Snowflake没有实现完整的SQL MERGE语句？

Question

我正在尝试创建一个执行 MERGE 语句的 Snowflake 任务。

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但是，Snowflake 似乎无法识别 \xe2\x80\x9c（当与 target\xe2\x80\x9d 不匹配时）或 \xe2\x80\x9c（当与 source\xe2\x80\x9d 语句不匹配时）。

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create or replace task MERGE_TEAM_TOUCHPOINT\n warehouse = COMPUTE_WH\n schedule = '1 minute'\n when system$stream_has_data('TEAMTOUCHPOINT_CDC')\nas\nmerge into dv.Team_Touchpoint as f using TeamTouchpoint_CDC as s\n    on s.uniqueid = f.uniqueid\n    when matched then \n        update set TEAMUNIQUEID = s.TEAMUNIQUEID,\n                    TOUCHPOINTUNIQUEID = s.TOUCHPOINTUNIQUEID\n    when not matched by target then \n                   insert (\n                     ID,\n                     UniqueID,\n                     TEAMUNIQUEID,\n                     TOUCHPOINTUNIQUEID                   \n                   )\n                 values (\n                    s.ID,\n                    s.UniqueID,\n                    s.TEAMUNIQUEID,\n                    s.TOUCHPOINTUNIQUEID\n                 )\n    when not matched by source then delete;\n

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我怎样才能做到这一点？除了在 JavaScript 中创建一个存储过程来首先截断表，然后插入临时表中的所有内容之外，真的没有其他方法吗？

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Answer 1

队友建议的解决方法：

• MATCHED_BY_SOURCE基于全连接定义，然后查看a.col或b.col是否为null：

merge into TARGET t
using (
    select <COLUMN_LIST>,
    iff(a.COL is null, 'NOT_MATCHED_BY_SOURCE', 'MATCHED_BY_SOURCE') SOURCE_MATCH,
    iff(b.COL is null, 'NOT_MATCHED_BY_TARGET', 'MATCHED_BY_TARGET') TARGET_MATCH
    from SOURCE a
    full join TARGET b
    on a.COL = b.COL
) s
on s.COL = t.COL
when matched and s.SOURCE_MATCH = 'NOT_MATCHED_BY_SOURCE' then
<DO_SOMETHING>
when matched and s.TARGET_MATCH = 'NOT_MATCHED_BY_TARGET' then
<DO_SOMETHING_ELSE>
;

（与/sf/answers/4836665781/相同）

Answer 2

“按目标”和“按源”都不是 Snowflake 的 MERGE 命令中的有效关键字，并且匹配仅是“按目标”( https://docs.snowflake.com/en/sql-reference/sql/合并.html）。为了实现您的目标，您需要与合并分开运行删除 - 在合并中您将能够运行更新（当匹配时）和插入（当“按目标”不匹配时），因为实际上可以处理删除仅当“按目标”匹配时才进行合并。

您可以在存储过程中的单个显式事务中处理两个步骤（1.DELETE；2.MERGE-UPDATE&INSERT），或者通过两个单独的任务（其中之一是 AFTER 任务）处理两个不同的事务。

或者，您可以使用可选参数OVERWRITE运行 INSERT ，这将运行目标表的 TRUNCATE 并随后从源表加载，所有这些都在单个事务中进行： https ://docs.snowflake.com/en/sql-参考/sql/insert.html#可选参数

以下是 DELETE + MERGE(UPDATE&INSERT) 方法的可重现示例：

USE DEV;

CREATE OR REPLACE TEMPORARY TABLE Public.My_Merge_Target (
    Id INTEGER, Name VARCHAR    
)
AS
SELECT column1, column2 
FROM (VALUES (1, 'Stay as is'), (2, 'This name has to change'), (3, 'This needs to go'));

CREATE OR REPLACE TEMPORARY TABLE Public.My_Merge_Source (
    Id INTEGER, Name VARCHAR  
)
AS
SELECT column1, column2 
FROM (VALUES (1, 'Stay as is'), (2, 'This is the new name for id=2'), (4, 'A new row'));



SELECT * FROM Public.My_Merge_Target ORDER BY Id;
/*  
------------------------------------
    Id  | Name
------------------------------------
    1   | Stay as is
    2   | This name has to change
    3   | This needs to go    
*/


SELECT * FROM Public.My_Merge_Source ORDER BY Id;
/*
------------------------------------
    Id  | Name
------------------------------------
    1   | Stay as is
    2   | This is the new name for id=2
    4   | A new row
*/


DELETE FROM Public.My_Merge_Target AS trg
USING (
  SELECT t.Id FROM Public.My_Merge_Source AS s
  RIGHT JOIN Public.My_Merge_Target AS t 
    ON s.Id = t.Id
  WHERE s.Id IS NULL
) AS src
WHERE trg.Id = src.Id;

/*
-----------------------
number of rows deleted 
-----------------------
                     1 
-----------------------                      
*/

SELECT * FROM Public.My_Merge_Target ORDER BY Id;
/*  
------------------------------------
    Id  | Name
------------------------------------
    1   | Stay as is
    2   | This is the new name
*/

MERGE 
    INTO Public.My_Merge_Target AS trg
USING (
    SELECT Id, Name 
    FROM Public.My_Merge_Source
) AS src
ON 
    trg.Id = src.Id
WHEN
    MATCHED 
    AND (src.Name != trg.Name) THEN UPDATE 
        SET Name = src.Name
WHEN 
    NOT MATCHED THEN INSERT (Id, Name) 
        VALUES (src.Id, src.Name)
;    
/*
-------------------------------------------------
number of rows inserted | number of rows updated
-------------------------------------------------
                      1 |                      1
-------------------------------------------------                      
*/

SELECT * FROM Public.My_Merge_Target ORDER BY Id;
/*  
------------------------------------
    Id  | Name
------------------------------------
    1   | Stay as is
    2   | This is the new name for id=2
    4   | A new row
*/