How to perform data query in mysql

We have learned about the addition, deletion, modification and query operations of the database before, but we only have a simple understanding of the query operations of the database. Let's follow the editor to learn other operations of database query records.

First we create a data table students. This operation is based on this data table. The data of this data table is as follows:

1. Query records

select distinct 字段1,字段2 from 表名;

Among them:

• field: refers to the field that needs to be queried, such as in the data table id or age;

• Table name: It is the data table we operate on, for example, I am operating the table students;

As long as any field between field 1 and field 2 is different, it will be selected. It is generally used for distinct to filter only one field;

At the same time, this statement can also be used for a certain Query under these conditions, conditional query comparison symbols: ,,<code>>,<code>>=, ,<code>!= and other comparison operators, you can use or and and other ## between multiple conditions #You can use in this statement.

You can see the example:

2. Sorting

You can use sql statements Sort the data in ascending and descending order.

Ascending order:

select * from 表名 order by 字段名 asc;

Descending order:

select * from 表名 order by字段名 desc;

In sql,

the default is ascending order when sorting.

3. Limitation

Add

limit at the end of the statement Number 1, number 2<strong></strong> are used to limit the number of queries. The number 1 represents which record to start fetching (starting from 0), and the number 2 represents how many records to fetch!

If only the number 1 is written after

limit, then one record will be taken by default.

4. Aggregation

Users need to perform some summary operations, which requires sql aggregation operations.

select sum(字段名) from 表名;

The sum of data can be achieved through sum.

select count(*|字段名) from 表名;

The counting of fields can be completed through count. The counting results of using * or field names are the same.

select max(字段名) from 表名;

max can find the maximum value in the data. In this data table, the maximum value is 40, so the output result is 40.

select min(字段名) from 表名;

min can find the minimum value in the data. In this data table, the minimum value is 10, so the output result is 10.

Recommended tutorial: mysql video tutorial

The above is the detailed content of How to perform data query in mysql. For more information, please follow other related articles on the PHP Chinese website!