How to create a function SQL that returns a string from a table? - sql

Question

How can I create a function like this?
function FN_something (#entrada char(50))
declare #consulta table
declare #notificacao varchar(50)
declare #multa float
declare #saida varchar(50)
set #consulta as = (select num_notificacao,num_multa from table where field = #entrada)
set #notificacao = #consulta.num_notificacao
set #multa = #consulta.num_multa
set #saida = "resultado: "+ #notificacao +";"+#multa
return #saida
Thanks in advance

Answer 1

I would not use a function... Scalar functions tend to be a real performance killer. Try to use something like this inline
SELECT 'resultado: '
+ ISNULL(CAST(t.num_notificacao AS VARCHAR(MAX)),'???')
+ ';'
+ ISNULL(CAST(t.num_multa AS VARCHAR(MAX)),'???')
FROM SomeTable AS t WHERE t.SomeField=#entrada;
If you need a function it was much better to use an inlined TVF (syntax without BEGIN...END and bind it into your query with CROSS APPLY.
Might be simplified:
If your columns are NOT NULL you can go without ISNULL()-function. If your columns are strings, you can do without CAST()... My code is defensive proramming :-D
Hint
If this is something you need more often, you might introduce a VIEW carrying this calculated column and use it instead of your table. You might include this value into your table as computed column as well...
UPDATE
Great, the VIEW you show in the comment is an inline TVF actually, which is very good!
My magic crystall ball tells me, that you might need something like this:
SELECT cl.*
,'resultado: ' + t.num_notificacao + ';' + t.num_multa AS CalculatedResult
FROM dbo.[CampoLivre876]('SomeParameter') AS cl
LEFT JOIN SomeOtherTable AS t ON cl.entrada=t.SomeField --should be only one related row per main row!
This will call the iTFV and join it to the other Table, where the two columns are living. I Assume, that the CampoLivre876-row knows its entrada key.
Hint 2:
If this works for you, you might include this approach directly into your existing iTVF.
UPDATE 2
You might try to change your function like here:
ALTER FUNCTION [dbo].[CampoLivre876] ()
RETURNS TABLE
RETURN
Select cl.mul_numero_notificacao + ';' + CAST(cl.mul_valor_multa as varchar(max)) AS ExistingColumn
,'resultado: ' + t.num_notificacao + ';' + CAST(t.num_multa AS varchar(max)) AS CalculatedResult
From Campo_Livre AS cl With(NoLock)
INNER JOIN SomeOtherTable AS t ON cl.entrada=t.SomeField;
This should read all lines in one go. Reading 1 row after the other is - in almost all cases - something really, really bad...

Answer 2

Here is an example of a function with correct SQL Server syntax:
create function FN_something (
#entrada char(50) -- should probably be `varchar(50)` rather than `char(50)`
) returns varchar(50)
begin
declare #saida varchar(50);
select #saida = 'resultado: ' + num_notificacao + ';' + num_multa
from table
where field = #entrada;
return #saida;
end;
Note: This assumes that the num_ columns are strings, not numbers. If they are numbers, you need to convert them or use concat().
EDIT:
A function really isn't appropriate for this. Probably the best solution is a computed column:
alter table t add something as (concat('resultado: ', num_notificacao, ';', num_multa);
Then you can get the value directly from the table. In earlier versions of SQL Server, you would use a view rather than computed column.