Result Set of ONE to assign to a variable

[Sigifredo Gonzalez]

Hi Every one,

I'm creating INSERT, UPDATE, DELETE Triggers on a table CONTENT to make JSONs and update different rows from a table PRESENTATION. Those JSONs are huge strings of concatenations of data from the tables CONTENT and others.

What I do to create the the JSONs contents is make a strange and complex query that results in a long string.

The issue I'm having is that I can't assign the SELECT to a variable because I get this "ERROR 1242 (21000) at line 17: Subquery returns more than 1 row".

How can I do to make the variable assignation without having RESULT SET or SUBQUERY errors.

This is a shortened version of what I want to do.

set @super_long_string_json = ( SELECT CONCAT (a1, a2, a3, a4) as super FROM ( SELECT ...CONTENT ... ) as ALIAS );
UPDATE PRESENTATION set CONTENT = @super_long_string_json WHERE id = 1;

I have tried using GROUP by super, LIMIT 1 without a satisfactory result.

Thanks in advance,
Ziggy :-)