Select Query with Where condition depending on lis

问题:

I've an sql table. I've also a list in my Asp.Net code (C#).

public static List listColumns = new List();

And listColumns contains 1,2,3...10 randomly. For example it can contains 1, 5, 6, 9. I want to make a query with this conditions. So, If the list has these values, my query should be:

SELECT * FROM Table WHERE id=1 or id=5 or id=6 or id=9

The listColumns may contains different values and has different counts. How can I do this query regularly?

回答1:

Here is a solution without a for loop, but unfortunately also without a parameterized SQL statement:

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;

public class test {
  public static void Main(string[] args)
  {
    //List<int> listColumns = new List<int>(){ 1, 5, 6, 9};
    System.Collections.Generic.List<int> listColumns = new System.Collections.Generic.List<int>(){ 1, 5, 6, 9};
    string s = String.Join(", ", listColumns.Select(x => x.ToString()));

    string sql = String.Format("SELECT * FROM Table WHERE ID IN ({0})", s);
    Console.WriteLine(sql);
  }
}

Please note that using select * is considered as a bad practice

edit Here is some new code because your list is of type System.Web.UI.MobileControls.List

string sql = String.Format("SELECT * FROM Table WHERE ID IN ({0})", 
                 listColumns.ListItem.Value);

edit 2 I have taken the code from your comment:

list.Items.Clear(); 
string values = DropDownList4.SelectedValue; 
string[] words = values.Split(','); 

foreach (string s in words) 
    if (s != "" && s != string.Empty && s != null)     
        list.Items.Add(s);

I guess that you have this on the dropdown changed event or something? and your dropdown has a string like "1,5,6,9" in the value. If all my assumptions are correct you can use:

System.Collections.Generic.List<int> selectedValues = new     System.Collections.Generic.List<int>();

foreach (string s in words)
    if (!String.IsNullOrWhiteSpace(s))
        selectedValues.Add(Convert.ToInt32(s));
string ids = String.Join(", ", selectedValues.Select(x => x.ToString()));
string sql = String.Format("SELECT * FROM Table WHERE ID IN ({0})", ids);

回答2:

//assume input is List of integers 
List<int> ids = new List<int> { 1,5,6,9 };
//build your SQL statement as below
string cmdText = "SELECT * FROM Table  WHERE id IN ({0})";
// add parameters for each id value 
string[] paramNames = ids.Select(
    (s, i) => "@id" + i.ToString()
).ToArray();

string inClause = string.Join(",", paramNames);
//set the parameter values
using (SqlCommand cmd = new SqlCommand(string.Format(cmdText, inClause))) {
    for(int i = 0; i < ids.Count; i++) {
       cmd.Parameters.AddWithValue(paramNames[i], ids[i]);
    }
}

回答3:

 //assume a list of int value name listColumns
  var listColumns = new List<int>() { 1, 5, 9 };
  var sb = new StringBuilder();
  sb.Append("SELECT * FROM Table");

   for (int i = 0; i < listColumns.Count; i++)
   {
       if (i == 0)
          {
             sb.Append(" where ");
             sb.Append(" id=" + listColumns[i]);
          }
        else
             sb.Append(" or id=" + listColumns[i]);
    }
   Console.Write(sb.ToString());

pass query variable to sqlcommand

回答4:

Linq-to-SQL:

var listColumns = new List<int>() { 1, 5, 6, 9 };
db.Table.Where(x => listColumns.Distinct().Contains(x.id)).ToString();

Generated SQL:

SELECT
    [Extent1].[id] AS [id],
FROM [Table] AS [Extent1]
WHERE [Extent1].[id] IN (1, 5, 6, 9)

EDIT

An approach that yields parameterized SQL (not that it's all that useful if the number of parameters keeps changing):

listColumns.Distinct().Aggregate(db.Table, (current, c) => current.Where(x => c == x.id)).ToString();