元数据 (metadata) 最常见的定义为"有关数据的结构数据"，或者再简单一点就是"关于数据的信息"，日常生活中的图例、图书馆目录卡和名片等都可以看作是元数据。在关系型数据库管理系统 (DBMS) 中，元数据描述了数据的结构和意义。比如在管理、维护 SQL Server 或者是开发数据库应用程序的时候，我们经常要获取一些涉及到数据库架构的信息：

常用的信息架构视图有以下一些：

由于这些信息架构都是以视图的方式存在的，因此我们可以很方便地获得并利用需要的信息。

所以很容易的利用数据库元数据信息实现ORM功能，下面是几个常用的SQL

       //获取表的所有列
       public const string TABLE_COLUMN_SQL = " SELECT     TABLE_CATALOG AS [Database], TABLE_SCHEMA AS Owner, TABLE_NAME AS TableName, COLUMN_NAME AS ColumnName,  " +
                          "ORDINAL_POSITION AS OrdinalPosition, COLUMN_DEFAULT AS DefaultSetting, IS_NULLABLE AS IsNullable, DATA_TYPE AS DataType,  " +
                          "CHARACTER_MAXIMUM_LENGTH AS MaxLength, NUMERIC_PRECISION AS Precision, DATETIME_PRECISION AS DatePrecision " +
                           "FROM         INFORMATION_SCHEMA.COLUMNS " +
                           "WHERE     (TABLE_NAME = @tblName) ";

         //获取表的所有存储过程和参数
         public const string SP_PARAM_SQL="SELECT     SPECIFIC_CATALOG AS [Database], SPECIFIC_SCHEMA AS Owner, SPECIFIC_NAME AS SPName, ORDINAL_POSITION AS OrdinalPosition,  " +
                       "PARAMETER_MODE AS ParamType, IS_RESULT AS IsResult, PARAMETER_NAME AS Name, DATA_TYPE AS DataType,  " +
                       "CHARACTER_MAXIMUM_LENGTH AS DataLength, REPLACE(PARAMETER_NAME, '@', '') AS CleanName " +
                       "FROM         INFORMATION_SCHEMA.PARAMETERS " +
                       "WHERE SPECIFIC_NAME=@spName";

        //获取表的所有存储过程的Sql
         public const string SP_SQL = " SELECT     SPECIFIC_CATALOG AS [Database], SPECIFIC_SCHEMA AS Owner, SPECIFIC_NAME AS Name, ROUTINE_DEFINITION AS SQL, CREATED AS CreatedOn, " +
                          "LAST_ALTERED AS ModifiedOn " +
                          "FROM         INFORMATION_SCHEMA.ROUTINES " +
                           "WHERE     (SPECIFIC_NAME = @spName) ";

      //获取表的所有存储过程 
      public const string TABLE_SQL = "SELECT     TABLE_CATALOG AS [Database], TABLE_SCHEMA AS Owner, TABLE_NAME AS Name, TABLE_TYPE "+
             "FROM         INFORMATION_SCHEMA.TABLES "+
                "WHERE     (TABLE_TYPE = 'BASE TABLE') AND (TABLE_NAME <> N'sysdiagrams') " +
             "AND TABLE_NAME=@tblName";

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