How to check empty table in Where Condition

I want to update several columns of a table at the same time. And the value for each column is retrieved from several tables. My tables are:

Table : Customer
Columns are:
customerCode
kategori
design
designCode
value

Table Name : Customer_kategori 
Columns:

customerCode
kategori

and similar .....

My sql query is:

UPDATE Customer
SET 
    kategori = Customer_kategori.kategori,
    design = Customer_design.design,
    designCode = Customer_designCode.designCode,
    value = Customer_value.value

FROM 
     Customer_kategori,
     Customer_design,
     Customer_designCode,
     Customer_value
WHERE
     Customer_kategori.customerCode = Customer.customerCode
     AND Customer_design.customerCode = Customer.customerCode
     AND Customer_designCode.customerCode = Customer.customerCode
     AND Customer_value.customerCode = Customer.customerCode

The columns are updated if all the tables (Customer_kategori, Customer_design, Customer_designCode, Customer_value) contains values. But if tables ar开发者_JAVA百科e empty, columns are not updated as Where condition is not satisfied.

I also try using CASE in WHERE Condition. My code is ,

WHERE
        Customer_kategori.customerCode = CASE WHEN Customer_kategori.customerCoder IS NOT NULL THEN Customer.customerCode END
        AND Customer_design.customerCode = CASE WHEN Customer_design.customerCode  IS NOT NULL THEN  Customer.customerCode  END
        AND Customer_designCode.customerCode = CASE WHEN Customer_designCode.customerCode  IS NOT NULL THEN  Customer.customerCode  END
        AND  AND Customer_value.customerCode =   CASE WHEN Customer_value.customerCode  IS NOT NULL THEN  Customer.customerCode  END

But this does not work either. I also try to check the table, with following where clause,

WHERE
    CASE WHEN (select count(Customer_kategori.customerCode) > 0 from Customer_kategori) THEN Customer_kategori.customerCode = Customer.customerCode END

But no success..

In short:

1. I want to check if tables are empty in WHERE clause
2. And if it is empty I just want to ignore checking columns of those table that are empty.

Or may be there is other better way .... Any suggestion is appreciated...

Thank you

Will this work?

WHERE
(
    Customer_kategori.customerCode = Customer.customerCode
    OR 
    0 = (select count(Customer_kategori.customerCode) from Customer_kategori)
)
AND
(
    ....
)

UPDATE

How about this:

UPDATE Customer
SET 
    kategori = Customer_kategori.kategori,
    design = Customer_design.design,
    designCode = Customer_designCode.designCode,
    value = Customer_value.value

FROM 
     Customer left join Customer_kategori on Customer_kategori.customerCode = Customer.customerCode 
     left join Customer_design on Customer_design.customerCode = Customer.customerCode 
     left join Customer_designCode on Customer_designCode.customerCode = Customer.customerCode 
     left join Customer_value on Customer_value.customerCode = Customer.customerCode