SQL SELECT & WHERE Cheat Sheet

SELECT: choose the columns

SELECT defines the shape of your result. Name the required columns explicitly in production queries instead of relying on SELECT *.

SELECT employee_id, employee_name, department, salary
FROM employees;

WHERE: filter rows

WHERE keeps rows that satisfy a condition. Text values use quotes; numeric values do not.

• Use AND when every condition must be true
• Use OR when at least one condition may be true
• Use parentheses when combining AND and OR

SELECT employee_name, salary
FROM employees
WHERE department = 'Engineering'
  AND salary >= 70000;

Handle NULL explicitly

NULL represents an unknown or missing value. Compare it with IS NULL or IS NOT NULL, not with the equals operator.

SELECT employee_name
FROM employees
WHERE manager_id IS NULL;

A reliable beginner workflow

Start with the table, select only the columns you need, add one filter at a time, run the query, and inspect whether edge cases such as NULL values behave as expected.