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## Environment
**Liquibase Version**: 4.2.2

**Liquibase Integration & Version**: Maven

**Liquibase Extension(s) & Version**: NA

**Database Vendor & Version**: com.ibm.db2:db2jcc_license_cisuz & 9.7.5

**Operating System Type & Version**: Windows 7 Enterprise

## Description
I tried to implement Liquibase for my IBM DB2 zos database and when i run liquibase:generateChangeLog command, I’m getting the following error.

Error setting up or running Liquibase: liquibase.command.CommandExcecutionExceptoin: liquibase.exception.DatabaseException: Error executing SQL select CONSTRAINT_NAME, COLUMN_LIST as COLUMN_NAME, constraint_schema as CONSTRAINT_CONTAINER from information_schema.constraints where constraint_type=‘UNIQUE’ and …; DB2 SQL Error: SQLCODE=-204, SQLSTATE=42704, SQLERRMC=INFORMATION_SCHEMA.CONSTRAINTS, DRIVER=4.25.13

SQLCODE=-204, object not found, Basically the table/schema is not found.

When I ran the same command in debug mode, I could see that in the following class, liquibase/UniqueConstraintSnapshotGenerator.java at master · liquibase/liquibase · GitHub there is no logic to handle DB2z and hence it is considering no specific handler for RDBMS was provided and assuming INFORMATION_SCHEMA.

We do have logic for DB2Database, but not DB2ZDatabase .

## Steps To Reproduce
1. Create a maven project
1. Add the following dependencies in pom.xml
  * com.jbm.db2:db2jcc4 & 4.25.13
  * com.ibm.db2:db2jcc_license_cisuz & 9.7.5
1. Add the following plugin to pom.xml
  * org.liquibase:liquibase-maven-plugin & 4.2.2
  * in the <configuration> tag, add <propertyFile> and specify the property file liquibase-dev.properties to run
1. In the property file liquibase-dev.properties, I specified the follwoing
  * url(jdbc:db2://<hostname>:<port>/currentSchema=<schemaName>;) , username, password, ouputChangeLogFile, driver(com.ibm.db2.jcc.DB2Driver).
1. Run mvn clean and run mvn liquibase:generateChangeLog

## Actual Behavior
When I run mvn liquibase:genereateChangeLog, I'm getting the below error,

Error setting up or running Liquibase: liquibase.command.CommandExcecutionExceptoin: liquibase.exception.DatabaseException: Error executing SQL select CONSTRAINT_NAME, COLUMN_LIST as COLUMN_NAME, constraint_schema as CONSTRAINT_CONTAINER from information_schema.constraints where constraint_type=‘UNIQUE’ and …; DB2 SQL Error: SQLCODE=-204, SQLSTATE=42704, SQLERRMC=INFORMATION_SCHEMA.CONSTRAINTS, DRIVER=4.25.13

## Expected/Desired Behavior
mvn liquibase:generateChangeLog should generate the change log for IBM DB2z based on the current specified database schema.

## Screenshots (if appropriate)
If applicable, add screenshots to help explain your problem.

## Additional Context
Add any other context about the problem here.


}
            Set<String> seenConstraints = new HashSet<>();
            for (CachedRow constraint : metadata) {
                UniqueConstraint uq = new UniqueConstraint()
                        .setName(cleanNameFromDatabase((String) constraint.get("CONSTRAINT_NAME"), database)).setRelation(table);
                if (constraint.containsColumn("INDEX_NAME")) {
                    uq.setBackingIndex(new Index((String) constraint.get("INDEX_NAME"), (String) constraint.get("INDEX_CATALOG"), (String) constraint.get("INDEX_SCHEMA"), table.getName()));
                }
                if ("CLUSTERED".equals(constraint.get("TYPE_DESC"))) {
                    uq.setClustered(true);
                }
                if (seenConstraints.add(uq.getName())) {
                    table.getUniqueConstraints().add(uq);
                }
            }
        }
    }
    protected List<CachedRow> listConstraints(Table table, DatabaseSnapshot snapshot, Schema schema) throws DatabaseException, SQLException {
        return ((JdbcDatabaseSnapshot) snapshot).getMetaDataFromCache().getUniqueConstraints(schema.getCatalogName(), schema.getName(), table.getName());
    }
    protected List<Map<String, ?>> listColumns(UniqueConstraint example, Database database, DatabaseSnapshot snapshot) throws DatabaseException {
        Relation table = example.getRelation();
        Schema schema = table.getSchema();
        String name = example.getName();
        boolean bulkQuery;
        String sql;
        String cacheKey = "uniqueConstraints-" + example.getClass().getSimpleName() + "-" + example.getSchema().toCatalogAndSchema().customize(database).toString();
        String queryCountKey = "uniqueConstraints-" + example.getClass().getSimpleName() + "-queryCount";
        Map<String, List<Map<String, ?>>> columnCache = (Map<String, List<Map<String, ?>>>) snapshot.getScratchData(cacheKey);
        Integer columnQueryCount = (Integer) snapshot.getScratchData(queryCountKey);