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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.


if (columnQueryCount == null) {
            columnQueryCount = 0;
        }
        if (columnCache == null) {
            bulkQuery = false;
            if (columnQueryCount > 3) {
                bulkQuery = supportsBulkQuery(database);
            }
            snapshot.setScratchData(queryCountKey, columnQueryCount + 1);
            if ((database instanceof MySQLDatabase) || (database instanceof HsqlDatabase)) {
                sql = "select const.CONSTRAINT_NAME, const.TABLE_NAME, COLUMN_NAME, const.constraint_schema as CONSTRAINT_CONTAINER "
                        + "from " + database.getSystemSchema() + ".table_constraints const "
                        + "join " + database.getSystemSchema() + ".key_column_usage col "
                        + "on const.constraint_schema=col.constraint_schema "
                        + "and const.table_name=col.table_name "
                        + "and const.constraint_name=col.constraint_name "
                        + "where const.constraint_schema='" + database.correctObjectName(schema.getCatalogName(), Catalog.class) + "' ";
                if (!bulkQuery) {
                    sql += "and const.table_name='" + database.correctObjectName(example.getRelation().getName(), Table.class) + "' "
                            + "and const.constraint_name='" + database.correctObjectName(name, UniqueConstraint.class) + "'";
                }
                sql += "order by ordinal_position";
            } else if (database instanceof PostgresDatabase) {
                sql = "select const.CONSTRAINT_NAME, COLUMN_NAME, const.constraint_schema as CONSTRAINT_CONTAINER "
                        + "from " + database.getSystemSchema() + ".table_constraints const "
                        + "join " + database.getSystemSchema() + ".key_column_usage col "
                        + "on const.constraint_schema=col.constraint_schema "
                        + "and const.table_name=col.table_name "
                        + "and const.constraint_name=col.constraint_name "
                        + "where const.constraint_catalog='" + database.correctObjectName(schema.getCatalogName(), Catalog.class) + "' ";