【转】left join的总结

EG1:通俗的讲 A left join B 的连接的记录数与A表的记录数同 A right join B 的连接的记录数与B表的记录数同 A left join B 等价B right join A table A: Field_K, Field_A 1 a 3 b 4 c table B: Field_K, Field_B 1 x 2 y 4 z select a.Field_K, a.Field_A, b.Field_K, b.Field_B from a left join b on a.Field_K=b.Field_K Field_K Field_A Field_K Field_B ---------- ---------- ---------- ---------- 1 a 1 x 3 b NU