Add New Field To Existing Table And Populate New Field With Existing Data

-Microsoft Access 2010

-Existing Access Database contains tables with 1-2 million records

I would like to add a field[dol] to an existing table[rei]. I need this new field[rei].[dol] to be populated with existing data from another table[main] based on the associated field[main].[account1] or [main].[account2] or [main].[account3].

Table1[main]
...account1
...account2
...account3
...dol

[code]...

In the [main] table. There is always data in [dol]. But there is NOT always data in the [account] fields. Sometimes there is multiple account numbers per [dol] but not always.

Customers will ALWAYS have at least 1 [account] number and [dol]. Some will have multiple [account] numbers and [dol]. Sometimes these [account] numbers are the same in multiple fields[account1] [account2] [account3].I just need to do a lookup or something to find the [account#] and pull in its [dol] from the [main] table and populate it in [rei].[dol].