MySQL: Explain ALL operator in MySQL.

 

In MySQL, the ALL operator is used in conjunction with a comparison operator and a subquery. It compares a value to all values returned by the subquery. The ALL operator returns true if the specified condition is true for all the values in the result set of the subquery.

The basic syntax of ALL is as follows:

sql
expression OPERATOR ALL (subquery)

Here, expression is the value to compare, OPERATOR is a comparison operator (e.g., =, <, >, etc.), and subquery is a subquery that returns a set of values.

For example, let's say you want to find all records from the sales table where the amount is greater than all amounts in the target_sales table:

sql
SELECT *
FROM sales
WHERE amount > ALL (SELECT target_amount FROM target_sales);

In this example, the subquery (SELECT target_amount FROM target_sales) returns a set of target amounts, and the amount > ALL condition checks if the amount in the sales table is greater than all values in the set returned by the subquery.

It's important to note that the ALL operator is often used with comparison operators such as =, <, >, <=, >=, etc. It provides a way to compare a value against all values in a set and is particularly useful when you want to ensure that the condition holds true for every element in the result set of the subquery.

Here's an alternative way to write the same query using the MAX() function:

sql
SELECT *
FROM sales
WHERE amount > (SELECT MAX(target_amount) FROM target_sales);

Both queries are equivalent, and you can choose the syntax that you find more readable or suitable for your specific use case.