SELECT, WHERE and ORDER BY

Tables, rows and columns, and how to pick and filter them.

A relational database stores data in tables: each row is a record, each column is a field. SQL (Structured Query Language) is how you ask questions. Examples use this table, users:

Read data

SELECT name, age FROM users;                       -- chosen columns
SELECT * FROM users;                               -- every column
SELECT * FROM users WHERE country = 'US';          -- filter rows
SELECT * FROM users WHERE age >= 30 AND country <> 'ES';
SELECT * FROM users ORDER BY age DESC;             -- sort, highest first
SELECT * FROM users ORDER BY age DESC LIMIT 2;     -- only the first 2

Useful filters

• IN ('US','IE') matches any value in a list.
• BETWEEN 30 AND 40 matches an inclusive range.
• LIKE 'A%' matches text starting with A (% is any characters).
• IS NULL finds missing values: = NULL never matches.

NoteText values use single quotes. Double quotes are for identifiers in standard SQL.