select - (黑斑羚)分析异常 : Subqueries are not supported in the select list

Question

我有一个这样的查询，并且 Impala 似乎不支持 SELECT 语句中的子查询。我怎样才能在 Impala 中巧妙地重写它？

SELECT
  col1,
  col2,
  ...
  CASE
    WHEN (SELECT 1
          FROM
            table1 x,
            table2 y
          WHERE
            x.id = y.id
          LIMIT 1) = 1
    THEN
      'A'
    ELSE
      'B'
  END
    coln

FROM
...

您的查询有以下错误:

AnalysisException:选择列表中不支持子查询。

Answer 1

你可以试试

SELECT col1, col2, ... 'A' coln
  FROM ...
  WHERE EXISTS (SELECT 1 FROM table1 x, table2 y WHERE x.id = y.id LIMIT 1)
UNION ALL
SELECT col1, col2, ... 'B' coln
  FROM ...
  WHERE NOT EXISTS (SELECT 1 FROM table1 x, table2 y WHERE x.id = y.id LIMIT 1)

不保证，我自己还没有尝试过。