[ WITH [ RECURSIVE ]<cte_name1> ( <cte_column_list> ) AS ( anchorClause UNION ALL recursiveClause ) [ , <cte_name2> ( <cte_column_list> ) AS ( anchorClause UNION ALL recursiveClause ) ] [ , <cte_nameN> ( <cte_column_list> ) AS ( anchorClause UNION ALL recursiveClause ) ]]SELECT ...
Where:
anchorClause ::= SELECT <anchor_column_list> FROM ...recursiveClause ::= SELECT <recursive_column_list> FROM ... [ JOIN ... ]
Noteworthy details
The RECURSIVE keyword does not exist in T-SQL, and the transformation does not actively add the keyword to the result. A warning is added to the output code in order to state this behavior.
Common Table Expression with SELECT INTO
The following transformation occurs when the WITH expression is followed by an SELECT INTO statement and it will be transformed into a TEMPORARY TABLE.
SQL Server:
IN -> SqlServer_01.sql
WITH ctetable(col1, col2) AS ( SELECT col1, col2 FROM t1 poh WHERE poh.col1 =16and poh.col2 =4 ), employeeCte AS ( SELECT BUSINESSENTITYID, VACATIONHOURS FROM employee WHERE BUSINESSENTITYID = (SELECT col1 FROM ctetable) ), finalCte AS ( SELECT BUSINESSENTITYID, VACATIONHOURS FROM employeeCte ) SELECT * INTO #table2 FROM finalCte;SELECT * FROM #table2;
Snowflake:
OUT -> SqlServer_01.sql
CREATE OR REPLACE TEMPORARY TABLE T_table2 AS WITH ctetable ( col1, col2 ) AS ( SELECT col1, col2 FROM t1 poh WHERE poh.col1 =16and poh.col2 =4 ), employeeCte AS ( SELECT BUSINESSENTITYID, VACATIONHOURS FROM employee WHERE BUSINESSENTITYID = (SELECT col1 FROM ctetable ) ), finalCte AS ( SELECT BUSINESSENTITYID, VACATIONHOURS FROM employeeCte ) SELECT* FROM finalCte; SELECT* FROM T_table2;
Common Table Expression with other expressions
The following transformation occurs when the WITH expression is followed by INSERT or DELETE statements.
SQL Server:
IN -> SqlServer_02.sql
WITH CTE AS( SELECT *from table1)INSERT INTO Table2 (a,b,c,d)SELECT a,b,c,dFROM CTEWHERE e IS NOT NULL;
Snowflake:
OUT -> SqlServer_02.sql
INSERT INTO Table2 (a, b, c, d)WITH CTE AS( SELECT*fromtable1)SELECTa,b,c,dFROMCTE AS CTEWHEREe IS NOT NULL;
Common Table Expression with Delete From
For this transformation, it will only apply for a CTE (Common Table Expression) with a Delete From, however, only for some specifics CTE. It must have only one CTE, and it must have inside a function of ROW_NUMBER or RANK.
The purpose of the CTE with the Delete must be to remove duplicates from a table. In case that the CTE with Delete intents to remove another kind of data, this transformation will not apply.
Let's see an example. For a working example, we must first create a table with some data.
CREATE TABLE WithQueryTest( ID BIGINT,Value BIGINT, StringValue NVARCHAR(258));Insert into WithQueryTest values(100, 100, 'First');Insert into WithQueryTest values(200, 200, 'Second');Insert into WithQueryTest values(300, 300, 'Third');Insert into WithQueryTest values(400, 400, 'Fourth');Insert into WithQueryTest values(100, 100, 'First');
Note that there is a duplicated value. The lines 8 and 12 insert the same value. Now we are going to eliminate the duplicates rows in a table.
WITH Duplicated AS (SELECT *, ROW_NUMBER() OVER (PARTITION BY ID ORDER BY ID) AS RNFROM WithQueryTest)DELETE FROM DuplicatedWHERE Duplicated.RN >1
If we execute a Select from the table, it will show the following result
Note that there are no duplicateds rows. In order to conserve the functionality of these CTE with Delete in Snowflake, it will be transformed to
CREATE OR REPLACE TABLE PUBLIC.WithQueryTest AS SELECT*FROM PUBLIC.WithQueryTestQUALIFY ROW_NUMBER()OVER (PARTITION BY ID ORDER BY ID) =1 ;
As you can see, the query is transformed to a Create Or Replace Table.
Let's try it in Snowflake, in order to test it, we need the table too.
CREATE OR REPLACE TABLE PUBLIC.WithQueryTest(ID BIGINT,Value BIGINT,StringValue VARCHAR(258));Insert into PUBLIC.WithQueryTest values(100, 100, 'First');Insert into PUBLIC.WithQueryTest values(200, 200, 'Second');Insert into PUBLIC.WithQueryTest values(300, 300, 'Third');Insert into PUBLIC.WithQueryTest values(400, 400, 'Fourth');Insert into PUBLIC.WithQueryTest values(100, 100, 'First');
Now, if we execute the result of the transformation, and then a Select to check if the duplicated rows were deleted, this would be the result.
Common Table Expression with MERGE statement
The following transformation occurs when the WITH expression is followed by MERGE statement and it will be transformed into a MERGE INTO.
SQL Server:
IN -> SqlServer_03.sql
WITH ctetable(col1, col2) as ( SELECT col1, col2 FROM t1 pohwhere poh.col1 =16and poh.col2 =88 ), finalCte As ( SELECT col1 FROM ctetable ) MERGE table1 AStarget USING finalCte AS source ON (target.ID = source.COL1) WHEN MATCHED THEN UPDATE SET target.ID = source.Col1 WHEN NOT MATCHED THEN INSERT (ID, col1) VALUES (source.COL1, source.COL1 );
Snowflake:
OUT -> SqlServer_03.sql
MERGE INTO table1 AStargetUSING (--** SSC-PRF-TS0001 - PERFORMANCE WARNING - RECURSION FOR CTE NOT CHECKED. MIGHT REQUIRE RECURSIVE KEYWORD ** WITH ctetable ( col1, col2 ) as ( SELECT col1, col2 FROM t1 pohwhere poh.col1 =16and poh.col2 =88 ), finalCte As ( SELECT col1 FROM ctetable ) SELECT* FROM finalCte) AS sourceON (target.ID = source.COL1)WHEN MATCHED THEN UPDATE SET target.ID = source.Col1WHEN NOT MATCHED THEN INSERT (ID, col1) VALUES (source.COL1, source.COL1);
Common Table Expression with UPDATE statement
The following transformation occurs when the WITH expression is followed by an UPDATE statement and it will be transformed into an UPDATE statement.
SQL Server:
IN -> SqlServer_04.sql
WITH ctetable(col1, col2) AS ( SELECT col1, col2 FROM table2 poh WHERE poh.col1 =5and poh.col2 =4 )UPDATE tab1SET ID =8, COL1 =8FROM table1 tab1INNER JOIN ctetable CTE ON tab1.ID = CTE.col1;
Snowflake:
OUT -> SqlServer_04.sql
UPDATE dbo.table1 tab1 SET ID =8, COL1 =8 FROM ( WITH ctetable ( col1, col2 ) AS ( SELECT col1, col2 FROM table2 poh WHERE poh.col1 =5and poh.col2 =4 ) SELECT* FROM ctetable ) AS CTE WHERE tab1.ID = CTE.col1;
Known Issues
No issues were found.
Related EWIs
SSC-EWI-0108: The following subquery matches at least one of the patterns considered invalid and may produce compilation errors.
SSC-PRF-TS0001: Performance warning - recursion for CTE not checked. Might require a recursive keyword.