What does on mean in sql

In SQL, ON is used to join rows in tables, specifying equal columns in different tables to match and combine rows.

The meaning of ON in SQL

In SQL, ON is used to specify rows in the connected table. It is used in JOIN operations where multiple tables are combined into a single result table.

The syntax of ON

<code>ON 表1.列名 = 表2.列名</code>

Where:

• Table 1 and Table 2 are the tables to be connected.
• The column name is the name of the equal column.

The role of ON

The ON clause determines which rows from different tables will be matched and combined. Only rows that meet the ON condition will be included in the result table.

Example

The following query uses the ON clause to connect the Customer table and the Order table, matching the customer ID (customer_id) column:

<code class="sql">SELECT *
FROM Customer
JOIN Order
ON Customer.customer_id = Order.customer_id;</code>

This The query returns a table with customer and order details, including only orders belonging to the same customer.

Note

The ON clause is an optional part of the JOIN operation. If omitted, an equijoin is used by default, where all rows that are equal will be matched.

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