What does 'ALL' mean more?

In SQL, ALL is used in conjunction with comparison operators (>, <, >=, <=, =, <>) inside a subquery. It means that the WHERE condition will be true if the comparison is true for every value returned by the subquery.

Examples of usage:

• > ALL: the value is greater than the maximum value from the subquery.
• < ALL: the value is less than the minimum value from the subquery.
• = ALL: the value equals all values from the subquery (equivalent to = when there is exactly one value or an empty set, or always false when there are more than one unique values).

Example SQL query:

SELECT ProductName
FROM Products
WHERE Price > ALL (SELECT AveragePrice FROM Categories);

This query will return the names of products whose price is higher than the average price in all categories.