yzn https://blog.hatena.ne.jp/yzn/ yzn’s memo https://yzn.hatenadiary.org/ dev MySql SELECT t1.key, t1.count, t2.count, t3.count, t4.count FROM table01 AS t1 LEFT OUTER JOIN table02 AS t2 ON (t1.key = t2.key) LEFT OUTER JOIN table03 AS t3 ON (t1.key = t3.key) LEFT OUTER JOIN table04 AS t4 ON (t1.key = t4.key) ; table01 に対して外部結合を行うので、table01 にしか存在しない key の場合、 key999 NULL NULL NULL NU… 190 <iframe src="https://hatenablog-parts.com/embed?url=https%3A%2F%2Fyzn.hatenadiary.org%2Fentry%2F20061029%2Fp1" title=" MySql で複数テーブルの外部結合(OUTER JOIN) - yzn’s memo" class="embed-card embed-blogcard" scrolling="no" frameborder="0" style="display: block; width: 100%; height: 190px; max-width: 500px; margin: 10px 0px;"></iframe> Hatena Blog https://hatena.blog 2006-10-29 00:00:00 rich https://yzn.hatenadiary.org/entry/20061029/p1 1.0 100%