How to use square brackets in mysql

MySQL square brackets have three main uses: 1. Identifier escaping; 2. Subquery; 3. Priority control, expressions within brackets are evaluated first.

Usage of brackets in MySQL

There are three main uses of brackets in MySQL:

1. Identifier escaping

When the identifier (table name, column name, etc.) contains spaces or special characters, you can use backticks (``) to enclose it. This helps ensure that MySQL interprets identifiers correctly.

For example:

<code>SELECT * FROM `My Table`;</code>

2. Subquery

Parentheses (()) are used to contain subqueries, that is, nested in the main query query. The results of the subquery are used as values ​​or conditions in the main query.

For example:

<code>SELECT * FROM users WHERE name IN (
  SELECT name FROM other_users
  WHERE age > 30
);</code>

3. Priority control

Parentheses can also be used to control the priority of operators. The expression inside the operator is evaluated first, then the expression outside the parentheses.

For example, the following query will evaluate the addition expressions in parentheses first, and then the multiplication expressions:

<code>SELECT 10 * (5 + 2);  -- 结果为 70</code>

It should be noted that the precedence rules give priority to the order of operators, followed by are brackets. For example, the multiplication operator has higher precedence than the addition operator, even if the addition expression inside the parentheses is evaluated first:

<code>SELECT 10 * (5 + 2);  -- 结果为 90</code>

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