检查数据库中是否存在行，并返回布尔值

Question

I have this funcion that takes a name and check in a database if a row exists with that name. However, i dont know how to determine if the row exists or not.

My code right now is

public static boolean rowExists(String player) throws SQLException {
    String sql = "SELECT EXISTS(SELECT * FROM currency WHERE name='"+player+"');";
    Bukkit.broadcastMessage(player);
    Statement stmt = con.createStatement();
    
    ResultSet up = stmt.executeQuery(sql);
    boolean nut = up.next();
    Bukkit.broadcastMessage("nut: " + nut + "  ");

    return nut;
}

nut is the boolean where true is the entry exists, and false it does not. Currently nut always returns as true, whether the row exists or not.

Answer 1

Simple queries are better:

SELECT 1 FROM currency WHERE name=%s LIMIT 1

This will return a single row of 1 if it exists, an 0 rows if it doesn't exist.

Also use prepared statement to avoid SQL injection.