Drop Table

Basic Table Removal

Use drop_table to remove a table:

DB::Migrate.migrate("remove_old_table", client) do
	drop_table :old_users_table
end

Safe Table Removal

Use if_exists to avoid errors if the table doesn't exist:

DB::Migrate.migrate("safe_cleanup", client) do
	drop_table :maybe_missing_table, if_exists: true
end

Feature Detection

The gem automatically detects whether your database supports IF EXISTS clauses:

PostgreSQL & MariaDB:

DROP TABLE IF EXISTS old_table;

Databases without IF EXISTS support:

DROP TABLE old_table;

Multiple Table Removal

Remove multiple tables in a single migration:

DB::Migrate.migrate("cleanup_old_tables", client) do
	drop_table :temp_users, if_exists: true
	drop_table :old_analytics, if_exists: true
	drop_table :deprecated_logs, if_exists: true
end

Advanced Examples

Conditional Removal

Check if a table exists before dropping it:

DB::Migrate.migrate("conditional_cleanup", client) do
	if information_schema.table_exists?(:old_table)
		drop_table :old_table
	end
end

Table Replacement

Replace an existing table with a new structure:

DB::Migrate.migrate("replace_users_table", client) do
		# Drop the old table
	drop_table :users, if_exists: true
	
		# Create the new table
	create_table :users do
		primary_key
		column :name, "TEXT NOT NULL"
		column :email, "TEXT UNIQUE NOT NULL"
		timestamps
	end
end

Dependent Table Cleanup

Remove tables in the correct order to handle dependencies:

DB::Migrate.migrate("cleanup_related_tables", client) do
		# Drop dependent tables first
	drop_table :user_preferences, if_exists: true
	drop_table :user_sessions, if_exists: true
	
		# Then drop the main table
	drop_table :users, if_exists: true
end

Best Practices

Always Use if_exists for Cleanup

When removing tables during cleanup operations, always use if_exists:

# Good: Safe cleanup
drop_table :temp_table, if_exists: true

# Risky: May fail if table doesn't exist
drop_table :temp_table

Document Destructive Operations

Add clear comments for destructive operations:

DB::Migrate.migrate("remove_deprecated_analytics", client) do
		# WARNING: This permanently removes all analytics data from before 2023
		# Ensure backup is completed before running this migration
	drop_table :old_analytics_2022, if_exists: true
end

Consider Data Migration

Before dropping tables with important data, consider migrating it:

DB::Migrate.migrate("migrate_user_data", client) do
		# First, migrate important data
	session.query("INSERT INTO users_new SELECT id, name, email FROM users_old")
	
		# Then drop the old table
	drop_table :users_old, if_exists: true
end

Safety Considerations

Backup Important Data

Always backup important data before dropping tables:

# PostgreSQL
pg_dump -t old_important_table mydb > backup.sql

# MariaDB/MySQL  
mysqldump mydb old_important_table > backup.sql

Test Migrations

Test destructive migrations on a copy of your production data:

# Test migration on development/staging first
DB::Migrate.migrate("test_table_removal", client) do
	drop_table :test_table, if_exists: true
end

Transaction Safety

Table drops are included in the migration transaction and will be rolled back if any subsequent operation fails:

DB::Migrate.migrate("safe_migration", client) do
	drop_table :old_table, if_exists: true
	
	create_table :new_table do
		primary_key
		column :name, "TEXT NOT NULL"
	end
	
		# If this fails, the table drop above is rolled back
	create_index :new_table, :name
end