A relational database is designed to enforce the uniqueness of primary keys by allowing only one row with a given primary key value in a table. A foreign key is a column or a set of columns in a table whose values correspond to the values of the primary key in another table.
We can connect a temperature sensor connected to the water and a heater or cooler sensor, we have created a program to check the temperature from the sensor.
when the water is hotter than recommended, we turn on the refrigerator and when it is cold, we turn on the heater
so correct answer is water temperature gauge sensor
