Instead of MySQL's IFNULL function, this works on PostgreSQL, Sqlite and others too

Code
SELECT price FROM history
    WHERE id <= 20
    ORDER BY price;

SELECT COALESCE(price, 0) AS price FROM history
    WHERE id <= 20
    ORDER BY price;
Result
price
null
null
null
11.866840
165.719980
220.130140
255.304260
447.617910
555.924660
557.201690
592.212810
694.705850
720.863290
728.519790
758.528980
817.706430
855.565560
915.765130
935.217710
955.729040
0.0011458396911621 ms (with caching enabled)

price
0.000000
0.000000
0.000000
11.866840
165.719980
220.130140
255.304260
447.617910
555.924660
557.201690
592.212810
694.705850
720.863290
728.519790
758.528980
817.706430
855.565560
915.765130
935.217710
955.729040
0.00061202049255371 ms (with caching enabled)