SELECT SUM(TABLE_ROWS) 
     FROM INFORMATION_SCHEMA.TABLES 
     WHERE TABLE_SCHEMA = '{your_db}';

文档中的注释: 对于 InnoDB表，行数只是用于 SQL 优化的粗略估计.您需要使用 COUNT(*) 进行精确计数(这更昂贵).

Note from the docs though: For InnoDB tables, the row count is only a rough estimate used in SQL optimization. You'll need to use COUNT(*) for exact counts (which is more expensive).