How to query and update data in mysql

Mysql is a relational database management system that is widely used for server-side data storage and query. In actual applications, it is often necessary to query and update data through mysql. This article will introduce the basic usage and precautions of Mysql from two aspects: query and update.

1. Mysql query

The query statement of Mysql mainly includes the two keywords select and from. Select represents the fields and expressions that need to be queried, and from represents the data table to be queried. The specific syntax is as follows:

select field1, field2, ..., fieldN from table_name where condition;

Among them, field1, field2, ..., fieldN represents the list of fields to be queried, and the wildcard character * can be used to represent all fields. table_name represents the name of the data table, and condition represents the query condition. You can use the keywords and, or, etc. to combine multiple conditions.

For example, to query all records in a student table, you can use the following statement:

select * from student;

To query the name Zhang in the student table For records of three, you can use the following statement:

select * from student where name='Zhang San';

Query the students whose age is greater than 18 and whose gender is male in the student table The following statement can be used for recording:

select * from student where age>18 and gender='male';

In the query process, you can also use the aggregate function count , sum, avg, etc. to obtain statistical information, for example:

select count(*) from student;

The above statement can count the total number of records in the student table.

2. Mysql update

The update statement of Mysql mainly includes the two keywords update and set. Among them, update represents the data table that needs to be updated, and set represents the fields and values ​​that need to be updated. The specific syntax is as follows:

update table_name set field1=value1, field2=value2, ... where condition;

Among them, table_name represents the name of the data table that needs to be updated, field1, field2, ... represents the field list that needs to be updated, value1, value2, ... represents the value that needs to be updated, and condition represents the update condition.

For example, to update the scores of students aged 18 or younger in the student table to 60 points, you can use the following statement:

update student set score=60 where age<=18 ;

During the update process, you need to pay attention to the following matters:

1. Use where conditions to limit the range of updated records to avoid misoperations.
2. Before updating, you need to back up the data and conduct testing and verification.
3. You need to pay attention to data consistency and storage efficiency when updating.

3. Summary

Mysql is a powerful relational database management system that provides rich query and update functions. When using Mysql, you need to pay attention to the syntax of statements and the safety of operations. I hope that the introduction in this article can provide some reference and help for Mysql users.

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