Question

I have an issue where I need to ONLY get a few things from my initial table, and then join another item from another table, and then join one more item from another table. I thought this would be easy, but it is far from it. Here’s my SQL information (kept it to one record for simplicity).

select * from customers limit 1 \G;
*************************** 1. row ***************************
           CustomerID: 9
       CustomerMapsco: 459
       CustomerActive: 1
    CustomerFirstName: John
     CustomerLastName: Doe
CustomerServiceStreet: 1314 Road Rd.
  CustomerServiceCity: City
 CustomerServiceState: TX
   CustomerServiceZip: 12345
CustomerBillingStreet: 1314 Road Rd.
  CustomerBillingCity: City
 CustomerBillingState: TX
   CustomerBillingZip: 12345
    CustomerHomePhone: 1231231234
    CustomerCellPhone: 1231231234
    CustomerWorkPhone: 1231231234
      CustomerWorkExt: 12345
          CustomerFax: 1231231324
        CustomerEmail: [e-mail]
          CustomerDog: 0
               CrewID: 1
           ScheduleID: 1
            protected: 1


mysql> select * from customerservice limit 1 \G;
*************************** 1. row ***************************
       CustomerSvcID: 15
          CustomerID: 9
       ServiceTypeID: 1
     FrequencyTypeID: 1
               DayID: 5
     CustomerSvcCost: 21
CustomerSvcBeginDate: 2007-01-01 00:00:00
  CustomerSvcEndDate: NULL
1 row in set (0.00 sec)

mysql> select * from frequency
    -> ;
+-----------------+---------------+
| FrequencyTypeID | FrequencyType |
+-----------------+---------------+
|               1 | Weekly        |
|               2 | Biweekly      |
|               3 | One Time      |
+-----------------+---------------+

What I need is the following columns:

customers.CustomerID, customers.CustomerActive, customers.protected, frequency.FrequencyType

I figured I’d have to do a triple join to get the FrequencyType from the customerservice table as they only referenced in that table, rather than the customer table. So therefore, I have to take one extra step to get that information (customers <> customerservice <> frequency).

Answer 1

You are right, you need to join all the three tables to get that information, this should be enough:

SELECT c.CustomerID, c.CustomerActive, c.protected, f.FrequencyType
FROM customers c
   JOIN customerservice s
      ON c.CustomerID = s.CustomerID
   JOIN frequency f
      ON s.FrequencyTypeID = f.FrequencyTypeID