What does using mean in sql

The USING keyword is used in SQL to join tables with common columns. Its main functions include: Joining tables: USING can join two or more tables to query or operate their data. Specify join conditions: USING allows you to specify join conditions that compare values ​​in common columns to determine which rows to join.

The meaning of USING in SQL

The USING keyword is used in SQL to connect tables and specify connection conditions . Its main function is:

Connecting tables

USING is mainly used to connect tables with common columns. It allows you to join two or more tables together in order to query or manipulate their data.

Grammar

The basic form of USING grammar is:

<code class="sql">SELECT column_list
FROM table1
INNER JOIN table2
USING (common_column)</code>

where:

• table1 and table2 are to be connected The table
• common_column is a common column with the same data type in both tables
• INNER JOIN specifies the inner join type and returns only records of rows with matching values

Join conditions

The USING keyword can specify join conditions to determine which rows to join. It is essentially a shorthand form of the WHERE clause, which is used to compare values ​​in a common column.

Example

For example, consider the following Customer and Order tables:

<code class="sql">CREATE TABLE Customer (
  customer_id INT PRIMARY KEY,
  name VARCHAR(255)
);

CREATE TABLE Order (
  order_id INT PRIMARY KEY,
  customer_id INT,
  product VARCHAR(255),
  quantity INT,
  FOREIGN KEY (customer_id) REFERENCES Customer(customer_id)
);</code>

To select data from these two tables, you can use the USING join :

<code class="sql">SELECT *
FROM Customer
INNER JOIN Order
USING (customer_id)
WHERE quantity > 5;</code>

This query will return all customer and order records with a purchase quantity greater than 5.

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