What operations can be followed by where in sql?

The WHERE clause uses operators to filter database records based on conditions, including comparisons (=, <>, >, <, >=, <=), logic (AND, OR, NOT ), Boolean (TRUE, FALSE, NULL), range (BETWEEN, IN), string (LIKE, NOT LIKE) and other operators (IS NULL, IS NOT NULL, EXISTS, NOT EXISTS).

Operators after the WHERE clause in SQL

The WHERE clause is used to filter the database according to specified conditions records in the table. It supports the use of a wide range of operators to compare field values ​​and determine which records to retain.

Comparison operators

• Equal to (=)
• Not equal to (<> or !=)
• Greater than (>)
• Less than (<)
• Greater than or equal to (>=)
• Less than or equal to (<=)

Logical operators

• AND (AND): Returns records that meet both conditions.
• Or (OR): Return records that meet any one condition.
• Not (NOT): Return records that do not meet the specified conditions.

Boolean operators

• True (TRUE): Returns a true value.
• FALSE (FALSE): Returns a false value.
• Unknown (NULL): Indicates that the value is unknown or does not exist.

Range operator

• BETWEEN: Returns records within the specified range.
• IN: Returns records whose values ​​are in the specified list.

String operators

• LIKE: Returns records matching the specified pattern.
• NOT LIKE: Returns records that do not match the specified pattern.
• %: wildcard character, representing any sequence of characters.
• _: Wildcard character, representing any single character.

Other operators

• IS NULL: Returns records with NULL value.
• IS NOT NULL: Returns records whose value is not NULL.
• EXISTS: Returns true when the subquery returns at least one record.
• NOT EXISTS: Returns true when the subquery does not return any records.

Usage example

SELECT * FROM users WHERE id = 1; -- 使用等于运算符
SELECT * FROM orders WHERE total > 100; -- 使用大于运算符
SELECT * FROM products WHERE category = 'Electronics' OR category = 'Gadgets'; -- 使用或运算符
SELECT * FROM customers WHERE name LIKE '%John%'; -- 使用 LIKE 运算符
SELECT * FROM posts WHERE created_at BETWEEN '2023-01-01' AND '2023-12-31'; -- 使用 BETWEEN 运算符
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