MySQL SELECT and SORT performance - v. large table
As mentioned in comments (it is really answer for original question) - using function in WHERE - prevent any indexes using.

First of all, You can check - how many of Your queries use form 

SELECT * FROM


this is really bad practice with applications, exactly because - if You add new column, some of Your code could be broken. For example:

INSERT into table2 SELECT * FROM table1


If You can fix this (or You not have problems code), You can:


convert IncorporationDate to Date format and use this column 
or easy add 1 more column with proper Date type and use it in queries


But first - You must be sure, all other code will not be broken by new column.

Then You can use one of the tools from answer for Your other question:


Talend - http://www.talend.com
StreamSets - http://www.streamsets.com
Apache NiFi - https://nifi.apache.org,
https://hortonworks.com/apache/nifi/


now much more similar tools present on market, many of them free in parts cover 99% of life cases. 
And ETL it more often solution rather than work with build functions only.


Clean
Transform
Load


For answer about next potential question - what with speed?
we load tables from 4M to 40M between instances - MySQL, MS SQL, Redshift
For "small" we use direct insert from ETL tools, for Big - prepare clean file for load, than direct load (Redshift from S3)

Just add live example - "how it could work"

One of Our scripts - run series of queries with search target records by substring from 2 columns + other parameters. 
Changing the structure also not possible by the same reasons - a lot of place where need to make changes and no free developers resources. 2 table 3M rows per month.


Original time - 7.5 Hours
Modified process - prepare with Talend tables for past month with all optimised structure. 
modification only this script - for exclude substrings from SELECT query, do not touch any other in system. SELECT from prepared tables, write result to same as in original.


Prepare - 5m, script execution - 12m, total time of whole process - 17minutes.