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Update

Translation reference to convert SQL Server Update statement to Snowflake

Some parts in the output code are omitted for clarity reasons.

Description

Changes existing data in a table or view in SQL Server. For more information regarding SQL Server Update, check here.

[ WITH <common_table_expression> [...n] ]  
UPDATE   
    [ TOP ( expression ) [ PERCENT ] ]   
    { { table_alias | <object> | rowset_function_limited   
         [ WITH ( <Table_Hint_Limited> [ ...n ] ) ]  
      }  
      | @table_variable      
    }  
    SET  
        { column_name = { expression | DEFAULT | NULL }  
          | { udt_column_name.{ { property_name = expression  
                                | field_name = expression }  
                                | method_name ( argument [ ,...n ] )  
                              }  
          }  
          | column_name { .WRITE ( expression , @Offset , @Length ) }  
          | @variable = expression  
          | @variable = column = expression  
          | column_name { += | -= | *= | /= | %= | &= | ^= | |= } expression  
          | @variable { += | -= | *= | /= | %= | &= | ^= | |= } expression  
          | @variable = column { += | -= | *= | /= | %= | &= | ^= | |= } expression  
        } [ ,...n ]   
  
    [ <OUTPUT Clause> ]  
    [ FROM{ <table_source> } [ ,...n ] ]   
    [ WHERE { <search_condition>   
            | { [ CURRENT OF   
                  { { [ GLOBAL ] cursor_name }   
                      | cursor_variable_name   
                  }   
                ]  
              }  
            }   
    ]   
    [ OPTION ( <query_hint> [ ,...n ] ) ]  
[ ; ]  
  
<object> ::=  
{   
    [ server_name . database_name . schema_name .   
    | database_name .[ schema_name ] .   
    | schema_name .  
    ]  
    table_or_view_name}

Sample Source Patterns

Basic UPDATE

The conversion for a regular UPDATE statement is very straightforward. Since the basic UPDATE structure is supported by default in Snowflake, the outliers are the parts where you are going to see some differences, check them in the Known Issues section.

SQL Server

IN -> SqlServer_01.sql
Update UpdateTest1
Set Col1 = 5;

Snowflake

OUT -> SqlServer_01.sql
Update UpdateTest1
Set
Col1 = 5;

UPDATE with FROM clause and JOIN

In cases where the UPDATE statement has a FROM clause that contains JOINs, however, there are some changes done, since Snowflake does not allow the usage of JOINs with the table being updated. These changes are as follows:

  • All the joined elements (either tables or subqueries) are moved to the list of FROM elements

  • All the expressions that come inside the ON clauses after each JOIN are moved to a WHERE clause, joined by AND. If a WHERE clause already exists in the statement, the original expressions of the WHERE clause are preserved at the end of that WHERE clause, while the expressions moved from the ON clause is added at the beginning.

  • Depending on if the JOIN was LEFT JOIN or RIGHT JOIN, the expression to the left or right of the conditional operation will include as a way to replicate the functionality of the original JOIN.

    • LEFT JOIN: The right side of the conditional is modified.

    • RIGHT JOIN: The left side of the conditional is modified

SQL Server

IN -> SqlServer_02.sql
UPDATE
  test_sales.commissions
SET
  test_sales.commissions.commission = 5
FROM
  test_sales.commissions c
LEFT JOIN
  test_sales.targets t
ON
  c.target_id = t.target_id
RIGHT JOIN
	(SELECT * FROM ATABLE) a
ON
	c.target_id = a.target_id;

Snowflake

OUT -> SqlServer_02.sql
UPDATE test_sales.commissions c
	SET
		test_sales.commissions.commission = 5
	FROM
		test_sales.targets t,
		(SELECT
				*
			FROM
				ATABLE
		) a
	WHERE
		test_sales.commissions.target_id = t.target_id(+)
		AND test_sales.commissions.target_id(+) = a.target_id;

Cartesian Products

SQL Server allows add circular references between the target table of the Update Statement and the FROM Clause/ In execution time, the database optimizer removes any cartesian product generated. Otherwise, Snowflake currently does not optimize this scenario, producing a cartesian product that can be checked in the Execution Plan.\

To resolve this, if there is a JOIN where one of their tables is the same as the update target, this reference is removed and added to the WHERE clause, and it is used to just filter the data and avoid making a set operation.

SQL Server

IN -> SqlServer_03.sql
UPDATE [HumanResources].[EMPLOYEEDEPARTMENTHISTORY_COPY]
SET
	BusinessEntityID = b.BusinessEntityID ,
	DepartmentID = b.DepartmentID,
	ShiftID = b.ShiftID,
	StartDate = b.StartDate,
	EndDate = b.EndDate,
	ModifiedDate = b.ModifiedDate
	FROM [HumanResources].[EMPLOYEEDEPARTMENTHISTORY_COPY] AS a
	RIGHT OUTER JOIN [HumanResources].[EmployeeDepartmentHistory] AS b
	ON a.BusinessEntityID = b.BusinessEntityID and a.ShiftID = b.ShiftID;

Snowflake

OUT -> SqlServer_03.sql
UPDATE HumanResources.EMPLOYEEDEPARTMENTHISTORY_COPY a
	SET
		BusinessEntityID = b.BusinessEntityID,
		DepartmentID = b.DepartmentID,
		ShiftID = b.ShiftID,
		StartDate = b.StartDate,
		EndDate = b.EndDate,
		ModifiedDate = b.ModifiedDate
	FROM
		HumanResources.EmployeeDepartmentHistory AS b
	WHERE
		HumanResources.EMPLOYEEDEPARTMENTHISTORY_COPY.BusinessEntityID = b.BusinessEntityID(+)
		AND HumanResources.EMPLOYEEDEPARTMENTHISTORY_COPY.ShiftID = b.ShiftID;

Known Issues

OUTPUT clause

The OUTPUT clause is not supported by Snowflake.

SQL Server

IN -> SqlServer_04.sql
Update UpdateTest2
Set Col1 = 5
OUTPUT
	deleted.Col1,
	inserted.Col1
	into ValuesTest;

Snowflake

OUT -> SqlServer_04.sql
Update UpdateTest2
	Set
		Col1 = 5
----** SSC-FDM-0028 - OUTPUT CLAUSE NOT SUPPORTED IN SNOWFLAKE **
--OUTPUT
--	deleted.Col1,
--	inserted.Col1
--	into ValuesTest
	               ;

CTE

The WITH CTE clause is moved to the internal query in the update statement to be supported by Snowflake.

SQL Server

IN -> SqlServer_05.sql
With ut as (select * from UpdateTest3)
Update x
Set Col1 = 5 
from ut as x;

Snowflake

OUT -> SqlServer_05.sql
UPDATE UpdateTest3
Set
Col1 = 5
FROM
(
WITH ut as (select
*
from
UpdateTest3
)
SELECT
*
FROM
ut
) AS x;

TOP clause

The TOP clause is not supported by Snowflake.

SQL Server

IN -> SqlServer_06.sql
Update TOP(10) UpdateTest4
Set Col1 = 5;

Snowflake

OUT -> SqlServer_06.sql
Update
--       --** SSC-FDM-0028 - TOP CLAUSE NOT SUPPORTED IN SNOWFLAKE **
--       TOP(10)
               UpdateTest4
Set
Col1 = 5;

WITH TABLE HINT LIMITED

The Update WITH clause in not supported by Snowflake.

SQL Server

IN -> SqlServer_07.sql
Update UpdateTest5 WITH(TABLOCK)
Set Col1 = 5;

Snowflake

OUT -> SqlServer_07.sql
Update UpdateTest5
Set
Col1 = 5;

Related EWIs

  1. SSC-FDM-0028: Not supported.

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