ORDER BY

Sorts the result rows by one or more expressions, ascending or descending.

Syntax

ORDER BY expression [ASC | DESC] [NULLS FIRST | NULLS LAST], ...

ORDER BY is the only way to guarantee row order. It runs after SELECT, so it can use select-list aliases and column positions (ORDER BY 2).

ASC (default) sorts smallest first; DESC largest first. Each key has its own direction: ORDER BY category ASC, price DESC.
Later keys break ties in earlier ones. If the keys do not make every row unique, tied rows come back in an unpredictable order — add a unique column (usually the id) as the last key for a total order.
NULL: PostgreSQL treats NULL as larger than every value: NULLs come last in ASC and first in DESC. Override with NULLS FIRST / NULLS LAST.
You can sort by an expression not in the select list (ORDER BY lower(name)) except with SELECT DISTINCT.
Text sorts by the database collation; with ORDER BY name COLLATE "C" it sorts by byte value.

Two keys, mixed directions starter

SELECT category, product_name, price
FROM products
ORDER BY category, price DESC, product_id;

Categories A→Z; inside each category the most expensive first; product_id makes the order total.

Controlling where NULLs go starter

SELECT customer_name, email
FROM customers
ORDER BY email NULLS FIRST, customer_id;

Customers without an email appear first instead of last.

Sorting by an alias starter

SELECT order_id, quantity * 10 AS points
FROM orders
ORDER BY points DESC, order_id
LIMIT 5;

ORDER BY runs after SELECT, so the alias points is visible here (unlike in WHERE).

Leaving ties unresolved and then relying on the order (top-N lists, pagination, graded results).
Expecting DESC to put NULLs last: in PostgreSQL DESC puts NULLs first unless you add NULLS LAST.
Sorting numbers stored as text: '10' sorts before '9'. Cast to a number first.
Using an alias inside an expression in ORDER BY (ORDER BY points * 2): only a bare alias is allowed.

For orientation only: SQL Quest executes PostgreSQL.

MySQL: NULLs sort first in ASC (opposite of PostgreSQL) and there is no NULLS FIRST/LAST; use ORDER BY col IS NULL, col.
SQL Server: NULLs sort first in ASC; NULLS FIRST/LAST is not supported, use a CASE expression as the first key.
SQLite: NULLs sort first in ASC; NULLS FIRST/LAST is supported since 3.30.
Oracle: Same default as PostgreSQL (NULLs last in ASC) and supports NULLS FIRST/LAST.