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IS_OUTER_JOIN是啥？

/* * OUTER joins are those for which pushed-down quals must behave differently * from the join's own quals.  This is in fact everything except INNER and * SEMI joins.  However, this macro must also exclude the JOIN_UNIQUE symbols * since those are temporary proxies for what will eventually be an INNER * join. * * Note: semijoins are a hybrid case, but we choose to treat them as not * being outer joins.  This is okay principally because the SQL syntax makes * it impossible to have a pushed-down qual that refers to the inner relation * of a semijoin; so there is no strong need to distinguish join quals from * pushed-down quals.  This is convenient because for almost all purposes, * quals attached to a semijoin can be treated the same as innerjoin quals. */#define IS_OUTER_JOIN(jointype) \	(((1 << (jointype)) & \	  ((1 << JOIN_LEFT) | \	   (1 << JOIN_FULL) | \	   (1 << JOIN_RIGHT) | \	   (1 << JOIN_ANTI))) != 0)

• 怎样判断jointype是否是等于1，2，3，4中的之一呢？
  • 分别是2，4，8，32，先求|,得一结果
  • 也就是(1 << (jointype)和上面结果相&
  • 如果不为零，那么说明jointype必然是等于1，2，3，4中之一

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