实例：
查看某个库的大小
mysql>use information_schema;
mysql>select concat(round(sum(DATA_LENGTH+index_length)/1024/1024,2),'MB') as data_mb,concat(round(sum(DATA_LENGTH/1024/1024),2),'MB') as data_mb,concat(round(sum(index_LENGTH/1024/1024),2),'MB') as index_mb from tables where table_schema='employees';
+----------+----------+----------+
| data_mb | data_mb | index_mb |
+----------+----------+----------+
| 188.44MB | 134.25MB | 54.19MB |
+----------+----------+----------+
1 row in set (0.00 sec)
查看某个库的某个表的大小
select concat(round(sum(DATA_LENGTH+index_length)/1024/1024,2),'MB') as data_mb,concat(round(sum(DATA_LENGTH/1024/1024),2),'MB') as data_mb,concat(round(sum(index_LENGTH/1024/1024),2),'MB') as index_mb from tables where table_schema='employees'and table_name='employees';
----------------------------------------------------------------------------------------------
concat 和round 函数说明
1.round 四余五入函数,如round(2.555)结果为3,round(2.555,2)表示以2位小数来四舍五入,如果为2.56.
可以在终端试一下啊.
select round(2.555,2) from dual;
2.concat
MySQL concat函数使用方法：
CONCAT(str1,str2,…)
返回结果为连接参数产生的字符串。如有任何一个参数为NULL ，则返回值为 NULL。
注意：
如果所有参数均为非二进制字符串，则结果为非二进制字符串。
如果自变量中含有任一二进制字符串，则结果为一个二进制字符串。
一个数字参数被转化为与之相等的二进制字符串格式；若要避免这种情况，可使用显式类型 cast, 例如：
SELECT CONCAT(CAST(int_col AS CHAR), char_col)
MySQL concat函数可以连接一个或者多个字符串,如
mysql> select concat('10');
+--------------+
| concat('10') |
+--------------+
| 10 |
+--------------+
1 row in set (0.00 sec)
mysql> select concat('11','22','33');
+------------------------+
| concat('11','22','33') |
+------------------------+
| 112233 |
+------------------------+
1 row in set (0.00 sec)
MySQL的concat函数在连接字符串的时候，只要其中一个是NULL,那么将返回NULL
mysql> select concat('11','22',null);
+------------------------+
| concat('11','22',null) |
+------------------------+
| NULL |
+------------------------+
1 row in set (0.00 sec)
查看的一般步骤
查看所有库的大小
mysql> use information_schema;
Database changed
mysql> select concat(round(sum(DATA_LENGTH/1024/1024),2),'MB') as data from TABLES;
+----------+
| data |
+----------+
| 104.21MB |
+----------+
1 row in set (0.11 sec)
查看指定库的大小
mysql> select concat(round(sum(DATA_LENGTH/1024/1024),2),'MB') as data from TABLES where table_schema='jishi';
+---------+
| data |
+---------+
| 26.17MB |
+---------+
1 row in set (0.01 sec)
查看指定库的指定表的大小
mysql> select concat(round(sum(DATA_LENGTH/1024/1024),2),'MB') as data from TABLES where table_schema='jishi' and table_name='a_ya';
+--------+
| data |
+--------+
| 0.02MB |
+--------+
1 row in set (0.00 sec)
查看指定库的索引大小
mysql> SELECT CONCAT(ROUND(SUM(index_length)/(1024*1024), 2), ' MB') AS 'Total Index Size' FROM TABLES WHERE table_schema = 'jishi';
+------------------+
| Total Index Size |
+------------------+
| 0.94 MB |
+------------------+
1 row in set (0.01 sec)
查看指定库的指定表的索引大小
mysql> SELECT CONCAT(ROUND(SUM(index_length)/(1024*1024), 2), ' MB') AS 'Total Index Size' FROM TABLES WHERE table_schema = 'test' and table_name='a_yuser';
+------------------+
| Total Index Size |
+------------------+
| 21.84 MB |
+------------------+
1 row in set (0.00 sec)
mysql> show create table test.a_yuser\G;
*************************** 1. row ***************************
Table: a_yuser
Create Table: CREATE TABLE `a_yuser` (
`email` varchar(60) NOT NULL DEFAULT '',
`user_name` varchar(60) NOT NULL DEFAULT '',
KEY `cc` (`email`(5)),
KEY `ccb` (`user_name`(5)),
KEY `ccbc` (`email`(5),`user_name`(5))
) ENGINE=MyISAM DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
ERROR:
No query specified
mysql> select count(*) from test.a_yuser;
+----------+
| count(*) |
+----------+
| 1073607 |
+----------+
1 row in set (0.00 sec)
mysql>
查看一个库中的情况...
mysql> SELECT CONCAT(table_schema,'.',table_name) AS 'Table Name', CONCAT(ROUND(table_rows/1000000,4),'M') AS 'Number of Rows', CONCAT(ROUND(data_length/(1024*1024*1024),4),'G') AS 'Data Size', CONCAT(ROUND(index_length/(1024*1024*1024),4),'G') AS 'Index Size', CONCAT(ROUND((data_length+index_length)/(1024*1024*1024),4),'G') AS'Total'FROM information_schema.TABLES WHERE table_schema LIKE 'test';
+---------------+----------------+-----------+------------+---------+
| Table Name | Number of Rows | Data Size | Index Size | Total |
+---------------+----------------+-----------+------------+---------+
| test.a_br | 0.4625M | 0.0259G | 0.0171G | 0.0431G |
| test.a_skuclr | 0.7099M | 0.0660G | 0.0259G | 0.0919G |
| test.a_yuser | 1.0736M | 0.0497G | 0.0213G | 0.0710G |
| test.test | 0.0000M | 0.0000G | 0.0000G | 0.0000G |
+---------------+----------------+-----------+------------+---------+
