SQL Graph, part IV Merge DML Support (aka MATCH support for the MERGE against ...

This is the 4th blog post in the series of blogpost on the Graph features within SQL Server and Azure SQL Database .

This particular post is dedicated to the support of the MERGE DML for Graph tables in Azure SQL Database , that Microsoft has announced at the Ignite in September 2018.

I am not the very best friend of the MERGE Statement for Columnstore Indexes , as you might know :), but I am a fan of the concept of the UPSERT statement (aka MERGE for Microsoft Data Platform) and I am definitely facing those statements in production on regular basis.

Even though I honestly wish that Microsoft would invest into further development and performance improvement for this T-SQL command, and while I am not expecting this to happen any time soon I still expect to see this command being used and abused in the decades to come, which brings us to the topic of the Graph Database …

The Node Table Upsets

The support for the Merge statement against the Graph Tables is already available in SQL Server 2019 Public CTPs and Azure SQL Database, and so you should be able to try it. :)

Here are the basic tests I did for the Node Tables, once it became available, where I create a table dbo.Person:

DROP TABLE IF EXISTS dbo.Person;
CREATE TABLE dbo.Person(
PersonID BIGINT NOT NULL PRIMARY KEY CLUSTERED,
FULLNAME NVARCHAR(250) NOT NULL ) AS NODE;

,

load a couple of rows into it:

DELETE FROM dbo.Person;
INSERT INTO dbo.Person
VALUES (1,'John Doe'), (2,'Andres Martins');

,

set up a new staging table dbo.PersonStagedData which shall contain the first 2 original rows but with more detailed information on the full names of the people, plus an additional row that will contain a new entry with a PersonId of 3 (aka Graph Updatio :)):

DROP TABLE IF EXISTS dbo.PersonStagedData;
CREATE TABLE dbo.PersonStagedData(
PersonID BIGINT NOT NULL PRIMARY KEY CLUSTERED,
FULLNAME NVARCHAR(250) NOT NULL );
INSERT INTO dbo.PersonStagedData
VALUES (1,'John Brian Doe'), (2,'Andres Ignacio Martins'), (3,'Grapho Updatio');

Now we are ready to UPSERT the original dbo.Person table with the information from the dbo.PersonStagedData table:

SELECT [PersonID], [FULLNAME]
FROM dbo.Person;
MERGE dbo.Person AS Target
USING (SELECT [PersonID], [FULLNAME]
FROM [dbo].[PersonStagedData])
AS Source
ON (Target.[PersonID] = Source.[PersonID])
WHEN MATCHED THEN
UPDATE SET [FULLNAME] = Source.[FULLNAME]
WHEN NOT MATCHED THEN
INSERT ([PersonID], [FULLNAME])
VALUES (Source.[PersonID], Source.[FULLNAME]) ;
SELECT [PersonID], [FULLNAME]
FROM dbo.Person;

The above presented code will executes without any warning or errors, presenting the original plus the updated results, as you can see on the image on the left of this text.

The execution plan for the MERGE DML statement is presented below

,

and you might wonder, why would the same operation would not work in the original SQL Server supporting Graph the SQL Server 2017. For this purpose I ran the very same workload against the SQL Server 2017 …

and VOIL! it worked perfectly fine! :)

because the Node Tables Upserts are perfectly functioning and are supported since the original release of the Graph Database in SQL Server.

You might have noticed that we do not have the MATCH clause in our MERGE statement, but let me assure you that even a statement like the following one will work very fine on both SQL Server 2017 and SQL Server 2019 CTP 2.2 versions:

-- The Setup part for the Node dbo.Company and the Edge dbo.Follows tables:
DROP TABLE IF EXISTS dbo.Follows;
DROP TABLE IF EXISTS dbo.Company;
CREATE TABLE dbo.Company(
CompanyID BIGINT NOT NULL PRIMARY KEY CLUSTERED,
CompanyName NVARCHAR(250) NOT NULL UNIQUE ) AS NODE;
CREATE TABLE dbo.Follows(
Since DATETIME2 NULL,
--CONSTRAINT EDG_Person_Follows CONNECTION (Person TO Company, PersonStagedData TO Company)
)
AS EDGE;
INSERT INTO dbo.Company
VALUES (1,'Creative Value Company'), (2,'Real Stuff');
INSERT INTO dbo.Follows
SELECT p1.$node_id as from_obj_id,
(SELECT p2.$node_id as to_obj_id FROM dbo.Company p2 WHERE p2.CompanyName = 'Real Stuff'),
'2019-01-01'
FROM dbo.Person p1
-- ********************************************************************************
-- The Merge Statement itself
MERGE dbo.Person AS Target
USING (SELECT PersonStagedData.PersonID, PersonStagedData.FullName
FROM PersonStagedData, Follows, Company
WHERE MATCH(PersonStagedData-(Follows)->Company)
AND CompanyName = 'Real Stuff')
AS Source
ON (Target.[PersonID] = Source.[PersonID])
WHEN MATCHED THEN
UPDATE SET [FULLNAME] = Source.[FULLNAME]
WHEN NOT MATCHED THEN
INSERT ([PersonID], [FULLNAME])
VALUES (Source.[PersonID], Source.[FULLNAME]) ;

Yeah, that worked well on my SQL Server 2017 …

Then what is really new for the SQL Server 2019 CTPs then, you might ask and the answer is simple as it is exotic: the support for the MATCH clause for the Edge Tables while using the MERGE statement:

The Edge Table Upserts (aka That Actually Added Feature)

Let us reset everything by recreating the tables and adding the dbo.Follows Edge Table between the 2 Node tables dbo.Person and dbo.Company, the same way as in the previous blog post:

DROP TABLE IF EXISTS dbo.Follows;
DROP TABLE IF EXISTS dbo.Person;
DROP TABLE IF EXISTS dbo.Company;
CREATE TABLE dbo.Person(
PersonID BIGINT NOT NULL PRIMARY KEY CLUSTERED,
FULLNAME NVARCHAR(250) NOT NULL ) AS NODE;
CREATE TABLE dbo.Company(
CompanyID BIGINT NOT NULL PRIMARY KEY CLUSTERED,
CompanyName NVARCHAR(250) NOT NULL UNIQUE ) AS NODE;
CREATE TABLE dbo.Follows(
Since DATETIME2 NULL,
CONSTRAINT EDG_Person_Follows CONNECTION (Person TO Company, PersonStagedData TO Company)
)
AS EDGE;

Let’s insert the data that every person will like every company (2 people and 2 companies), starting with the date of the 1st of January of 2019:

TRUNCATE TABLE dbo.Follows;
DELETE FROM dbo.Person;
DELETE FROM dbo.Company;
INSERT INTO dbo.Person
VALUES (1,'John Doe'), (2,'Andres Martins');
INSERT INTO dbo.Company
VALUES (1,'Creative Value Company'), (2,'Real Stuff');
INSERT INTO dbo.Follows
SELECT p1.$node_id as from_obj_id,
(SELECT p2.$node_id as to_obj_id FROM dbo.Company p2 WHERE p2.CompanyName = 'Real Stuff'),
'2019-01-01'
FROM dbo.Person p1
INSERT INTO dbo.Follows
SELECT p1.$node_id as from_obj_id,
(SELECT p2.$node_id as to_obj_id FROM dbo.Company p2 WHERE p2.CompanyName NOT like 'Real%' ),
'2019-01-01'
FROM dbo.Person p1

Now let’s upsert the data for the Edges of the ‘Real Stuff’ company with the value of the 1st of January of 2001

SELECT Person.FullName, Follows.Since as FollowsSince, Company.CompanyName
FROM dbo.Follows, dbo.Person, dbo.Company
WHERE MATCH(Person-(Follows)->Company)
MERGE dbo.Follows
USING (SELECT PersonID, FullName
FROM Person)
AS Source
INNER JOIN dbo.Company
ON Company.