Hive支持的表连接查询的语法：
join_table:
table_reference JOIN table_factor [join_condition]
| table_reference {LEFT|RIGHT|FULL} [OUTER] JOIN table_reference join_condition
| table_reference LEFT SEMI JOIN table_reference join_condition
| table_reference CROSS JOIN table_reference [join_condition] (as of Hive 0.10)
table_reference:
table_factor
| join_table
table_factor:
tbl_name [alias]
| table_subquery alias
| ( table_references )
join_condition:
ON equality_expression ( AND equality_expression )*
equality_expression:
expression = expression
hive只支持等连接，外连接，左半连接。hive不支持非相等的join条件（可以通过其他方式实现），因为它很难在map/reduce job实现这样的条件。而且，hive可以join两个以上的表。