如何在Hive SQL中实现类似OUTER UNION CORR的结果？

Question

我试图通过组合多个表来创建一个表，但我需要得到我的输出表上的所有列。

Create table output_table
Select cl1, cl2, cl3, cl4
From table1
Union all
Select cl1, cl2, cl3, cl5
From table2
Union all
Select cl1, cl2, cl3, cl6
From table3
Union all
Select cl1, cl2, cl3, cl7
From table4 

在这种情况下，我的输出表应该包含所有的列。

有没有什么方法可以得到这个，请问

Answer 1

我会在Hive中尝试这样做（我想所有的列都是字符串，如果不是的话，你可以输入另一个值，例如，如果字段是int，你可以输入0而不是''，或者你也可以输入null，最终的结果是一样的）。

CREATE TABLE output_table
ROW FORMAT DELIMITED FIELDS TERMINATED BY ','
STORED AS TEXTFILE
AS
SELECT cl1, cl2, cl3, cl4, '' AS cl5, '' AS cl6, '' AS cl7
FROM table1
UNION ALL
SELECT '' AS cl1, '' AS cl2, '' AS cl3, '' AS cl4, cl5, '' AS cl6, '' AS cl7
FROM table2
UNION ALL
SELECT '' AS cl1, '' AS cl2, '' AS cl3, '' AS cl4, '' AS cl5, cl6, '' AS cl7
FROM table3
UNION ALL
SELECT '' AS cl1, '' AS cl2, '' AS cl3, '' AS cl4, '' AS cl5, '' AS cl6, cl7
FROM table4;

然后，你可以清理这个表，如下创建另一个表作为最后一个表。

CREATE TABLE final_table
ROW FORMAT DELIMITED FIELDS TERMINATED BY ','
STORED AS TEXTFILE
AS
SELECT t.cl1, t1.cl2,t2.cl3,t3.cl4,t4.cl5,t5.cl6,t6.cl7
FROM (SELECT cl1 FROM output_table WHERE cl1 <> '') AS t,
     (SELECT cl2 FROM output_table WHERE cl2 <> '') AS t1,
     (SELECT cl3 FROM output_table WHERE cl3 <> '') AS t2,
     (SELECT cl4 FROM output_table WHERE cl4 <> '') AS t3,
     (SELECT cl5 FROM output_table WHERE cl5 <> '') AS t4,
     (SELECT cl6 FROM output_table WHERE cl6 <> '') AS t5,
     (SELECT cl7 FROM output_table WHERE cl7 <> '') AS t6;