How Can I Return NULL Instead of a Row-Not-Found Error in SQL Queries?

Returning NULL When No Records Found

When using SQL to retrieve data from a database, it's common to encounter situations where the desired record may not exist. By default, such situations result in a row-not-found error. However, there are ways to handle this and return a specific value instead.

Subquery Encapsulation

A simple yet effective method to return a null value when no record is found is to encapsulate the query in a subquery. This technique transforms the "row-not-found" error into a null value.

Here's an example:

SELECT (SELECT idnumber FROM dbo.database WHERE number = '9823474') AS idnumber;

Compatibility Considerations

This method has been tested and verified to work in PostgreSQL, SQLite, SQL Server, MySQL, and Firebird. However, slight variations may be necessary for other database systems.

For instance, in Oracle, it's necessary to query from a dummy 1-row table called DUAL:

SELECT (SELECT id FROM tbl WHERE id = 9823474) AS id FROM DUAL;

DB2 requires a similar approach, using SYSIBM.SYSDUMMY1 as the dummy table:

SELECT (SELECT id FROM tbl WHERE id = 9823474) AS id FROM SYSIBM.SYSDUMMY1;

By encapsulating the query in a subquery, you can effectively handle the absence of records and return a null value instead of facing a row-not-found error.

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