How to correctly send the value of a null variable in an INSERT?

Question

Assuming I have the following code:

public async void InsertBanco(string parametro1, string parametro2)
{
    var b = new BancoN();
    SetBanco(b);
    await b.EnviaMySQLInsert($"INSERT INTO tabela(parametro1, parametro2) " +
    $"VALUES('{parametro1}','{parametro2}') ;");
 }

In some situations the parametro2 can be null, how do I send NULL in the insert?

If I call InsertBanco("Teste", null), for example, sql would look like this:

INSERT INTO tabela(parametro1, parametro2) VALUES('Teste','');

What if I send the string with the value "NULL" (InsertBanco("Teste", "NULL")), this string will be inserted into the database, instead of setting the value to null.

But the right thing would be:

INSERT INTO tabela(parametro1, parametro2) VALUES('Teste', NULL);

How can I fix this problem?

---

EDIT

Clarifying the problem: in some cases the parametro2 will be null and in some cases will be a string("Text", for example).

When is a string, the code I have works normally. But when I need to set null in the bank, the way it was written the code will never work...

How to write the method InsertBanco so that it can send the correct sql when the parametro2 is null and void and when string normal??

Answer 1

You can use the query:

INSERT INTO tabela(parametro1, parametro2) VALUES('parametro1', NULLIF ('parametro2', ''));

Answer 2

Test if parametro2 is null and construct the proper insert. Anything like that:

public async void InsertBanco(string parametro1, string parametro2)
{
    var b = new BancoN();
    SetBanco(b);
    if(parametro2 == null)
    {
        await b.EnviaMySQLInsert($"INSERT INTO tabela(parametro1) " +
                                 $"VALUES('{parametro1}') ;");
        return;
    }
    await b.EnviaMySQLInsert($"INSERT INTO tabela(parametro1, parametro2) " +
                             $"VALUES('{parametro1}','{parametro2}') ;");
 }

Answer 3

Use a conditional expression to check if parametro2 is empty or void

await b.EnviaMySQLInsert( $"INSERT INTO tabela(parametro1, parametro2) VALUES('{parametro1}', { ((string.IsNullOrEmpty(parametro2)) ? "NULL" : ("'" + parametro2 + "'") )}); ");

Answer 4

Check whether the parametro2 is empty if you have a pass NULL, otherwise pass the value of parametro2.

await b.EnviaMySQLInsert($"INSERT INTO tabela(parametro1, parametro2) " + 
                         $"VALUES('{parametro1}'," + parametro2 == "" ? "NULL);" : $"'{parametro2}');");