MySql で複数テーブルの外部結合(OUTER JOIN)
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 NULL
となる