Add wp db clean command

features/db.feature

@@ -104,6 +104,37 @@ Feature: Perform database operations
       """
     And STDOUT should be empty
 
+  Scenario: Clean up a WordPress install without dropping its database entirely but tables with prefix.
+    Given a WP install
+
+    When I run `wp db query "create table custom_table as select * from wp_users;"`
+    Then STDOUT should be empty
+    And the return code should be 0
+
+    When I run `wp db clean --yes --dbuser=wp_cli_test --dbpass=password1`
+    Then STDOUT should be:
+      """
+      Success: Tables dropped.
+      """
+
+    When I run `wp core install --title="WP-CLI Test" --url=example.com --admin_user=admin --admin_password=admin --admin_email=admin@example.com`
+    Then STDOUT should not be empty
+
+    When I try `wp db clean --yes --dbuser=no_such_user`
+    Then the return code should not be 0
+    And STDERR should contain:
+      """
+      Access denied
+      """
+    And STDOUT should be empty
+
+    When I run `wp db tables custom_table --all-tables`
+    Then STDOUT should be:
+      """
+      custom_table
+      """
+    And the return code should be 0
+
   Scenario: DB Operations
     Given a WP install
 

src/DB_Command.php

@@ -118,6 +118,64 @@ public function reset( $_, $assoc_args ) {
 		WP_CLI::success( "Database reset." );
 	}
 
+	/**
+	 * Removes all tables with `$table_prefix` from the database.
+	 *
+	 * Runs `DROP_TABLE` for each table that has a `$table_prefix` as specified
+	 * in wp-config.php.
+	 *
+	 * ## OPTIONS
+	 *
+	 * [--dbuser=<value>]
+	 * : Username to pass to mysql. Defaults to DB_USER.
+	 *
+	 * [--dbpass=<value>]
+	 * : Password to pass to mysql. Defaults to DB_PASSWORD.
+	 *
+	 * [--yes]
+	 * : Answer yes to the confirmation message.
+	 *
+	 * ## EXAMPLES
+	 *
+	 *     # Delete all tables that match the current site prefix.
+	 *     $ wp db clean --yes
+	 *     Success: Tables dropped.
+	 *
+	 * @when after_wp_load
+	 */
+	public function clean( $_, $assoc_args ) {
+		global $wpdb;
+
+		WP_CLI::confirm(
+			sprintf(
+				"Are you sure you want to drop all the tables on '%s' that use the current site's database prefix ('%s')?",
+				DB_NAME,
+				$wpdb->get_blog_prefix()
+			),
+			$assoc_args
+		);
+
+		$mysql_args = self::get_dbuser_dbpass_args( $assoc_args );
+
+		$tables = WP_CLI\Utils\wp_get_table_names(
+			array(),
+			array( 'all-tables-with-prefix' )
+		);
+
+		foreach ( $tables as $table ) {
+			self::run_query(
+				sprintf(
+					'DROP TABLE IF EXISTS `%s`.`%s`',
+					DB_NAME,
+					$table
+				),
+				$mysql_args
+			);
+		}
+
+		WP_CLI::success( 'Tables dropped.' );
+	}
+
 	/**
 	 * Checks the current status of the database.
 	 *
@@ -744,11 +802,11 @@ public function size( $args, $assoc_args ) {
 						case 'tb':
 						         $divisor = TB_IN_BYTES;
 							 break;
-							
+
 						case 'gb':
 						         $divisor = GB_IN_BYTES;
 							 break;
-							
+
 						case 'mb':
 							$divisor = MB_IN_BYTES;
 							break;
@@ -865,7 +923,7 @@ public function prefix() {
 	 * : Percent color code to use for the match (unless both before and after context are 0, when no color code is used). For a list of available percent color codes, see below. Default '%3%k' (black on a mustard background).
 	 *
 	 * The percent color codes available are:
-	 * 
+	 *
 	 * | Code | Color
 	 * | ---- | -----
 	 * |  %y  | Yellow (dark) (mustard)