MySQL Tutorial: Basic Operations of SQL Data

This article mainly introduces you to the basic operations of SQL data. I hope it will be helpful to friends in need!

Recommended reference tutorial: "SQL Tutorial"

SQL basic operations

Basic operations: CURD, that isadd, delete, modify, query .

According to different operation objects, we can divide the basic operations of SQL into three categories: library operations, table (field) operations and data operations.

Data operation

1 Add new data

There are two methods for adding new data.

• Type 1: Insert data into the entire table field. There is no need to specify a field list, but the order in which the data values ​​appear must match the fields in the table. The order is consistent, and all non-numeric data needs to be enclosed in quotation marks (single quotation marks are recommended).
  

• Basic syntax: insert into table name values(value list)[,(value list)];

• Example:insert into test values('charies',18,'3.1');

• 2nd Type: To insert data into some fields, you need to select the field list. The order in which the fields appear in the field list has nothing to do with the order of the fields in the table, but the order of the field values ​​in the value list must be consistent with the order in the field list.
  

• Basic syntax: insert into table name (field list) values ​​(value list) [, (value list)];

• Example: insert into test(age,name) values(18,'guo');

##2 Query data

View all–> Basic syntax:

select * from table name [where condition];

• Example:

  select * from test;

View part–> Basic syntax:

select field name[,field name] from table name[where Condition];

• Example:

  select name,age,grade from test where age = '18';

3 Update data

Basic syntax:

update table name set field = value [where condition];

• Example:

  update test set age = 20 where name = 'guo';

Here, it is recommended to add

where conditions as much as possible, Otherwise, the entire table data will be operated.

In addition, judging whether the update operation is successful does not depend on whether the SQL statement is executed successfully, but on whether any records are affected, that is, the number of

affected is greater than 1 when the update is truly successful.

4 Delete data

Basic syntax:

delete from table name [where condition];

• Example:

  delete from test where grade = '3.1';

Of course, we can also use

drop to implement the deletion operation, but Compared with delete, drop is more powerful. When performing a delete operation, it will not only delete data, but also delete definitions and release storage space; while delete When performing a delete operation, only the data will be deleted, and the definition and storage space will not be deleted.

Warm reminder: The contents enclosed by the symbols [] represent optional options; the symbols represent the meaning of connection.

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