Scriptorium mastered - summary

Wonderful, @name! You are leaving the Scriptorium a true master of filtering. You can now point the Library to exactly the scrolls you need - not a single one more.

What you have learned

• WHERE selects only the rows that satisfy a condition (always after

  FROM

  ).
• Comparison operators:

  =

  ,

  <>

  ,

  <

  ,

  >

  ,

  <=

  ,

  >=

  .
• We wrap text in single quotes

  ' '

  , but not numbers.
• AND - all conditions at once; OR - one is enough; NOT - negation.
• Parentheses

  ( )

  order things when we mix

  AND

  and

  OR

  .
• IN (...) - a list of allowed values (a shorter way of writing many

  OR

  ).
• BETWEEN a AND b - a range together with both ends.
• LIKE with the characters

  %

  (any sequence) and

  _

  (one character);

  NOT LIKE

  is the negation.
• IS NULL / IS NOT NULL - checking for emptiness (never

  = NULL

  !).

An example tying it all together

1SELECT * FROM ksiazki
2WHERE cena BETWEEN 20 AND 80
3  AND kategoria_id IN (1, 2)
4  AND tytul LIKE 'O%';

This query will return books priced from 20 to 80 coins, from category 1 or 2, whose title starts with O. Three conditions in one - the full power of the Scriptorium!

What's next?

In the next location you will learn to order results (

ORDER BY

) and limit their number (

LIMIT

), so that from the filtered pile of scrolls you can pick the most important ones. You already have the filter - now it is time to give it order. Onward, deeper into the Library, @name!