sqlcommand

问题 I have a custom data type called StudentID , which has an implicit conversion to string. When I pass a StudentID instance to SqlCommand.Parameters.AddWithValue (as the value) and execute the command, I receive the following error: No mapping exists from object type StudentID to a known managed provider native type. Specifying a type for the parameter like SqlDbType.NVarChar doesn't help. The only thing that works is to explicitly cast the StudentID value to a string, which defeats the purpose

问题 I have two tables named User and ParentUser that there is an one to many relation between them and the many side is the ParentUser table. I wanna write a query to pass a parentId and fetch all of its children and a column name HasChildren to see whether every child has any children or not. The picture below shows some sample data and needed result: Tries: 1-By Prdp SELECT u.*, CASE WHEN p.ParentId IS NULL THEN 1 ELSE 0 END as HasChildren FROM [User] u LEFT JOIN (select distinct ParentId from

问题 I have set a column name to "group", which turned out to be a reserved word. Now I try to change the name to "group_code", but I get an error. I try: ALTER TABLE task_values CHANGE group group_code VARCHAR(40) NOT NULL; and ALTER TABLE task_values CHANGE 'group' group_code VARCHAR(40) NOT NULL; but both fail, I get "No such element" error. Please help 回答1: You will need to use backticks around group which, as you said, is a mysql reserved keyword ALTER TABLE task_values CHANGE `group` group

问题 This question already has answers here : Pass Array Parameter in SqlCommand (11 answers) Closed 4 years ago . string idVariable = "qwerty"; string sqlQuery = "select id from user where id = @id"; sqlCommand.Parameters.Add("@id", SqlDbType.VarChar).Value = idVariable; Adding a value for a specific field is ok. What if I need to have a few ids and IN in WHERE clause? List<string> ids = new List<string>{"qwe", "asd", "zxc"}; string sqlQuery = "select id from user where id IN @ids"; sqlCommand

问题 Something stopped working in my application. I tested my stored procedure and it does return 3 rows (too big to repost here). At the output in Visual Studio it says afterwards: (1 row(s) affected) (3 row(s) returned) @RETURN_VALUE = 0 Finished running [dbo].[GetCaseDocumentFile]. Why can't I put it into the datatable called dtResult? The command sqlDataAdapter.Fill(dtResult) should do it. Instead I get {} when looking at it in debug mode. string connectionString = @"Data Source=34.56.55.251

问题 I have two queries: Q1: select name from presidents where country = 'USA' Q2: select 'Obama' as name from presidents where country = 'USA' When using System.Data.Odbc.OdbcCommandExecuteReader then the returned DbDataReader contains 'Obama' in case of Q1 and 'Obama ' in case of Q2. Why is the string padded with trailing spaces in case of Q2 and what is the remedy? Trimming is ugly and even wrong in some cases. I am using .Net Framework 3.5. Here is the test code OdbcCommand cmd = new

问题 When I run the following snippet try { using (SqlConnection conn = new SqlConnection("I'm shy")) { conn.Open(); using (SqlCommand cmd = conn.CreateCommand()) { cmd.CommandText = "PRINT 'A';PRINT 'B';PRINT 'C';RAISERROR('SQL_Error', 18, 1)"; cmd.ExecuteNonQuery(); } } } catch (SqlException ex) { MessageBox.Show(ex.Message); } I get the following message: SQL_Error A B C and ex.Errors has 4 entries (The 3 SqlError 's corresponding to the prints have a SqlError.Class of 0 (vs. 18 for the real

问题 The default CommandTimeout value is 30 seconds. You can manually change the value on an instance of the command object by doing the following Dim cmd As New System.Data.SqlClient.SqlCommand cmd.CommandTimeout = 60 Is there a way to specify a different default value, such that all new command objects will automatically have this value within your solution when they are created? 回答1: As far as I know no, there is no way to change this default. The constructor code for a SqlCommand is this:

问题 everyone I am a student and new to .NET and specially MVC3 development but for one of my project I’ve to work over it and so going through the learning phase Issue and confusion I am facing is regarding DB-Connectivity, whast I leanree d regarding retrieving records from a database is something like this: //Method One: var conn = new SqlConnection(conString.ConnectionString); const string cmdString = "Select * FROM table"; var cmd = new SqlCommand(cmdString, conn); var mySqlDataAdapter = new

问题 I'm working with a DAL object that is written in a layout similar to the following code. I simplified a lot of the code code just to show the setup. public class UserDatabase : IDisposable { private SqlDataAdapter UserDbAdapter; private SqlCommand UserSelectCommand; private SqlCommand UserInsertCommand; private SqlCommand UserUpdateCommand; private SqlCommand UserDeleteCommand; private System.Data.SqlClient.SqlConnection SQLConnection; public UserDatabase() { this.SQLConnection = new System