Wich Preference is wrong (no replies)

My problem is probably because of the attitudes?!

For each block of code I have to open a new tab; the separation of the code blocks and their separate execution does not work.

An Example:

CREATE TABLE tier(
tiernumme int,
tiername varchar(225),
tierart varchar(225),
vorkommen varchar(50)
) ;

ALTER TABLE tier
ADD tierfarbe varchar(225);

generates the error message:

Error Code 1050: table "tier" already exists

Thanks for Your Support