How do Flyway and Liquibase tools work
You start from an empty database model, for which the tool specific database control table is empty, no scripts deployed. Then you deploy some scripts, Script1 and Script2, ending up with version 1 of the database.Additional scripts 3 and 4 are registered against the version control table as version 2 of the database. You always know the author name, the script name, the checksum of the script.
Modifiying existing script instead of providing incremental script
Prevention of situations when a script that was applied on a database was modified in version control instead of adding an incremental script
baselining
if your database schema was already created without the usage of any of these tools and you want to start deployments with them at a later time, you can use the baselining commands to create the schema baseline on top of which incremental scripts can be added. The baseline will include the DDLs but not the data.
