In order to show total number of rows in many table we use Information schema which is :
In relational databases, the information schema is an ANSI standard set of read-only views which provide information about all of the tables, views, columns, and procedures in a database. It can be used as a source of the information which some databases make available through non-standard commands, such as the SHOW command of MySQL, the DESCRIBE command of Oracle, and the \d command of PostgreSQL.
Example (total number of rows in a different tables)
SELECT sum(TABLE_ROWS) FROM information_schema.`TABLES` WHERE TABLE_NAME IN ('car' ,'test234') AND TABLE_SCHEMA = 'test'