Also what will be the scenarios where this query is used
select * from TableA where exists
(select null from TableB where TableB.Col1=TableA.Col1)
Also what will be the scenarios where this query is used select * from
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Also what will be the scenarios where this query is used
select * from TableA where exists
(select null from TableB where TableB.Col1=TableA.Col1)
The EXISTS condition is considered “to be met” if the subquery returns at least one row.
The syntax for the EXISTS condition is:
SELECT columns
FROM tables
WHERE EXISTS ( subquery );
Please note that “Select Null from mytable” will return number of rows in mytable but all will contain only one column with null in the cell as the requirement of outer query is just to check whether any row fall in the given given condition like in your case it is “TableB.Col1=TableA.Col1”
you can change null to 1, 0 or any column name available in the table. 1/0 may not be a good idea 🙂