DbCommand.ExecuteScalar DbCommand.ExecuteScalar DbCommand.ExecuteScalar DbCommand.ExecuteScalar Method

定义

当在派生类中重写时,执行查询,并将查询返回的结果集中第一行的第一列返回。When overridden in a derived class, executes the query and returns the first column of the first row in the result set returned by the query. 所有其他的列和行将被忽略。All other columns and rows are ignored.

public:
 abstract System::Object ^ ExecuteScalar();
public abstract object ExecuteScalar ();
abstract member ExecuteScalar : unit -> obj
Public MustOverride Function ExecuteScalar () As Object

返回

结果集中第一行的第一列。The first column of the first row in the result set.

实现

注解

ExecuteScalar使用方法从数据库中检索单个值(例如聚合值)。Use the ExecuteScalar method to retrieve a single value (for example, an aggregate value) from a database. 这需要比使用ExecuteReader方法更少的代码,并使用DbDataReader由返回的数据执行生成单个值所需的操作。This requires less code than using the ExecuteReader method and performing the operations necessary to generate the single value using the data returned by a DbDataReader.

如果找不到结果集中第一行的第一列,则返回 null 引用(Nothing在 Visual Basic 中)。If the first column of the first row in the result set is not found, a null reference (Nothing in Visual Basic) is returned. 如果数据库中的值为null,则查询返回。 DBNull.ValueIf the value in the database is null, the query returns DBNull.Value.

适用于

另请参阅