mysqldiff对数据库间进行差异比较

  mysqldiff该工具是官方mysql-utilities工具集的一个脚本，可以用来对比不同数据库之间的表结构，或者同个数据库间的表结构
   如果在windows下，直接下载mysql-utilities安装就可以了，然后运行后，会跑到命令行下：

1） 基本用法
   mysqldiff --server1=admin:[email protected] --server2=admin:[email protected]
--difftype=differ test:test

  这样就比较两个不同库中的数据库test，假设两个库中库名都是test
也可以比较不同的表

mysqldiff --server1=user@host1 --server2=user@host2 testdb.table1:anotherdb.anothertable
     就是使用库名.表名的方式就可以了

  下面是出来的一个效果

# mysqldiff --force --server1=root:[email protected]:21489 --server2=root:[email protected]:21490 employees:employees
# WARNING: Using a password on the command line interface can be insecure.
# server1 on 127.0.0.1: ... connected.
# server2 on 127.0.0.1: ... connected.
# Comparing `employees` to `employees`                             [PASS]
# Comparing `employees`.`departments` to `employees`.`departments`   [FAIL]
# Object definitions differ. (--changes-for=server1)
#
--- `employees`.`departments`
+++ `employees`.`departments`
@@ -1,6 +1,6 @@
CREATE TABLE `departments` (
   `dept_no` char(4) NOT NULL,
-  `dept_name` varchar(40) NOT NULL,
+  `dept_name` varchar(256) DEFAULT NULL,
   PRIMARY KEY (`dept_no`),
   UNIQUE KEY `dept_name` (`dept_name`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1



  可以看到，默认-号代表左边要比较的server1的变化，+号代表右边server2的不同，
如果要交换，可以使用参数：
    –changes-for=server2

  如果要在比较不同的时候，强行继续比较下去，要增加--force选项

2） 可以生成差异化的SQL，因为方法1）中，只产生了不同的地方，但如为了生产考虑，
要生成达到server2的脚本，则可以使用参数
  --difftype=sql，
则：
  mysqldiff --server1=admin:[email protected] --server2=admin:[email protected]
--difftype=sql test:test

mysqldiff的核心是使用INFORMATION_SCHEMA

SHOW CREATE TABLE `departments`;
SELECT TABLE_SCHEMA, TABLE_NAME, ENGINE, AUTO_INCREMENT, AVG_ROW_LENGTH, CHECKSUM, TABLE_COLLATION, TABLE_COMMENT, ROW_FORMAT, CREATE_OPTIONS
  FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA = 'employees' AND TABLE_NAME = 'departments';
SELECT ORDINAL_POSITION, COLUMN_NAME, COLUMN_TYPE, IS_NULLABLE,
         COLUMN_DEFAULT, EXTRA, COLUMN_COMMENT, COLUMN_KEY
  FROM INFORMATION_SCHEMA.COLUMNS
  WHERE TABLE_SCHEMA = 'employees' AND TABLE_NAME = 'departments';
SELECT PARTITION_NAME, SUBPARTITION_NAME, PARTITION_ORDINAL_POSITION,
         SUBPARTITION_ORDINAL_POSITION, PARTITION_METHOD, SUBPARTITION_METHOD,
         PARTITION_EXPRESSION, SUBPARTITION_EXPRESSION, PARTITION_DESCRIPTION
  FROM INFORMATION_SCHEMA.PARTITIONS
  WHERE TABLE_SCHEMA = 'employees' AND TABLE_NAME = 'departments';
SELECT CONSTRAINT_NAME, COLUMN_NAME, REFERENCED_TABLE_SCHEMA,
         REFERENCED_TABLE_NAME, REFERENCED_COLUMN_NAME
  FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE
  WHERE TABLE_SCHEMA = 'employees' AND TABLE_NAME = 'departments' AND
        REFERENCED_TABLE_SCHEMA IS NOT NULL;
SELECT TABLE_SCHEMA, TABLE_NAME, ENGINE, AUTO_INCREMENT, AVG_ROW_LENGTH, CHECKSUM, TABLE_COLLATION, TABLE_COMMENT, ROW_FORMAT, CREATE_OPTIONS
  FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA = 'employees' AND TABLE_NAME = 'departments';
SELECT ORDINAL_POSITION, COLUMN_NAME, COLUMN_TYPE, IS_NULLABLE,
         COLUMN_DEFAULT, EXTRA, COLUMN_COMMENT, COLUMN_KEY
  FROM INFORMATION_SCHEMA.COLUMNS
  WHERE TABLE_SCHEMA = 'employees' AND TABLE_NAME = 'departments';
SELECT PARTITION_NAME, SUBPARTITION_NAME, PARTITION_ORDINAL_POSITION,
         SUBPARTITION_ORDINAL_POSITION, PARTITION_METHOD, SUBPARTITION_METHOD,
         PARTITION_EXPRESSION, SUBPARTITION_EXPRESSION, PARTITION_DESCRIPTION
  FROM INFORMATION_SCHEMA.PARTITIONS
  WHERE TABLE_SCHEMA = 'employees' AND TABLE_NAME = 'departments';

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