如果你知道表的数量和它们的名称，并且假设它们每个都有主键，你可以使用交叉连接结合COUNT(distinct [column])来获得来自每个表的行:

SELECT 
   COUNT(distinct t1.id) + 
   COUNT(distinct t2.id) + 
   COUNT(distinct t3.id) AS totalRows
FROM firstTable t1, secondTable t2, thirdTable t3;

下面是一个SQL Fiddle的例子。

这个存储过程列出表，统计记录，并在最后生成记录的总数。

添加此过程后运行:

CALL `COUNT_ALL_RECORDS_BY_TABLE` ();

-

过程:

DELIMITER $$

CREATE DEFINER=`root`@`127.0.0.1` PROCEDURE `COUNT_ALL_RECORDS_BY_TABLE`()
BEGIN
DECLARE done INT DEFAULT 0;
DECLARE TNAME CHAR(255);

DECLARE table_names CURSOR for 
    SELECT table_name FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA = DATABASE();

DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;

OPEN table_names;   

DROP TABLE IF EXISTS TCOUNTS;
CREATE TEMPORARY TABLE TCOUNTS 
  (
    TABLE_NAME CHAR(255),
    RECORD_COUNT INT
  ) ENGINE = MEMORY; 


WHILE done = 0 DO

  FETCH NEXT FROM table_names INTO TNAME;

   IF done = 0 THEN
    SET @SQL_TXT = CONCAT("INSERT INTO TCOUNTS(SELECT '" , TNAME  , "' AS TABLE_NAME, COUNT(*) AS RECORD_COUNT FROM ", TNAME, ")");

    PREPARE stmt_name FROM @SQL_TXT;
    EXECUTE stmt_name;
    DEALLOCATE PREPARE stmt_name;  
  END IF;

END WHILE;

CLOSE table_names;

SELECT * FROM TCOUNTS;

SELECT SUM(RECORD_COUNT) AS TOTAL_DATABASE_RECORD_CT FROM TCOUNTS;

END

像@Venkatramanan和其他人一样，我找到了INFORMATION_SCHEMA。TABLES不可靠(使用InnoDB, MySQL 5.1.44)，每次运行时给出不同的行数，即使是在静态表上。这里有一种生成大型SQL语句的相对hack(但是灵活/适应性强)的方法，您可以将其粘贴到新的查询中，而不需要安装Ruby宝石之类的东西。

SELECT CONCAT(
    'SELECT "', 
    table_name, 
    '" AS table_name, COUNT(*) AS exact_row_count FROM `', 
    table_schema,
    '`.`',
    table_name, 
    '` UNION '
) 
FROM INFORMATION_SCHEMA.TABLES 
WHERE table_schema = '**my_schema**';

它产生如下输出:

SELECT "func" AS table_name, COUNT(*) AS exact_row_count FROM my_schema.func UNION                         
SELECT "general_log" AS table_name, COUNT(*) AS exact_row_count FROM my_schema.general_log UNION           
SELECT "help_category" AS table_name, COUNT(*) AS exact_row_count FROM my_schema.help_category UNION       
SELECT "help_keyword" AS table_name, COUNT(*) AS exact_row_count FROM my_schema.help_keyword UNION         
SELECT "help_relation" AS table_name, COUNT(*) AS exact_row_count FROM my_schema.help_relation UNION       
SELECT "help_topic" AS table_name, COUNT(*) AS exact_row_count FROM my_schema.help_topic UNION             
SELECT "host" AS table_name, COUNT(*) AS exact_row_count FROM my_schema.host UNION                         
SELECT "ndb_binlog_index" AS table_name, COUNT(*) AS exact_row_count FROM my_schema.ndb_binlog_index UNION 

复制粘贴，除了最后一个UNION，可以得到漂亮的输出，

+------------------+-----------------+
| table_name       | exact_row_count |
+------------------+-----------------+
| func             |               0 |
| general_log      |               0 |
| help_category    |              37 |
| help_keyword     |             450 |
| help_relation    |             990 |
| help_topic       |             504 |
| host             |               0 |
| ndb_binlog_index |               0 |
+------------------+-----------------+
8 rows in set (0.01 sec)

下面的查询生成一个(另一个)查询，该查询将从information_schema.tables中列出的每个模式中获取每个表的count(*)值。这里显示的查询的整个结果——所有行放在一起——包含一个以分号结尾的有效SQL语句——没有悬空的“联合”。在下面的查询中使用联合来避免悬空联合。

select concat('select "', table_schema, '.', table_name, '" as `schema.table`,
                          count(*)
                 from ', table_schema, '.', table_name, ' union ') as 'Query Row'
  from information_schema.tables
 union
 select '(select null, null limit 0);';

如果你使用数据库information_schema，你可以使用下面的mysql代码(where部分使查询不显示行为空值的表):

SELECT TABLE_NAME, TABLE_ROWS
FROM `TABLES`
WHERE `TABLE_ROWS` >=0

 SELECT TABLE_NAME,SUM(TABLE_ROWS) 
 FROM INFORMATION_SCHEMA.TABLES 
 WHERE TABLE_SCHEMA = 'your_db' 
 GROUP BY TABLE_NAME;

这就是你所需要的。