What are Liquibase change types and can you name common ones?

A change type is the specific DDL or DML operation that a changeSet performs. Liquibase provides over 40 built-in change types that are database-agnostic — you write the intent (add a column, create an index) and Liquibase generates the correct SQL for the target database. This is one of Liquibase's biggest advantages over raw SQL migrations: the same changeLog can deploy to PostgreSQL, Oracle, MySQL, and SQL Server without modification.

Common structural change types:

• createTable / dropTable — create or drop a table with columns and constraints.
• addColumn / dropColumn — add or remove a column from an existing table.
• renameColumn / renameTable — rename columns or tables without recreating them.
• modifyDataType — change a column's data type.
• addNotNullConstraint / dropNotNullConstraint — add or remove NOT NULL constraints.
• addUniqueConstraint / dropUniqueConstraint — manage unique constraints.
• addForeignKeyConstraint / dropForeignKeyConstraint — manage foreign key relationships.
• createIndex / dropIndex — manage indexes.
• createSequence / dropSequence — manage sequences (for Oracle, PostgreSQL).
• createView / dropView — manage views.

Data change types:

• insert — insert rows into a table.
• update — update existing rows.
• delete — delete rows matching a condition.
• loadData / loadUpdateData — bulk load from a CSV file.

There is also sql and sqlFile for arbitrary SQL when no built-in type covers your needs, though using them gives up the database-agnostic benefit.