Back to the Gate - SELECT, WHERE, ORDER BY

Before we reach for the hardest tricks, let us return to the fundamentals. Every great query begins with three simple tools: selection, filter and order.

SELECT - what we want to see

SELECT

names the columns, and

FROM

names the shelf we read from:

1SELECT tytul, cena FROM ksiazki;

WHERE - filtering rows

WHERE

lets through only the rows that meet a condition. We can use the operators

=

,

>

,

<

,

>=

,

<=

,

<>

:

1SELECT tytul, cena FROM ksiazki WHERE dostepna = 1;

This question returns only books that are on the shelf.

ORDER BY - sorting results

ORDER BY

arranges results by a chosen column.

ASC

is ascending order (the default),

DESC

is descending:

1SELECT tytul, cena FROM ksiazki ORDER BY cena DESC;

LIMIT - only the top

LIMIT

restricts the number of returned rows. Together with sorting it produces rankings:

1SELECT tytul, cena FROM ksiazki ORDER BY cena DESC LIMIT 3;

This query shows the three most expensive books in the Library. Filter, order and limit - the everyday tools of every scribe!