如何为Amazon redshift数据库编写查询，以便相关查询的where子句有两个条件？

Question

示例 -

SELECT date, name, 
       (SELECT value
        FROM this_table
        WHERE col1= 'test1' and col2='test'
       ) AS num_sloths_bought_before
FROM source_table;

当我在redshift中执行查询时，我收到此错误 -

[Amazon](500310) Invalid operation: This type of correlated subquery pattern is not supported yet;

Answer 1

您通常可以使用连接重写相关标量子查询，对于您的查询，它是左连接：

SELECT date, name, dt.value AS num_sloths_bought_before
FROM source_table
LEFT JOIN
 ( SELECT val, 
      value
   FROM this_table
   WHERE col2='test'
 ) this_table
ON source_table.val= this_table.val;