Check if a SQL table exists

Question

What\'s the best way to check if a table exists in a Sql database in a database independant way?

I came up with:

   bool exists;
   const string sql         


        

Answer 1

I fully support Frederik Gheysels answer. If you have to support multiple database systems, you should implement your code against an abstract interface with specific implementations per database system. There are many more examples of incompatible syntax than just checking for an existing table (e.g.: limiting the query to a certain number of rows).

But if you really have to perform the check using the exception handling from your example, you should use the following query that is more efficient than a COUNT(*) because the database has no actual selection work to do:

SELECT 1 FROM my_table WHERE 1=2

Answer 2

If you want to avoid try-catch solutions, I'm suggesting this method, using sys.tables

private bool IsTableExisting(string table)
    {
        string command = $"select * from sys.tables";
        using (SqlConnection con = new SqlConnection(Constr))
        using (SqlCommand com = new SqlCommand(command, con))
        {
            SqlDataReader reader = com.ExecuteReader();
            while (reader.Read())
            {
                if (reader.GetString(0).ToLower() == table.ToLower())
                    return true;
            }
            reader.Close();
        }
        return false;
    }

Answer 3

I don't think that there exists one generic way that works for all Databases, since this is something very specific that depends on how the DB is built.

But, why do you want to do this using a specific query ? Can't you abstract the implementation away from what you want to do ? I mean: why not create a generic interface, which has among others, a method called 'TableExists( string tablename )' for instance. Then, for each DBMS that you want to support , you create a class which implements this interface, and in the TableExists method, you write specific logic for this DBMS.
The SQLServer implementation will then contain a query which queries sysobjects.

In your application, you can have a factory class which creates the correct implementation for a given context, and then you just call the TableExists method.

For instance:

IMyInterface foo = MyFactory.CreateMyInterface (SupportedDbms.SqlServer);

if( foo.TableExists ("mytable") )
...

I think this is how I should do it.