Question

假设我有一个带有名为$fighter1 = $_POST["fighter1"]; $fighter2 = $_POST["fighter2"]; $fighter3 = $_POST["fighter3"]; $fighter4 = $_POST["fighter4"]; $fighter5 = $_POST["fighter5"]; /********************** CONNECTION ***********************/ $conn = new mysqli($servername, $username, $password, $dbname); if ($conn->connect_error) { die("Connection Failed: " . $conn->connect_error);} /************************ UPDATES ************************/ if ($fighter1 == "Conor McGregor") { $sql = "UPDATE Predictions_Poll SET fighter_one_votes = fighter_one_votes + 1 WHERE id = 1"; } else if ($fighter1 == "Khabib Nurmagomedov") { $sql = "UPDATE Predictions_Poll SET fighter_two_votes = fighter_two_votes + 1 WHERE id = 1"; } if ($fighter2 == "Georges St‑Pierre") { $sql = "UPDATE Predictions_Poll SET fighter_one_votes = fighter_one_votes + 1 WHERE id = 2"; } else if ($fighter2 =="Tyron Woodley") { $sql = "UPDATE Predictions_Poll SET fighter_two_votes = fighter_two_votes + 1 WHERE id = 2";} if ($fighter3 == "Israel Adesanya") { $sql = "UPDATE Predictions_Poll SET fighter_one_votes = fighter_one_votes + 1 WHERE id = 3"; } else if ($fighter3 =="Kelvin Gastelum") { $sql = "UPDATE Predictions_Poll SET fighter_two_votes = fighter_two_votes + 1 WHERE id = 3"; } if ($fighter4== "Francis Ngannou") { $sql = "UPDATE Predictions_Poll SET fighter_one_votes = fighter_one_votes + 1 WHERE id = 4"; } else if ($fighter4 == "Brock Lesnar") { $sql = "UPDATE Predictions_Poll SET fighter_two_votes = fighter_two_votes + 1 WHERE id = 4"; } if ($fighter5 == "Nate Diaz") { $sql ="UPDATE Predictions_Poll SET fighter_one_votes = fighter_one_votes + 1 WHERE id = 5"; } else if ($fighter5 == "Tony Ferguson") { $sql = "UPDATE Predictions_Poll SET fighter_two_votes = fighter_two_votes + 1 WHERE id = 5"; } /****************** UPDATE SUCCESS CHECK *******************/ if($conn->query($sql)== true) {echo "Record Successfully Updated";} else {echo "Error Updating Record: " . $conn->error;} $conn->close(); ?>的属性的对象列表，我试图结合这些值来为查询创建一个片段，例如：

Id

问题是我得到：UNION ALL SELECT 30 UNION ALL SELECT 31 UNION ALL SELECT ...

老实说，我找不到直接从30 UNION ALL SELECT 31 UNION ALL SELECT获取它的方法，这是我的实现：

string.JOIN

Answer 1

string.Concat(teams.Skip(1).Select(c => " UNION ALL SELECT " + c.Id));

或避免使用空格：

string.Join(" ", teams.Skip(1).Select(c => "UNION ALL SELECT " + c.Id));

Answer 2

您可以使用linq。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

public class Program
{
    public static void Main()
    {
        var values = new List<int> { 1, 2, 3, 4 };
        var str = values
            .Select(i => $"UNION ALL SELECT {i} ")
            .Aggregate(new StringBuilder(), (sb, a) => sb.Append(a), s => s.ToString());
        Console.WriteLine(str);
    }
}

C# fiddle

如何在每个元素之前添加string.Join分隔符

2 个答案: