就ADO而言,nvarchar(max)有多大? [英] How big is an nvarchar(max) as far as ADO is concerned?
问题描述
我正在尝试使用针对ADO的参数化查询:
INSERT INTO Foo(名称,值)VALUES(@ name,@ value)
INSERT INTO Foo (Name, Value) VALUES(@name, @value)
在SQL Server中,名称
列为 varchar
类型。 Value
列是 nvarchar(max)
。
In SQL Server the Name
column is a varchar
type. The Value
column is an nvarchar(max)
.
在我不知道或不想指定大小的情况下创建参数时,我要传递什么 size ?
What size do i pass when creating a parameter when i don't know, or want to specify, the size?
procedure SaveTheThing(Connection: TADOConnection);
var
sql: WideString;
cmd: _Command;
begin
sql := 'INSERT INTO Foo (Name, Value) VALUES(@name, @value)';
cmd := CoCommand.Create;
cmd.Set_ActiveConnection(Connection.ConnectionObject);
cmd.Set_CommandType(adCmdText);
cmd.Set_CommandText(sql);
//and now add the parameters
cmd.Parameters.Append(
cmd.CreateParameter('@name', adVarChar, adParamInput, -1, filename)
);
cmd.Parameters.Append(
cmd.CreateParameter('@value', adVarWChar, adParamInput, -1, GetXmlToWideString)
);
cmd.Execute({out}recordsAffected, EmptyParam, adCmdSomeThatDoesntCauseAnExcetpion or adExecuteNoRecords);
end;
简单的选择是:
sql := 'INSERT INTO Foo (Name, Value)'#13#10+
'VALUES (+QuotedStr(filename)+', '+QuotedStrW(GetXmlToWideString)+')';
,并且已经完成。但我认为我会花几天时间尝试使参数化查询成为可行的解决方案,并且避免编写 QuotedStrW
。
and be done already. But i thought i'd burn a few days trying to make parameterized queries a viable solution, and avoid having to write a QuotedStrW
.
推荐答案
ADO参数大小的 -1
值没有问题。
You can use the -1
value in the size of a ADO parameter without problems.
尝试以下示例代码,该示例代码插入一个值
列中的2MB字符串
Try this sample code , which insert a 2MB string in the Value
column
var
sql: WideString;
cmd: _Command;
recordsAffected : OleVariant;
begin
sql := 'INSERT INTO Foo (Name, Value) VALUES(?, ?)';
cmd := CoCommand.Create;
cmd.Set_ActiveConnection(Connection.ConnectionObject);
cmd.Set_CommandType(adCmdText);
cmd.Set_CommandText(sql);
//and now add the parameters
cmd.Parameters.Append(cmd.CreateParameter('@name', adVarChar, adParamInput, -1, 'AfileName'));
cmd.Parameters.Append(cmd.CreateParameter('@value', adVarWChar, adParamInput, -1, StringOfChar('#', 2*1024*1024)));
cmd.Execute({out}recordsAffected, EmptyParam, adExecuteNoRecords);
end;
这篇关于就ADO而言,nvarchar(max)有多大?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!