从C＃中的字符串中删除最后两个或多个单词

Question

I have string likely

select 'abc','xyz','123' Union all select 'def','wer','456' Union all

the string is generated by loop eg

foreach(var item in obj)
{
  " SELECT'" + item.a + "'," + item.b + ," + item.c + "UNION ALL";
}

Now i want to remove the "Union all" written in the last of the string.How can i do this is single OR using regex in C# .IndexOf wont work as i have multiple "Union all" in my string .

Answer 1

As far as I can see, you are trying to build finalQuery from several select s; you can do it with a help of Join :

  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);

If you, however, want to remove the very last Union all if it is, you can test the string with EndsWith :

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

Edit: If you generate your selects in a loop (see comments below), you can try extracting method turning loop into IEnumerable<String> :

   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...
     } 
   }

and then again Join :

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

Finally, if you want to stick to loop (for whatever reason), add if :

   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();

Answer 2

You can combine string.Join and LINQ Skip :

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

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

DEMO HERE

Answer 3

I would start with somelink like this. In case your replacement gets more complicated you can start using regular expressions.

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

PS Get the toRemove string from some logical location and don't use it in your procedure like this to avoid using magic values..

Answer 4

You can use this as a function;

var toRemove = "Union all";

if (string.IsNullOrWhiteSpace(yourString))
return;

var pos = yourString.LastIndexOf(stringToFind);

 if (pos < 0) return;

string newString = yourString.Remove(pos, yourString.Length);

return newString;