union/union all

用于合并两个或多个 select / exec 查询的结果集。union 会将重复的记录删去，union all 保留所有记录。支持在分布式查询中使用。

注意：

  • union / union all 连接的 select / exec 语句必须查询相同数量的列，且对应列的类型必须能够相互转换；

  • 第一个查询的列名和类型决定了结果集的列名和列类型。

例子

t1= table(1 2 3 3 as id, 7.8 4.6 5.1 0.1 as v1)
t2 = table(5 3 3 as id,  3.2 5.1 0.1 as v2);
select * from t1 union select * from t2
id v1
1 7.8
2 4.6
3 5.1
3 0.1
5 3.2 
select * from t1 union all select * from t2
id v1
1 7.8
2 4.6
3 5.1
3 0.1
5 3.2
3 5.1
3 0.1 
t3 = table(3 3 4 as id,  5.1 0.2 1.1 as v3);
(select * from t1 where id=3) union all (select * from t2 where id=3) union (select * from t3 where id=3)
id v1
3 5.1
3 0.1
3 0.2