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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.


"AND [c].[column_id] = [ic].[column_id] " +
                                    "WHERE [s].[name] = N'" + database.escapeStringForDatabase(database.correctObjectName(schema.getName(), Schema.class)) + "' ";
                    if (!bulkQuery) {
                        sql += "AND [t].[name] = N'" + database.escapeStringForDatabase(database.correctObjectName(example.getRelation().getName(), Table.class)) + "' " +
                                "AND [kc].[name] = N'" + database.escapeStringForDatabase(database.correctObjectName(name, UniqueConstraint.class)) + "' ";
                    }
                    sql += "ORDER BY " +
                            "[ic].[key_ordinal]";
            } else if (database instanceof OracleDatabase) {
                sql = "select ucc.owner as constraint_container, ucc.constraint_name as constraint_name, ucc.column_name, f.validated as constraint_validate " +
                        "from all_cons_columns ucc " +
                        "INNER JOIN all_constraints f " +
                        "ON ucc.owner = f.owner " +
                        "AND ucc.constraint_name = f.constraint_name " +
                        "where " +
                        (bulkQuery ? "" : "ucc.constraint_name='" + database.correctObjectName(name, UniqueConstraint.class) + "' and ") +
                        "ucc.owner='" + database.correctObjectName(schema.getCatalogName(), Catalog.class) + "' " +
                        "and ucc.table_name not like 'BIN$%' " +
                        "order by ucc.position";
            } else if (database instanceof DB2Database) {
                if (database.getDatabaseProductName().startsWith("DB2 UDB for AS/400")) {
                    sql = "select T1.constraint_name as CONSTRAINT_NAME, T2.COLUMN_NAME as COLUMN_NAME, T1.CONSTRAINT_SCHEMA as CONSTRAINT_CONTAINER from QSYS2.TABLE_CONSTRAINTS T1, QSYS2.SYSCSTCOL T2\n"
                            + "where T1.CONSTRAINT_TYPE='UNIQUE' and T1.CONSTRAINT_NAME=T2.CONSTRAINT_NAME\n"
                            + "and T1.CONSTRAINT_SCHEMA='" + database.correctObjectName(schema.getName(), Schema.class) + "'\n"
                            + "and T2.CONSTRAINT_SCHEMA='" + database.correctObjectName(schema.getName(), Schema.class) + "'\n"
                            
                            
                            + "order by T2.COLUMN_NAME\n";
                } else {
                    sql = "select k.constname as constraint_name, k.colname as column_name from syscat.keycoluse k, syscat.tabconst t "