The meaning of in in sql

The IN operator in SQL is used to check whether a value belongs to a list of specified values. It can: Check multiple values ​​Optimize performance Improve readability

IN operator in SQL

Meaning:

IN operator is used to check whether a value belongs to the list of specified values.

Syntax:

<code>SELECT column_name
FROM table_name
WHERE column_name IN (value1, value2, ...);</code>

Usage:

IN operator can be used in the following scenarios:

• Checking multiple values: If you want to check whether a value belongs to a series of values, you can use the IN operator.
• Optimize performance: Compared to using multiple OR conditions, the IN operator can optimize performance, especially when checking a large number of values.
• Improve readability: Use the IN operator to make queries more readable and easier to understand.

Example:

<code>-- 检查客户 ID 是否在 1、2 和 3 中
SELECT customer_id
FROM customers
WHERE customer_id IN (1, 2, 3);</code>

Note:

• The list of values ​​in the IN operator must be enclosed in parentheses.
• The values ​​in the value list can be constants, column names, or subqueries.
• The IN operator is case-sensitive, so you need to be careful when specifying values.
• The IN operator returns FALSE if the list of values ​​is empty.

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