Some commonly used MySQL query commands

MySQL is a popular relational database management system that is widely used in web development and data storage. Queries are an important part of data retrieval and analysis using MySQL. The following are some commonly used MySQL query commands.

1. SELECT
   SELECT is the most commonly used MySQL query command. It is used to retrieve rows of data from a specified table and optionally select specific columns to return.

Syntax:

SELECT column_name(s) FROM table_name;

Select specific columns to return through the SELECT statement. The following is an example:

SELECT name, age FROM employee;

2. WHERE
   The WHERE command is used to filter data rows in the table that meet specified conditions.

Syntax:

SELECT column_name(s) FROM table_name WHERE condition;

The following is an example:

SELECT name, age FROM employee WHERE age > 30;

3. ORDER BY
   The ORDER BY command is used to perform a query on the result set based on specified conditions. Sort, by default in ascending order.

Syntax:

SELECT column_name(s) FROM table_name ORDER BY column_name ASC|DESC;

The following is an example:

SELECT name, age FROM employee ORDER BY age DESC;

4. GROUP BY
   The GROUP BY command is used to pair pairs based on one or more columns The result set is grouped to calculate the aggregate function. Aggregation functions are a set of built-in functions for summarizing data, such as COUNT, AVG, SUM, etc.

Syntax:

SELECT column_name(s) FROM table_name GROUP BY column_name;

The following is an example:

SELECT age, COUNT(*) FROM employee GROUP BY age;

5. JOIN
   The JOIN command is used to join two or more tables The data is combined into a result set.

Syntax:

SELECT column_name(s) FROM table_name1 JOIN table_name2 ON condition;

The following is an example:

SELECT employee.name, department.name FROM employee JOIN department ON employee.department_id = department.id;

6. DISTINCT
   The DISTINCT command is used to return the only different value in the result set.

Syntax:

SELECT DISTINCT column_name(s) FROM table_name;

The following is an example:

SELECT DISTINCT age FROM employee;

7. LIMIT
   The LIMIT command is used to limit the number of rows returned by the query.

Syntax:

SELECT column_name(s) FROM table_name LIMIT number;
SELECT column_name(s) FROM table_name LIMIT offset, number;

The first syntax is used to return the first n rows, and the second syntax is used to skip the first x rows and return n rows.

The following is an example:

SELECT name, age FROM employee LIMIT 10;
SELECT name, age FROM employee LIMIT 20, 10;

The above are some commonly used MySQL query commands. MySQL also provides many other commands, such as INSERT, UPDATE, DELETE, etc., which can be used for data manipulation and management. If you want to learn more about MySQL query commands, please refer to the MySQL documentation or attend a training course on the Internet.

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