EXISTS Operator in SQL - Quick Tip
- Saturday, September 21, 2019
- By Ravinder Sharma
- 1 Comments
EXISTS Operator in SQL - Quick Tip
The EXISTS operator is used to check the existence, it is a logical operator that returns true or false only.
We can use them within IF or Sub Queries.
USING WITH IF :
IF EXISTS (
SELECT [ COLUMN_NAME ]
FROM [ TABLE_NAME ]
WHERE [ COLUMN_NAME ] IS NOT NULL
)
BEGIN
--QUERY TO DO ( SELECT [ID]
FROM [TABLE_NAME] WHERE [ COLUMN_NAME ] IS NOT NULL)
END
USING WITH SUB QUERY :
SELECT [ID]
FROM [TABLE_NAME]
WHERE EXISTS (
SELECT [ COLUMN_NAME ]
FROM [ TABLE_NAME ]
WHERE [ COLUMN_NAME ] IS NOT NULL
)
Note: when we are using EXISTS operator in sub query, it will return true even when the sub query return NULL, as showing below in example :
SELECT [ COLUMN_NAME ]
FROM [ TABLE_NAME ]
WHERE EXISTS (
SELECT NULL
)
In the above query EXISTS will return true and query will return all data without any condition or filter.
