Database Design with Change History

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One way is to have a MyTableNameHistory for every table in your database, and make its schema identical to the schema of table MyTableName, except that the Primary Key of the History table has one additional column named effectiveUtc as a DateTime. For example, if you have a table named Employee,

Create Table Employee
{
  employeeId integer Primary Key Not Null,
  firstName varChar(20) null,
  lastName varChar(30) Not null,
  HireDate smallDateTime null,
  DepartmentId integer null
}

Then the History table would be

Create Table EmployeeHistory
{
  employeeId integer Not Null,
  effectiveUtc DateTime Not Null,
  firstName varChar(20) null,
  lastName varChar(30) Not null,
  HireDate smallDateTime null,
  DepartmentId integer null,
  Primary Key (employeeId , effectiveUtc)
}

Then, you can put a trigger on Employee table, so that every time you insert, update, or delete anything in the Employee table, a new record is inserted into the EmployeeHistory table with the exact same values for all the regular fields, and current UTC datetime in the effectiveUtc column.

Then to find the values at any point in the past, you just select the record from the history table whose effectiveUtc value is the highest value prior to the asOf datetime you want the value as of.

 Select * from EmployeeHistory h
 Where EmployeeId = @EmployeeId
   And effectiveUtc =
    (Select Max(effectiveUtc)
     From EmployeeHistory 
     Where EmployeeId = h.EmployeeId
        And effcetiveUtc < @AsOfUtcDate)

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