Question

i’ve a problem for a table update. follow table structure:

Table1
  tableid
  ...
  ... 
  productID_1
  productID_2
  productID_3

Table2
  productID
  Total

I’ve to totalize each product in table2.

For example:

SELECT COUNT(*) as tot, ProductID_1 FROM Table1 GROUP Table1 

then the UPDATE table2 SET total =..??? (how can i do) WHERE productID_1 = ….

Hope you can help me.

Thank you

Answer 1

Your options in terms of simplifying the query greatly depend on the product and version you are using. However, a solution that should work in most databases would be:

Update Table2
Set Total = (
            Select Count(*)
            From (
                    Select productId_1 As ProductId From Table1
                    Union All Select productId_2 From Table1
                    Union All Select productId_3 From Table1
                    ) As Z
            Where Table2.ProductId = Z.ProductId
            Group By ProductId
            )

A big reason this query is cumbersome is that the data in Table1 is not normalized. Instead you should consider a structure for Table1 like:

Create Table Table1 (
                    TableId <datatype> not null
                    , ProductId <datatype> not null
                    , Constraint PK_Table1 Primary Key ( TableId, ProductId )
                    )