[ 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
SQL Server:
IN -> SqlServer_01.sql
WITH ctetable(col1, col2) AS
(
SELECT col1, col2 FROM t1 poh WHERE poh.col1 = 16 and 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 = 16 and 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,d
FROM CTE
WHERE e IS NOT NULL;
Snowflake:
OUT -> SqlServer_02.sql
INSERT INTO Table2 (a, b, c, d)
WITH CTE AS( SELECT
*
from
table1
)
SELECT
a,
b,
c,
d
FROM
CTE AS CTE
WHERE
e 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 RN
FROM WithQueryTest
)
DELETE FROM Duplicated
WHERE 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.WithQueryTest
QUALIFY 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
SQL Server:
IN -> SqlServer_03.sql
WITH ctetable(col1, col2) as
(
SELECT col1, col2
FROM t1 poh
where poh.col1 = 16 and poh.col2 = 88
),
finalCte As
(
SELECT col1 FROM ctetable
)
MERGE
table1 AS target
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 AS target
USING (
--** SSC-PRF-TS0001 - PERFORMANCE WARNING - RECURSION FOR CTE NOT CHECKED. MIGHT REQUIRE RECURSIVE KEYWORD **
WITH ctetable (
col1,
col2
) as
(
SELECT
col1,
col2
FROM
t1 poh
where
poh.col1 = 16 and poh.col2 = 88
),
finalCte As
(
SELECT
col1
FROM
ctetable
)
SELECT
*
FROM
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);
Common Table Expression with UPDATE statement
SQL Server:
IN -> SqlServer_04.sql
WITH ctetable(col1, col2) AS
(
SELECT col1, col2
FROM table2 poh
WHERE poh.col1 = 5 and poh.col2 = 4
)
UPDATE tab1
SET ID = 8, COL1 = 8
FROM table1 tab1
INNER 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 = 5 and poh.col2 = 4
)
SELECT
*
FROM
ctetable
) AS CTE
WHERE
tab1.ID = CTE.col1;
