Will flat file database work with relation between two columns?

Will flat file database work with relation between two columns?

Database.txt
Field1-Field2
Field3-Field4
Field1-Field2
Field1-Field2
[Saved the above data into a txt file from a html form]
**www.site.com/?type=Field1** should output **Field2**
**www.site.com/?type=Field3** should output **Field4**
....... and so on
I want to check all the Field1's for the type and if it is found, I want
to display Field2. What would be the best way to store data for this need?
How do I check the first column for a string and display it's
corresponding string? All in PHP.