---

Nested queries

---

• Nested Queries
  • Nested query:

    A nested query is a SELECT query where the WHERE clause contains subquery.

  • Schematically:

    SELECT ... FROM ... WHERE ... (SELECT ... /* Subquery */ FROM ... WHERE ...)

    ---

    ---

    ---

    ---

  • In theory, nesting can be arbitrarily deep :

    SELECT ... FROM ... WHERE ... (SELECT ... FROM ... WHERE ... (SELECT ... FROM ... WHERE ...)

  • In practice, depending on your DBMS system, the number of nesting levels is limited (and different for each system)

    According to click here, MySQL can have 60 levels of nested selects.