Computed columns

No coding an no parameter is necessary in 2 cases (most common cases):

1/ text 1 to 1 relationship, get the department of an item (type A)

2/ coefficient 1 to 1 relationship, get price from qty using item price (type B)

SB needs 2 functions per computed column

1/ <comp_col_name>_before

2/ <comp_col_name>

See input/output of these functions in common.h

By default real column has priority over a computed column with same name

New_customer_id is a computed text column

Its destination col_type is t_customer_id

We are going to return always the same value

So we don't need other columns to compute new_customer_id in this basic case

Please note that needed_col_count can't be zero, because on the in/out value at first position

Hence needed_col_names=["dept"]

select_context_type A

select_context_type B

New_customer_id will be equal to the first customer_id will have 2 values:

1/ current customer_id if item_id is artA (ival=10)

2/ null otherwise

Dept was here for clarity (in/out value), let's remove it, and use customer_id instead

And we won't need to update the new in/out in case 1/ because it is already good

A context is a C custom objects stored in memory be SB ant that can be used by other part of your custom C code

Some predefined contexts for most common operations are provided (see common.h)

Sometimes your computed column will need other information because the needed columns in not enough

Context should be used in that case

Sometimes predefined context is not enough, or you needed several custom contexts

In such cas you should define your own context

Index can be used if there is only one needed column and that this column has an index (is part of a dimension)