Add auto increment with labeled primary key to existing table in SQL Server and H2 / Liquibase - sql

Question

I am currently using liquibase to apply changes to H2 and SQL Server.
Goal:
add a column id with auto increment to an existing table
add a primary key constraint with constraint name to id
Liquibase auto increment does not support SQL Server so I need to find a solution in SQL.
What I want is something like this:
<sql>
ALTER TABLE user ADD COLUMN id INT NOT NULL AUTO_INCREMENT;
</sql>
<addPrimaryKey columnNames="id" constraintName="userPK" tableName="user"/>
This statement is only working in H2 but not in SQL Server.
For SQL Server, IDENTITY seems to be the command to apply auto increment so I tried to write another statement that uses IDENTITY instead.
The problem with IDENTITY is that it automatically creates a primary key when using H2 which is not what I want because I would have to somehow find and rename it. SQL Server does not automatically create this primary key when using IDENTITY.
It is important to control the name of the primary key and that the name is the same for both databases.
I would appreciate any help.
Edit:
Another attempt was to split the sql commands:
<sql dbms="h2">
ALTER TABLE user ADD ID INT auto_increment;
</sql>
<sql dbms="mssql">
ALTER TABLE user ADD id INT IDENTITY(1, 1);
</sql>
<addPrimaryKey columnNames="id" constraintName="userPK" tableName="user"/>
H2 however ignores the constraintName in addPrimaryKey and instead generates another name. I wanted the names to be the same but I noticed that I can still use dropPrimaryKey to drop it.

Answer 1

Unfortunately, H2 1.4.200 doesn't yet emulate non-standard IDENTITY clause from SQL Server well enough and SQL Server doesn't support standard identity columns (ID BIGINT GENERATED BY DEFAULT AS IDENTITY etc.) supported by H2 and various other DBMS.
You need to compile H2 from its current sources available on GitHub:
https://github.com/h2database/h2database
There are build.cmd and build.sh scripts in h2 subdirectory. You need to launch a proper script for you OS with jar argument (build jar or ./build.sh jar). Use Java 8 or 11 (compiled jar will be compatible with more recent versions too).
With the compiled snapshot version you will be able to use
CREATE TABLE TEST1(ID BIGINT IDENTITY, V INT);
CREATE TABLE TEST2(V INT);
ALTER TABLE TEST2 ADD ID BIGINT IDENTITY;
and similar commands in MSSQLServer compatibility mode (append ;MODE=MSSQLServer to JDBC URL) and these commands will not create unexpected primary key constraints.