Calculate difference between dates and change status

I will not answer you how to do this in the Database, I will propose a way that (in my opinion) is more appropriate for calculated values. Where these calculated fields would not be fields saved in the database but calculated based on their indicators.

Advantage:

• The field will be recalculated at each new request, based on the current state of the object;
• You do not need Procedures, Functions, or Triggers for this task linked to the database;
• You do not run the risk of the calculated field being out of date based on your indicators;
• Among other numerous small advantages that you can easily point out;

Disadvantages:

• If the bank is used by more than one system, all those involved will have to enter the rule to calculate the calculated fields;
• If you do not use a Class template (Assign the query cursor directly to the DataSource (particularly I do not recommend));

Implementation

It would be something similar to this in C # (which seems to be the language you're using):

public class Calibragem{
    public long Id { get; set; }
    public DateTime Data { get; set; }
    public DateTime Vencimento { get; set; }
    public StatusCalibragem Status { 
        get{
            // aqui você faz a conta da diferença em mémoria
            /** 
             * DUVIDA: aqui você não deveria calcula a Data da ultima calibragem com a 
             * data atual(DateTime.Now) ou o Vencimento com a data atual(DateTime.Now),
             * ao invés de fazer o calculo entre as duas Datas?
            **/    
            TimeSpan diff = Data - Vencimento;

            // verifica a diferença em dias para ver qual o status atual
            if(diff.Days > 30){
                return StatusCalibragem.EmDia;
            }
            if(diff.Days < 30){
                return StatusCalibragem.Calibrar;
            }
            // não entendi quando será Vencida, com sua explicação
        } 
        private set; 
    }
}

public enum StatusCalibragem
{
    EmDia,
    Calibrar,
    Vencida
}

In the database your table would only have the columns:

ID | DATA_CALIBRAGEM | VENCIMENTO_CALIBRAGEM

To update the column according to the date conditions you can use something like this:

UPDATE suatabela
   SET status = CASE WHEN CURDATE > data_vencimento THEN
                   status1
                ELSE
                   CASE WHEN DATEDIFF(CURDATE(), data_calibragem) > 30 THEN
                      status2
                   ELSE
                      status3
                   END   
                END;

Remembering that with this statement all records in the table will be affected. Because at some point, each one will be in one of the three situations you mentioned.

Comments:

• CURDATE returns the current day ( link ).
• DATEDIFF returns the difference between two dates ( link ).

For this statement to be run daily you must create an event in the database ( link ).

An example:

delimiter |

CREATE EVENT e_upd_calibragem
    ON SCHEDULE
      EVERY 1 DAY
    COMMENT 'Atualiza status de calibragem'
    DO
      BEGIN

        UPDATE suatabela
           SET status = CASE WHEN CURDATE > data_vencimento THEN
                           status1
                        ELSE
                           CASE WHEN DATEDIFF(CURDATE(), data_calibragem) > 30 THEN
                              status2
                           ELSE
                              status3
                           END   
                        END;

      END |

delimiter ;