The difference between = and in in mysql

In MySQL, the "=" operator compares two values ​​for equality, while the "IN" operator checks whether a value is contained in a list of values. The "=" operator only compares two values, while the "IN" operator can compare one value with multiple values ​​at a time. The "=" operator generally performs better than the "IN" operator and should be preferred if possible.

The difference between "=" and "IN" in MySQL

In MySQL, the difference between "=" and " IN" are both operators used to compare values. However, they work differently.

"=" Operator

"=" Operator is used to compare two values ​​for equality. If equal, returns TRUE; otherwise, returns FALSE. For example:

<code class="sql">SELECT * FROM users WHERE username = 'john';</code>

This will return all users with the username "john".

"IN" operator

The "IN" operator checks whether a value is contained in a list of values. Returns TRUE if included; otherwise, returns FALSE. For example:

<code class="sql">SELECT * FROM users WHERE username IN ('john', 'jane', 'bob');</code>

This will return all users with the username "john", "jane" or "bob".

Main difference

The "=" operator only compares two values, while the "IN" operator can compare one value with multiple values. Therefore, the "IN" operator is often used to check whether a value belongs to a known set of values.

Performance considerations

The "=" operator performs better than the "IN" operator. This is because the "IN" operator needs to traverse the list of values, while the "=" operator does not. Therefore, the "=" operator should be preferred if possible.

Example

The following are examples of "=", "IN" and "=" combined with "IN":

<code class="sql">-- 使用 "=" 比较两个值
SELECT * FROM users WHERE username = 'john';

-- 使用 "IN" 比较一个值与多个值
SELECT * FROM users WHERE username IN ('john', 'jane', 'bob');

-- 使用 "=" 和 "IN" 组合
SELECT * FROM users WHERE username = 'john' OR username IN ('jane', 'bob');</code>

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