Two tables with similar columns but different primary keys - mysql

Question

I have two tables from two different databases, and both contain lastName and firstName columns. I need to create JOINa relationship between the two. The lastName columns match about 80% of the time, while the firstName columns match only about 20% of the time. And each table has totally different personID primary keys.
Generally speaking, what would be some "best practices" and/or tips to use when I add a foreign key to one of the tables? Since I have about 4,000 distinct persons, any labor-saving tips would be greatly appreciated.
Sample mismatched data:
db1.table1_____________________ db2.table2_____________________
23 Williams Fritz 98 Williams Frederick
25 Wilson-Smith James 12 Smith James Wilson
26 Winston Trudy 73 Winston Gertrude
Keep in mind: sometimes they match exactly, often they don't, and sometimes two different people will have the same first/last name.

Answer 1

You can join on multiple fields.
select *
from table1
inner join table2
on table1.firstName = table2.firstName
and table1.lastName = table2.lastName
From this you can determine how many 'duplicate' firstname / last name combos there are.
select table1.firstName, table2.lastName, count(*)
from table1
inner join table2
on table1.firstName = table2.firstName
and table1.lastName = table2.lastName
group by table1.firstName, table2.lastName
having count(*) > 1
Conversely, you can also determine the ones which match identically, and only once:
select table1.firstName, table2.lastName
from table1
inner join table2
on table1.firstName = table2.firstName
and table1.lastName = table2.lastName
group by table1.firstName, table2.lastName
having count(*) = 1
And this last query could be the basis for performing the bulk of your foreign key updates.
For those names that match more than once between the tables, they'll likely need some sort of manual intervention, unless there are other fields in the table that can be used to differentiate them?