sql-server - 为什么 UPDATE .WRITE() 仅在我使用 [column].WRITE() 时才有效，而不是 [table].[column].WRITE()？

Question

我正在执行 UPDATE .WRITE() 语句，并发现它显然只有在您像这样定义它时才有效:

string sql = "UPDATE [dbo].[Table] SET [Column].WRITE(@data, @offset, @count) WHERE ...";
...
sqlCommand.ExecuteNonQuery();

但是，如果我使用 [dbo].[Table].[Column].WRITE(...) 或 [Table].[Column].WRITE(... )，抛出异常:

Incorrect syntax near 'WRITE'.

Stack trace:
   at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection)
   at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj)
   at System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj)
   at System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString)
   at System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async)
   at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, DbAsyncResult result)
   at System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(DbAsyncResult result, String methodName, Boolean sendToPipe)
   at System.Data.SqlClient.SqlCommand.ExecuteNonQuery()
   ...

这是为什么呢？它似乎与构建 SQL 语句的通常方式不太一致。这种看似特殊的约定有什么意义吗？显然不允许您显式指定表名称和架构？

Answer 1

It doesn't seem very consistent ...

它实际上与 SET clause 的其余部分一致:

SET
    { column_name = { expression | DEFAULT | NULL }
      | { udt_column_name.{ { property_name = expression
                            | field_name = expression }
                            | method_name ( argument [ ,...n ] )
                          }
      }
      | column_name { .WRITE ( expression , @Offset , @Length ) }
      | @variable = expression
      | @variable = column = expression
      | column_name { += | -= | *= | /= | %= | &= | ^= | |= } expression
      | @variable { += | -= | *= | /= | %= | &= | ^= | |= } expression
      | @variable = column { += | -= | *= | /= | %= | &= | ^= | |= } expression
    } [ ,...n ] 

也就是说，在 SET 子句中，在赋值的左侧指定表或架构是永远有效的(当然，您可以引用其他表的全名或别名，在右侧的表达式中)。要更新的表已在 UPDATE 和 SET 之间标识。