MEPX
Chapter 10 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 10 of 10

Changing data

INSERT, UPDATE, DELETE and transactions.

The dangerous clause

UPDATE and DELETE without a WHERE clause change every row in the table. Running the SELECT version of the condition first is a habit worth keeping for life.

  • A transaction groups statements so they all apply or none do.
  • COMMIT makes the change permanent; ROLLBACK undoes it.

Safety

Never build a query by joining strings with user input, which is how SQL injection happens. Use parameters and let the driver handle escaping.