SQL質疑応答スレ 18問目

[0046 NAME IS NULL 2018/02/22(木) 18:30:09.05 ID:???]

少し違うやり方だけどこっちのほうがパフォーマンスはいいかも。

SELECT c1, CASE sum(c3) WHEN 0 THEN sum(c2) ELSE 0 END
FROM (SELECT c1, c2, CASE WHEN c2 IS NULL THEN 1 ELSE 0 END AS c3 FROM t1) AS t2
GROUP BY c1
ORDER BY c1;