Pengcheng Xiong created HIVE-9008:
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Summary: primary table in union
Key: HIVE-9008
URL: https://issues.apache.org/jira/browse/HIVE-9008
Project: Hive
Issue Type: Sub-task
Reporter: Pengcheng Xiong
Following http://dev.mysql.com/doc/refman/5.0/en/union.html
The column names from the first SELECT statement are used as the column names
for the results returned. Selected columns listed in corresponding positions of
each SELECT statement should have the same data type. (For example, the first
column selected by the first statement should have the same type as the first
column selected by the other statements.)
If the data types of corresponding SELECT columns do not match, the types and
lengths of the columns in the UNION result take into account the values
retrieved by all of the SELECT statements.
We can say
select A.id from A
union
select B.id from B
order by id
We can say
select A.id as a from A
union
select B.id from B
order by a
We can NOT say
select A.id as a from A
union
select B.id from B
order by A.id
ERROR 1054 (42S22): Unknown column 'A.id' in 'order clause'
We can NOT say
select A.id as a from A
union
select B.id from B
order by B.id
ERROR 1054 (42S22): Unknown column 'B.id' in 'order clause'
We can say
select A.id as a from A
union
(select B.id from B
order by B.id)
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