Question

对于我们的代码之一，雪花中的左联接行为不正确。如果您可以找到相同的解决方案，请寻求帮助。

我们有一个基本数据表连接的样本数据设置，如下所述。

CREATE TABLE patient_test(pid INT);
INSERT INTO patient_test (pid) VALUES (100);

CREATE TABLE pateint_entry_test (pid INT,DateAdded DATETIME);
INSERT INTO pateint_entry_test (pid, DateAdded) VALUES (100, '2020-07-13');

现在看下面的代码，在这里我只是为您提供我们与其他查询集一起使用的示例子查询。我们的动机是根据给定的开始/结束日期为每个患者输入日期。


WITh patient_cte  AS(
          SELECT * FROM patient_test
      )
      ,
      dates AS(
       SELECT  DATEDIFF(day, CONVERT_TIMEZONE('EST', 'UTC', CAST(TO_TIMESTAMP('2020-07-06') AS TIMESTAMP_NTZ)),
                            CONVERT_TIMEZONE('EST', 'UTC', CAST(TO_TIMESTAMP('2020-07-12') AS TIMESTAMP_NTZ))) AS Total_Days,
                            CONVERT_TIMEZONE('EST', 'UTC', CAST(TO_TIMESTAMP('2020-07-06') AS TIMESTAMP_NTZ)) AS Start_Date,
                            CONVERT_TIMEZONE('EST', 'UTC', CAST(TO_TIMESTAMP('2020-07-12') AS TIMESTAMP_NTZ)) AS end_date
      )
      ,
      cte2 (date) as (
      SELECT TO_DATE(START_DATE) FROM dates
      UNION ALL
      SELECT TO_DATE(DATEADD(day, 1, date)) FROM cte2 WHERE date < (SELECT TOP 1 END_DATE FROM dates)
      ),
      cte3 AS (
          select * from patient_cte
              cross join cte2
      )

      SELECT cte3.pid as p_pid,
        pateint_entry_test.pid as p_entry_pid,
        pateint_entry_test.DateAdded,
        cte3."DATE" ,
        IFNULL( pateint_entry_test.DateAdded, cte3."DATE") AS CALCULATEDDATEMEASURED
     FROM cte3
        LEFT JOIN pateint_entry_test ON
            cte3.pid = pateint_entry_test.pid AND
            cte3."DATE" = TO_DATE(pateint_entry_test.DateAdded)

查询的输出给出如下结果。

在这里您可以看到CALCULATEDDATEMEASURED，第2到7行是2020-07-06 00:00:00。但是由于DAETADDED会为空，因此应该根据DATE列值（根据此条件IFNULL( pateint_entry_test.DateAdded, cte3."DATE")）来确定正确的日期

期待查询的以下输出

不确定什么是错误的，但其行为不符合预期。感谢您对此的帮助。谢谢。

Answer 1

我不确定这是否是错误，但这是由于基于您编写查询的方式而强制输入的。这是在查询中使用的IFNULL语句中的TO_DATE逻辑与联接中的查询相同（并带有COALESCE以显示它产生的结果与IFNULL相同）：

WITh patient_cte  AS(
          SELECT * FROM patient_test
      )
      ,
      dates AS(
       SELECT  DATEDIFF(day, CONVERT_TIMEZONE('EST', 'UTC', CAST(TO_TIMESTAMP('2020-07-06') AS TIMESTAMP_NTZ)),
                            CONVERT_TIMEZONE('EST', 'UTC', CAST(TO_TIMESTAMP('2020-07-12') AS TIMESTAMP_NTZ))) AS Total_Days,
                            CONVERT_TIMEZONE('EST', 'UTC', CAST(TO_TIMESTAMP('2020-07-06') AS TIMESTAMP_NTZ)) AS Start_Date,
                            CONVERT_TIMEZONE('EST', 'UTC', CAST(TO_TIMESTAMP('2020-07-12') AS TIMESTAMP_NTZ)) AS end_date
      )
      ,
      cte2 (date) as (
      SELECT TO_DATE(START_DATE) FROM dates
      UNION ALL
      SELECT TO_DATE(DATEADD(day, 1, date)) FROM cte2 WHERE date < (SELECT TOP 1 END_DATE FROM dates)
      ),
      cte3 AS (
          select * from patient_cte 
              cross join cte2 
      )
      SELECT cte3.pid as p_pid,
        pateint_entry_test.pid as p_entry_pid,
        pateint_entry_test.DateAdded,
        cte3."DATE",
        IFNULL( pateint_entry_test.DateAdded, cte3."DATE") AS ORIGINAL_ERROR,
        IFNULL( to_date(pateint_entry_test.DateAdded), cte3."DATE") AS CALCULATEDDATEMEASURED,
        coalesce(to_date(pateint_entry_test.DateAdded), cte3."DATE") as from_coalesce
     FROM cte3 
        LEFT JOIN pateint_entry_test 
            ON cte3.pid = pateint_entry_test.pid 
            AND cte3."DATE" = to_date(pateint_entry_test.DateAdded);

在Snowflake中运行此命令将产生以下结果：

Snowflake SQL查询左联接问题

1 个答案: