MEPX
Chapter 2 of 10All chapters
  1. 1What SQL is
  2. 2SELECT and WHERE
  3. 3NULL
  4. 4Sorting and limiting
  5. 5Aggregates and GROUP BY
  6. 6Joins
  7. 7Keys and relationships
  8. 8Subqueries and CTEs
  9. 9Indexes and performance
  10. 10Changing data

Chapter 2 of 10

SELECT and WHERE

Choosing columns and filtering rows.

Picking columns

SELECT names the columns to return and FROM names the table. SELECT * returns everything, which is fine when exploring and wasteful in production code.

  • AS renames a column in the output, which matters for readability.
  • Expressions are allowed: SELECT price * quantity AS total.

Filtering

WHERE keeps only rows matching a condition, combined with AND, OR and NOT. IN checks a list, BETWEEN checks a range, and LIKE matches a text pattern.