Return a value if no record is found

Question

I have this simple statement that works:

SELECT idnumber FROM dbo.database WHERE number = '9823474'

If the number does not exist anywhere in the table, it fails. I would like to add something to this statement that says:
IF NO RECORD IS FOUND RETURN NULL INSTEAD OF NO ROW.

Any suggestions?

Solution 1

Encapsulate the query in a sub-query to transform "no row" to a NULL value.

I tested and verified this with PostgreSQL, SQL Server and MySQL. Also works with SQLite.

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

In Oracle you have to select from the dummy 1-row table DUAL like this:

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

You can do the same in MySQL for compatibility reasons, but you don't have to.
Similar in Firebird:

SELECT (SELECT id FROM tbl WHERE id = 9823474) AS id FROM RDB$DATABASE;

This does it for DB2 (like Sean commented):

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

Alternative with UNION ALL

SELECT id FROM tbl WHERE id = 9823474
UNION  ALL
SELECT NULL -- FROM DUAL  -- for Oracle
FETCH FIRST 1 ROW ONLY;

Standard SQL, but I only tested this with Postgres, which evaluates like this:
If a row is found in the first SELECT, it is returned. Postgres stops looking for more rows, as soon as the first is found due to LIMIT 1 (FETCH FIRST 1 ROW ONLY).
The second SELECT is only even executed if the first returns nothing. The data type of the NULL value is determined by the data type of tbl.id automatically.

About the LIMIT clause:

• ANSI/ISO plans for LIMIT standardization?

Solution 2

To make it more simplier, this should work fine. If you assign this to a variable based on the datatype of your idnumber than you would be able to evaluate whether the value is null or the actual idnumber return.

SELECT ISNULL(
      (
         SELECT idnumber 
         FROM dbo.database 
         WHERE number = '9823474'
      ), NULL)

Solution 3

Select isnull(sum(Amount),0) as Amt from BeginningBalance where CustomerID = @CustomerID
Union all
Select isnull(sum(Amount),0) as Amt from SalesOrders where CustomerID = @CustomerID
Union all
Select isnull(sum(Amount),0) as Amt from SalesInvoices where CustomerID = @CustomerID
//Data Row Result if no data is present at Beginning Balance Table
// example 

Amt
2000  // amount from sales orders
1000  // amount from sales invoices

---

// if the 1st select statement return no data use this
SELECT (select sum(Amount) from BeginningBalance 
        where CustomerID = @CustomerID) as Amt
Union all
Select sum(Amount) as Amt from SalesOrders where CustomerID = @CustomerID
Union all
Select sum(Amount) as Amt from SalesInvoices where CustomerID = @CustomerID

Result :

Amt
NULL  // amount from BeginningBalance
2000  // amount from sales orders
1000  // amount from sales invoices

Solution 4

I use this for MySql

SELECT IFNULL(ColumnA,"1") AS ColumnA , COUNT(1) AS Total FROM table 
WHERE ID = 1 LIMIT 0, 1;

Solution 5

Simplest way for me was to use the good old IF THEN ELSE trick! Works with all SQL flavors.

IF EXISTS (SELECT * FROM dbItem WHERE price >= 10)
BEGIN
    SELECT * FROM dbItem WHERE price >= 10
END
ELSE
  SELECT 'No record'

View more solutions

Comments

[Lightness Races in Orbit]

Give it that value in what row? There are no rows in which to give it a value.

[Valentin Despa]

Works well in Firebird. Thanks for doing the research.

[8.8.8.8]

I do not understand why sub-query encapsulation works.

[Erwin Brandstetter]

@8.8.8.8: Because "no row" from a subquery is converted to a NULL value in the SELECT list. It's a logic necessity.

[chrismarx]

I'm surprised there isn't a function to do this. But this definitely works

[Erwin Brandstetter]

@chrismarx: If your query returns no row (nothing at all), there is no place for a function to catch that. So we need an outer SELECT - and then we don't even need a function.

[Sean Branchaw]

This works in DB2 as well, provided you substitute DUAL with SYSIBM.SYSDUMMY1.

[Mohit Atray]

What if I want to return 0 instead of null when no row is found?

[Erwin Brandstetter]

@MohitAtray: Use COALESCE. As in: SELECT COALESCE((SELECT ...), 0) AS id; And it's easy with the UNION variant.

[Max Hodges]

PostgreSQL does not have the ISNULL function.