辛星淺談mysql中的元數據

辛星淺談mysql中的元數據

首先解釋一下什麼是元數據，所謂元數據，就是表示數據的數據，這些數據五花八門，總之，只要不是我們存儲到數據庫裡的數據，大多都可以理解為元數據。那麼我們如何來獲取這些元數據呢？

總的來說，有三種思路，第一種，各種show，第二種，各種select，第三種，是mysql的命令行下的命令，不是sql語句。

我們首先看第一種，這裡我列舉一下大家比較熟悉的show語句的用法，其實咱們經常用show來查看信息，比如：

show databases;
show tales;
show create table 表名;
show index from 表名;
....等等

第二種就是通過select來從mysql數據庫或者information_schema數據庫中提取相關信息，比如可以從tables這個表裡面的free_data字段來查看數據碎片的相關信息，這裡我上一篇博文已經介紹過了，這裡就不廢話了。

第三種就是通過mysql自帶的一些命令來查看，這個需要咱們的用戶名和密碼的，下面是我查看相應元數據的代碼，希望能幫到您：

Microsoft Windows [版本 6.1.7601]
版權所有 (c) 2009 Microsoft Corporation。保留所有權利。

C:\Users\Administrator>mysqlshow -u root -proot
mysqlshow: [Warning] Using a password on the command line interface can be insecure.
+--------------------+
|     Databases      |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| test               |
| xinxing            |
+--------------------+

C:\Users\Administrator>mysqlshow -u root -proot xinxing
mysqlshow: [Warning] Using a password on the command line interface can be insecure.
Database: xinxing
+--------+
| Tables |
+--------+
| xin    |
+--------+

C:\Users\Administrator>mysqlshow -u root -proot --status xinxing
mysqlshow: [Warning] Using a password on the command line interface can be insecure.
Database: xinxing
+------+--------+---------+------------+------+----------------+-------------+-------------------+--------------+-------
----+----------------+---------------------+---------------------+---------------------+-----------------+----------+---
-------------+---------+
| Name | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length   | Index_length | Data_f
ree | Auto_increment | Create_time         | Update_time         | Check_time          | Collation       | Checksum | Cr
eate_options | Comment |
+------+--------+---------+------------+------+----------------+-------------+-------------------+--------------+-------
----+----------------+---------------------+---------------------+---------------------+-----------------+----------+---
-------------+---------+
| xin  | MyISAM | 10      | Fixed      | 3    | 121            | 363         | 34058472181989375 | 1024         | 0
    |                | 2014-08-25 13:19:02 | 2014-08-25 13:41:25 | 2014-08-25 13:41:25 | utf8_general_ci |          |
             |         |
+------+--------+---------+------------+------+----------------+-------------+-------------------+--------------+-------
----+----------------+---------------------+---------------------+---------------------+-----------------+----------+---
-------------+---------+

C:\Users\Administrator>

下面是我用mysqldump來查看表結構的一些操作，希望對您有用：

C:\Users\Administrator>mysqldump -u root -proot --no-data xinxing xin
mysqldump: [Warning] Using a password on the command line interface can be insecure.
-- MySQL dump 10.13  Distrib 5.7.3-m13, for Win64 (x86_64)
--
-- Host: localhost    Database: xinxing
-- ------------------------------------------------------
-- Server version       5.7.3-m13

/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;
/*!40101 SET NAMES utf8 */;
/*!40103 SET @OLD_TIME_ZONE=@@TIME_ZONE */;
/*!40103 SET TIME_ZONE='+00:00' */;
/*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */;
/*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;
/*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;
/*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */;

--
-- Table structure for table `xin`
--

DROP TABLE IF EXISTS `xin`;
/*!40101 SET @saved_cs_client     = @@character_set_client */;
/*!40101 SET character_set_client = utf8 */;
CREATE TABLE `xin` (
  `c` char(40) DEFAULT NULL
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
/*!40101 SET character_set_client = @saved_cs_client */;
/*!40103 SET TIME_ZONE=@OLD_TIME_ZONE */;

/*!40101 SET SQL_MODE=@OLD_SQL_MODE */;
/*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */;
/*!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS */;
/*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;
/*!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS */;
/*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */;
/*!40111 SET SQL_NOTES=@OLD_SQL_NOTES */;

-- Dump completed on 2014-08-25 20:49:08

辛星，期待您的關注。。