问从c#中的字符串中删除最后两个或多个单词

EN

  string[] selects = new string[] {
    "select 'abc','xyz','123'",
    "select 'def','pqr','456'", 
  };

  // select 'abc','xyz','123' Union all select 'def','pqr','456' 
  string finalQuery = string.Join(" Union all ", selects);

  string finalQuery = myString.EndsWith("Union all") 
    ? myString.Substring(0, myString.Length - "Union all".Length)
    : myString;

   private IEnumerable<string> MySelects() {
     foreach(var item in obj) {
       // Some Logic Here...

       // When you are ready to create a select just "yield return" it and keep looping
       yield return $" SELECT '{item.a}', '{item.b}', '{item.c}'";

       // Some Other Logic Here...
     } 
   }

   string finalQuery = string.Join(" Union all ", MySelects());

   StringBuilder sb = new StringBuilder();

   foreach(var item in obj) {
     // if we have a query, next one should be add via "UNION ALL"
     if (sb.Length > 0)
       sb.Append(" UNION ALL ");

     sb.Append($"SELECT '{item.a}', '{item.b}', '{item.c}'");
   }

   string finalQuery = sb.ToString();

string input = "select 'abc','xyz','123' Union all select 'def','wer','456' Union all";

string result = string.Join(" ", input.Split(' ').Reverse().Skip(2).Reverse());

var toRemove = "Union all";
if (yourString.EndWith(toRemove ))
{
  yourString = yourString.SubString(0, yourString.Length - toRemove.Length).Trim();
}