What does using mean in sql

Usage of USING in SQL

USING in SQL is a keyword used to specify the connection relationship between tables. It allows you to join multiple tables together to extract data from different tables.

Syntax

<code>SELECT 列名
FROM 表名1
USING (连接列名)
JOIN 表名2</code>

Parameters

• Column name:The column to be retrieved name.
• Table name 1: The first table to be connected.
• Table name 2: The second table to be connected.
• Connection column name: The name of the column that connects the two tables. The join column names in both tables must be of the same type.

How to use

1. Determine the joining columns:Determine the columns to be joined in the two tables.
2. Use the USING clause: Use the USING clause in the JOIN statement to specify the connection column.
3. Specify the table name: Specify the table name to be connected in the USING clause.

Example

<code>SELECT *
FROM customers
USING (customer_id)
JOIN orders</code>

This query will join the customers table and orders table, using the customer_id column as the join column.

Advantages

• Simplified queries: The USING clause makes it easier to join multiple tables, especially when joining column names under the same circumstances.
• Improving performance: In some cases, the USING clause can improve query performance because the SQL optimizer can use it to generate a more efficient query plan.

Note

• The USING clause can only be used to join two tables.
• Joining columns must have the same data type.
• Table names cannot be repeated in the USING clause.

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