Some minor omissions can go unnoticed and produce completely unexpected results.
The following code example has two seemingly similar SELECT statements but they produce different results. All because I missed out a comma in the second SELECT statement! SQL Server did not raise any error and quietly assumed that I have tried to use an alias name for the First Name column!
CREATE TABLE employee ( employee_id INT, firstname VARCHAR(50), middleinitial VARCHAR(1), lastname VARCHAR(50) ) INSERT INTO employee (employee_id, firstname, middleinitial, lastname) VALUES (1001, 'Timothy', 'B', 'Parker'), (1002, 'Henry', 'F', 'Williams'), (1003, 'Jeff', NULL, 'Smith'), (1004, 'Mary', 'M', 'Marsh'), (1005, 'Miles', 'V', NULL) --Correct statement SELECT employee_id, firstname, middleinitial, lastname FROM employee -- Wrong statement with a comma missing -- between the firstname and middleinitial columns. -- SQL Server thinks it is an alias for firstname. SELECT employee_id, firstname middleinitial, lastname FROM employee
