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