What does using mean in sql

The USING keyword in SQL is used to connect tables and specify the connection conditions by specifying a column participating in the connection. It only allows joining tables by one column, so it provides a concise and readable syntax when a JOIN condition involves a column.

The meaning of USING in SQL

In SQL, the USING keyword is used to join tables, especially in In a JOIN operation, it specifies the columns participating in the join.

Usage

The syntax of the USING clause is as follows:

SELECT ...
FROM table1
JOIN table2
USING (column_name)

Among them:

• table1 and table2 are the tables to be joined.
• column_name is the column name to be used when connecting the two tables.

Role

The role of the USING clause is to specify the join condition, which joins the tables by matching specified columns with the same value in the two tables. This means that the specified column is a primary or unique key in both tables.

Example

For example, the following query uses the USING clause to join the Customers table and the Orders table, and customer_id column is used as a join condition:

SELECT *
FROM Customers
JOIN Orders
USING (customer_id)
WHERE customer_name = 'John Doe';

Differences from the ON clause

The USING clause is very similar to the ON clause, they both Used to specify JOIN conditions. However, there is one major difference with the USING clause:

• The USING clause only allows joining tables by one column, while the ON clause can join tables by multiple expressions.

The USING clause can provide a cleaner, more readable syntax when the JOIN condition involves a column.

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