficiently
③ Add the table to be deleted by the self-growth long column. If you use delete to delete and then insert the data, the value of the self-growth column starts from the breakpoint; after truncate is deleted, the value of the self-growth column in the inserted data starts from 1.
④ truncate deletes without return value, delete deletes with return value (number of rows affected)
⑤ truncate delete can not be rolled back, delete delete can be rolled back.
Recommended
Recommended browser: Google Chrome
Recommended Java environment: IDEA (IntelliJ IDEA)
Recommended study this week: the study and application of JDBC
Recommended learning video link: https://www.bilibili.com/video/BV1eJ411c7rf?from=search&seid=2172690829084319707
Recommended practice Java environment: https://leetcode-cn.com/