SQL ALL Keyword

 In SQL, the ALL keyword is used in conjunction with comparison operators to compare a value with a set of results returned by a subquery. It allows the comparison of a value to all values in the result set. It can be used with operators such as =, !=, >, <, >=, and <=.

Syntax:

SELECT column_name(s)
FROM table_name
WHERE expression operator ALL (subquery);

Key Points:

• The ALL keyword can be used with any comparison operator.
• It applies the comparison to all the results returned by the subquery.
• The subquery must return a result set for ALL to compare against.

Example Usage:

1. ALL with > (Greater than):

SELECT employee_name, salary
FROM employees
WHERE salary > ALL (SELECT salary FROM employees WHERE department = 'Sales');

This query retrieves the names and salaries of employees who earn more than everyone in the 'Sales' department.

2. ALL with = (Equal to):

SELECT product_name
FROM products
WHERE price = ALL (SELECT price FROM products WHERE category = 'Electronics');

This query retrieves the names of products that have the same price as all products in the 'Electronics' category.

How ALL works:

• The query will return the result only if the comparison is true for every value in the result set of the subquery.
• For example, if using > with ALL, the condition will only be true if the main query’s value is greater than every value returned by the subquery.

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