Mysql : Not allowed to return a result set from a function

Question

I have write one function but getting this error Not allowed to return a result set from a function

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Answer 1

Mysql complains about SELECT statement in your function,

probably it understands SELECT p_KeyValue = ListName + '.' + Value as comparison

change it to

SELECT CONCAT(ListName, '.', Value) INTO p_KeyValue

Answer 2

You want to assign the result of a query to a variable, but in fact you're just selecting. That's why MySQL's complaining.

You have to change this

            SELECT  p_KeyValue = ListName + '.' + Value
            FROM ListsTable
            WHERE EntryID = p_ParentID  LIMIT 1 ;

to

            SELECT CONCAT(ListName, '.', `Value`)
            INTO p_KeyValue
            FROM ListsTable
            WHERE EntryID = p_ParentID  LIMIT 1 ;

And you should add an ORDER BY. A LIMIT without ORDER BY doesn't make sense, since there's no guaranteed order in a relational database.