IF EXISTS (SELECT 1 FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME = 'JetPrint')
BEGIN
    IF NOT EXISTS
    (
        SELECT COLUMN_NAME
        FROM INFORMATION_SCHEMA.COLUMNS
        WHERE TABLE_NAME = 'JetPrint'
              AND COLUMN_NAME = 'WarehouseCode'
    )
    BEGIN
        ALTER TABLE JetPrint ADD WarehouseCode VARCHAR(5) NULL;
    END
END