I have tried a few tutorials but I do not think there is any expectation on how to declare the variable in select by MySQL,
DECLARE @idPedido INT;
DECLARE @idCombo INT;
SELECT @idPedido = idPedido, @idCombo = idCombo
FROM Pedidos
WHERE idCombo IS NOT NULL;
SELECT @idPedido;
SELECT @idCombo;
No MySql
Remembering that if SELECT has multiple results, it will only bring the last.
SELECT @idPedido := idPedido, @idCombo := idCombo
FROM Pedidos
WHERE idCombo IS NOT NULL;
SELECT @idPedido, @idCombo;
If you wanted a predefined variable, use SET :
SET @idPedido = 10;
SELECT @idPedido;
You're mixing everything.
To do select do so:
SELECT idPedido, idCombo
FROM Pedidos
WHERE idPedido = @idPedido AND idCombo = @idCombo
and to do update do so:
UPDATE Pedidos set idPedido = @idPedido, idCombo = @idCombo
WHERE id = 1
To do the select assigning the returned values to the variables do so:
DECLARE @idPedido INT;
DECLARE @idCombo INT;
SELECT idPedido, idCombo into @idPedido, @idCombo
FROM Pedidos
WHERE idCombo = 1;
Attention SELECT has to return 1 and only one line.