Querying with SELECT

SELECT retrieves data. Its basic form: SELECT attribute1, attribute2, ... FROM table_name WHERE condition;

• SELECT * (an asterisk instead of column names) shows all columns.
• Without WHERE, every row is shown. The book's examples use an EMPLOYEE table (EmpNo, Ename, Salary, Bonus, DeptId).

Column aliases with AS: SELECT Ename AS Name, Salary * 12 AS 'Annual Salary' FROM EMPLOYEE; renames the columns in the output only. An alias with a space must be in quotes. The alias does not add a column to the table.

DISTINCT removes repeated values from the output: SELECT DISTINCT DeptId FROM EMPLOYEE; lists each department once (5 departments in the book's table).

WHERE conditions:

• Relational operators: =, <, <=, >, >=, and != (not equal).
• Logical operators: AND (both true), OR (either true), NOT (reverses a condition). For example: WHERE Salary > 5000 AND DeptId = 'D04'; WHERE NOT DeptId = 'D03'.
• Text values in conditions go in quotes.

BETWEEN gives a range that includes both ends: WHERE Salary BETWEEN 20000 AND 50000 is the same as Salary >= 20000 AND Salary <= 50000.

Example (new): SELECT Ename, Salary FROM EMPLOYEE WHERE DeptId = 'D02' OR Salary < 15000; lists the names and salaries of everyone in department D02, plus anyone anywhere earning under 15000.