从MySQL结果中分配BOOL

Question

我正在攻击我的第一个ruby脚本来读取和写入mysql。

我想知道某条记录是否存在。我试过了：

sql = "SELECT EXISTS(SELECT * FROM UserTrucks WHERE User = ? AND Truck = ?)"
pst = con.prepare(sql)
does_exist = pst.execute(user_id, truck_id)

但是当我打印should_alert类时，它是一个MySQL :: STMT而不是True或False类，甚至是0/1。

我在这里缺少什么？准备好的陈述是否适合用于此目的？

Answer 1

sql = "SELECT IF( EXISTS(SELECT * FROM UserTrucks WHERE User = ? AND Truck = ?), 1, 0)"

Answer 2

为什么不使用计数

sql = "SELECT CASE WHEN COUNT(1) > 0 THEN 1 ELSE 0 END AS Exist FROM UserTrucks WHERE User = ? AND Truck = ?"

或

sql = "SELECT CASE WHEN EXISTS(SELECT * FROM UserTrucks WHERE User = ? AND Truck = ?) THEN 1 ELSE 0 END AS Exist"