C# 使用 select 语句后将值存储在变量中
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Store value in a variable after using select statement
提问by user175084
How to store the value of the PolicyIDreturned from database in an integer variable in C#?
如何PolicyID将从数据库返回的值存储在整数变量中C#？
I am using SQL server 2005.
我正在使用 SQL Server 2005。
System.Data.SqlClient.SqlConnection dataConnection = new SqlConnection();
dataConnection.ConnectionString =
@"Data Source=JAGMIT-PC\SQLEXPRESS;Initial Catalog=SumooHAgentDB;Integrated Security=True";
System.Data.SqlClient.SqlCommand dataCommand = new SqlCommand();
dataCommand.Connection = dataConnection;
dataCommand.CommandText = ("select PolicyID from Policies where PolicyID=(select max(PolicyID) from Policies)");
dataConnection.Open();
dataCommand.ExecuteNonQuery();
dataConnection.Close();
Please suggest.
请建议。
Thanks.
谢谢。
采纳答案by SLaks
Use the SqlCommand.ExecuteScalarmethod, like this:
使用SqlCommand.ExecuteScalar方法，如下所示：
command.CommandText = @"select max(PolicyID) from Policies";
int maxPolicyId = (int)command.ExecuteScalar();
Also, if you're doing this to insert a new Policy row with a unique ID, you must not do it like this, because it's entirely possible that a different Policies row will be inserted between the select and the insert.
此外，如果您这样做是为了插入一个具有唯一 ID 的新 Policy 行，则不能这样做，因为完全有可能在 select 和 insert 之间插入不同的 Policies 行。
Instead, use an IDENTITYcolumn or a UNIQUEIDENTIFIERcolumn.
而是使用一IDENTITY列或一UNIQUEIDENTIFIER列。
EDIT: To use this in your code, do this:
编辑：要在您的代码中使用它，请执行以下操作：
int maxId;
using (SqlConnection dataConnection = new SqlConnection(@"Data Source=JAGMIT-PC\SQLEXPRESS;Initial Catalog=SumooHAgentDB;Integrated Security=True"))
using (SqlCommand dataCommand =
new SqlCommand("select max(PolicyID) from Policies", dataConnection)) {
dataConnection.Open();
maxId = Convert.ToInt32(dataCommand.ExecuteScalar());
}
回答by Gary McGill
DECLARE @id INTEGER
SELECT @id=PolicyID FROM ...
回答by Hans Ke?ing
Did you just insert a new record into that policy table and now you want the ID given? Then instead of a max(), use
您是否刚刚在该策略表中插入了一条新记录，现在您想要给定 ID？然后，而不是 max()，使用
SELECT SCOPY_IDENTITY()
to get the value that was assigned to yourrecord, not to a record that happened to be inserted moments later.
获取分配给您的记录的值，而不是稍后插入的记录。
回答by oscaro
You can also use SELECT IDENT_CURRENT('Policies')to get the value that was created for your record. To learn more about the differences between SCOPE_IDENTITY()AND IDENT_CURRENT('tablename'), check out this link.
您还可以使用SELECT IDENT_CURRENT('Policies')获取为您的记录创建的值。要了解有关SCOPE_IDENTITY()AND之间差异的更多信息IDENT_CURRENT('tablename')，请查看此链接。
