NULL в SQL
SELECT 1 + NULL, CONCAT(1, NULL), CONCAT_WS(',', 1, NULL), AVG(v), COUNT(*), MIN(v) FROM (SELECT 1 AS v UNION ALL SELECT NULL AS v) AS t1;
В виде текста:
+----------+-----------------+-------------------------+--------+----------+--------+ | 1 + NULL | CONCAT(1, NULL) | CONCAT_WS(',', 1, NULL) | AVG(v) | COUNT(*) | MIN(v) | +----------+-----------------+-------------------------+--------+----------+--------+ | NULL | NULL | 1 | 1.0000 | 2 | 1 | +----------+-----------------+-------------------------+--------+----------+--------+