How can I get a total value from the same column of multiple rows in a mysql query?

Question

I have a project in ASP.Net (C#) connected to a game database. I have a player table and I want to get the total value of the playtime row from all the players with the same account_id . My last logic was this:

MySql.Data.MySqlClient.MySqlConnection conn;
MySql.Data.MySqlClient.MySqlCommand cmd;
String queryStr;
String connStringPlayer = System.Configuration.ConfigurationManager.ConnectionStrings["PlayerDB"].ToString();
conn = new MySql.Data.MySqlClient.MySqlConnection(connStringPlayer);
conn.Open();
queryStr = "SELECT playtime FROM player.player WHERE account_id='" + AccountId + "' LIMIT 5";
cmd = new MySql.Data.MySqlClient.MySqlCommand(queryStr, conn);
{
    Int32 countpt = (Int32)cmd.ExecuteScalar();
    String playcount = countpt.ToString();
    AccountInfoTotalGameMinuetsValue.Text = playcount;
}
conn.Close();

In this way my AccountInfoTotalGameMinuetsValue Label displays only the playtime of the 1st player of this account_id (2 players exist in this account).

Answer 1

SUM is what you are looking for

SUM([DISTINCT] expr)

Returns the sum of expr. If the return set has no rows, SUM() returns NULL. The DISTINCT keyword can be used to sum only the distinct values of expr.

SUM() returns NULL if there were no matching rows.

So the following query Will give you the totals for all the players

SELECT account_id, SUM(playtime) FROM player.player GROUP BY account_id;

if you want the information for just one player

SELECT account_id, SUM(playtime) FROM player.player 
WHERE account_id = some_id 
GROUP BY account_id;