sql server - How to implement this data structure in SQL tables -


i have problem can summarized follow:

assume implementing employee database. each person depends on position, different fields should filled. example if employee software engineer, have following columns:

name family language technology candevelopweb

and if employee business manager have following columns:

name family fieldofexpertise maximumcontractvalue bonusrate

and if employee salesperson other columns , on.

how can implement in database schema?

one way thought have related tables:

coretable:

name family type

and if type 1 employee software developer , hence remaining information should in table softwaredeveloper:

language technology candevelopweb

for business managers have table columns:

fieldofexpertise maximumcontractvalue bonusrate

the problem structure not sure how make relationship between tables, 1 table has relationship several tables on 1 column.

how enforce relational integrity?

there few schools of thought here.

(1) store nullable columns in single table , populate relevant ones (check constraints can enforce integrity here). people don't because afraid of nulls.

(2) multi-table design each type gets own table. tougher enforce dri trivial application or trigger logic.

the problem either of those, add new property (like canreadupsidedown), have make schema changes accommodate - in (1) need add new column , new constraint, in (2) need add new table if represents new "type" of employee.

(3) eav, have single table stores property name , value pairs. have less control on data integrity here, can constraint property names strings. wrote here: http://sqlblog.com/blogs/aaron_bertrand/archive/2009/11/19/what-is-so-bad-about-eav-anyway.aspx


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