Usage of using in sql

The USING clause in SQL is used to connect tables. It specifies the columns used to connect records. It can be used for inner joins, outer joins, cross joins, etc. It can improve query simplicity, readability and performance. .

Usage of USING clause in SQL

In SQL, the USING clause is used to connect two or Multiple tables and specify the columns used to join records in the tables. It is mainly used for inner joins, but can be used for other types of joins as well.

Inner join

Inner join is the most common way to use the USING clause. It only returns records that exist in all joined tables.

Syntax:

<code class="sql">SELECT *
FROM table1
INNER JOIN table2 ON table1.column_name = table2.column_name</code>

For example, to join the "customers" and "orders" tables, use the following query:

<code class="sql">SELECT *
FROM customers
INNER JOIN orders ON customers.customer_id = orders.customer_id</code>

This will only return records for customers who have orders.

Other connection types

The USING clause can also be used for other types of connections, such as:

• OUTER JOIN (LEFT JOIN, RIGHT JOIN, FULL JOIN)
• Cross join (CROSS JOIN)

Usage advantages

Using the USING clause has the following advantages:

• Succinctness: It eliminates the need to use the ON clause to specify join conditions, making the query more concise.
• Readability: It improves the readability of the query by explicitly specifying the columns used for the join.
• Performance: In some cases, the USING clause can improve performance because it allows the optimizer to use a more efficient join method.

Notes

When using the USING clause, you need to pay attention to the following:

• Make sure that the connection is listed in all participating They all exist in the table and have the same data type.
• If the join column contains null values, the USING clause will ignore these records.
• The USING clause cannot be used with the WHERE clause to further filter the concatenated results.

The above is the detailed content of Usage of using in sql. For more information, please follow other related articles on the PHP Chinese website!