create unique index with function in hsqldb / liquibase - postgresql

Question

Is there a way to use function index in hsqldb?
I tried those 4:
<column name="LOWER(name)"/>
<column name="LCASE(name)"/>
<column name="LOWER(name)" computed="true"/>
<column name="LCASE(name)" computed="true"/>
Inside my createIndex changeset:
<changeSet author="dgt" id="unique-postgres" dbms="hsqldb">
<createIndex indexName="lower_case_index" tableName="users" unique="true">
<column name="LOWER(name)" computed="true"/>
</createIndex>
In documentation I noticed that hsqldb got: LOWER and LCASE built in function, but any of those do not work for me.
Every single time I've got an error:
Reason: liquibase.exception.DatabaseException: unexpected token: (
required: ) [Failed SQL: CREATE UNIQUE INDEX PUBLIC.lower_case_index
ON PUBLIC.users(LOWER(name))]
I know about a solution that I can change column type from VARCHAR to VARCHAR_IGNORECASE, but it's not a case for me, because I need a solution to work on both db: hsqldb and postgres.
My ideal solution should look like this:
<changeSet author="dgt" id="users-unique-index-postgres" dbms="hsqldb">
<createIndex indexName="name_index" tableName="users" unique="true">
<column name="LOWER(name)" computed="true"/>
</createIndex>
</changeSet>
<changeSet author="dgt" id="users-unique-index-hsqldb" dbms="postgresql">
<createIndex indexName="name_index" tableName="users" unique="true">
<column name="lower(name)" computed="true"/>
</createIndex>
</changeSet>
But it doesn't work.

Answer 1

HSQLDB does not support function based indexes at all, so you need to find a different solution. You could e.g. define the column as varchar_ignorecase instead of varchar and then create a "normal" unique index on that column.
You can keep a single table definition by using properties.
That could look like this:
<changeSet author="dgt" id="create-users-table">
<property name="users_name_type" value="varchar" dbms="postgresql"/>
<property name="users_name_type" value="varchar_ignorecase" dbms="hsqldb"/>
<createTable tableName="users">
<column name="name" type="${users_name_type}">
<constraints nullable="false"/>
</column>
</createTable>
</changeSet>
<changeSet author="dgt" id="users-unique-index-postgres" dbms="postgresql">
<createIndex indexName="name_index" tableName="users" unique="true">
<column name="lower(name)" computed="true"/>
</createIndex>
</changeSet>
<changeSet author="dgt" id="users-unique-index-hsqldb" dbms="hsqldb">
<createIndex indexName="name_index" tableName="users" unique="true">
<column name="name"/>
</createIndex>
</changeSet>