sql - How to select an empty result set?

Sql - How to select an empty result set?

If you want to select an empty result set in SQL, you can use a condition that is always false. Here's an example:

SELECT * FROM your_table WHERE 1 = 0;

In this query, 1 = 0 is a condition that is never true, so the result set will always be empty. Replace your_table with the actual name of the table you are working with.

Alternatively, you can use a similar approach with NULL:

SELECT * FROM your_table WHERE NULL;

This condition will also result in an empty result set.

Both of these queries essentially create a condition that is impossible to satisfy, ensuring that the query returns no rows.

Examples

  1. Selecting No Rows from a Table:

    • SELECT * FROM YourTable WHERE 1 = 0;
    • Description: Uses a condition that is always false (1 = 0) to ensure that no rows are selected from the table.

  2. Using a Subquery with LIMIT 0:

    • SELECT * FROM YourTable WHERE 1 = (SELECT 1 LIMIT 0);
    • Description: Utilizes a subquery with LIMIT 0 to ensure that the subquery returns no rows, resulting in an empty result set.

  3. Selecting Rows Based on a False Condition:

    • SELECT * FROM YourTable WHERE 1 = 2;
    • Description: Uses a condition that is always false (1 = 2) to filter out all rows from the table.

  4. Using a Common Table Expression (CTE) with WHERE 1 = 0:

    • WITH EmptyCTE AS ( SELECT * FROM YourTable WHERE 1 = 0 ) SELECT * FROM EmptyCTE;
    • Description: Creates a Common Table Expression (CTE) with a condition that is always false and then selects from the CTE.

  5. Selecting from an Empty Temporary Table:

    • CREATE TEMPORARY TABLE EmptyTempTable AS SELECT * FROM YourTable WHERE 1 = 0; SELECT * FROM EmptyTempTable;
    • Description: Creates an empty temporary table using a false condition and then selects from that temporary table.

  6. Using EXISTS with a False Subquery:

    • SELECT * FROM YourTable WHERE NOT EXISTS (SELECT 1 WHERE 1 = 1);
    • Description: Utilizes the EXISTS clause with a subquery that is always false to ensure an empty result set.

  7. Selecting from an Empty Table Variable:

    • DECLARE @EmptyTable TABLE (Column1 INT); SELECT * FROM @EmptyTable;
    • Description: Declares an empty table variable and then selects from that table variable.

  8. Using MIN/MAX with a False Condition:

    • SELECT MIN(Column1) FROM YourTable WHERE 1 = 0;
    • Description: Applies an aggregate function (MIN or MAX) with a condition that is always false to ensure no rows are selected.

  9. Selecting Rows Based on an Impossible Condition:

    • SELECT * FROM YourTable WHERE NULL = 'ImpossibleValue';
    • Description: Uses an impossible condition (NULL = 'ImpossibleValue') to filter out all rows from the table.

  10. Using a Filtered Aggregate with GROUP BY:

    • SELECT Column1, COUNT(*) FROM YourTable WHERE 1 = 0 GROUP BY Column1;
    • Description: Applies a filtered aggregate (COUNT) with a condition that is always false along with GROUP BY to create an empty result set.

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