Returning a value even if no result

Question

I have this kind of simple query that returns a not null integer field for a given id:

SELECT field1 FROM table WHERE id = 123 LIMIT 1;

The thing is if the id is not found, the resultset is empty. I need the query to always return a value, even if there is no result.

I have this thing working but I don't like it because it runs 2 times the same subquery:

SELECT IF(EXISTS(SELECT 1 FROM table WHERE id = 123) = 1, (SELECT field1 FROM table WHERE id = 123 LIMIT 1), 0);

It returns either field1 if the row exists, otherwise 0. Any way to improve that?

Thanks!

Edit following some comments and answers: yes it has to be in a single query statement and I can not use the count trick because I need to return only 1 value (FYI I run the query with the Java/Spring method SimpleJdbcTemplate.queryForLong()).

Answer 1

MySQL has a function to return a value if the result is null. You can use it on a whole query:

SELECT IFNULL( (SELECT field1 FROM table WHERE id = 123 LIMIT 1) ,'not found');

Answer 2

As you are looking for 1 record, (LIMIT 1) then this will work.

(SELECT field1 FROM table WHERE id = 123) 
UNION 
(SELECT 'default_value_if_no_record')
LIMIT 1;

Can be a handy way to display default values, or indicate no results found. I use it for reports.

See also http://blogs.uoregon.edu/developments/2011/03/31/add-a-header-row-to-mysql-query-results/ for a way to use this to create headers in reports.

Answer 3

You could include count(id). That will always return.

select count(field1), field1 from table where id = 123 limit 1;

http://sqlfiddle.com/#!2/64c76/4