Write queries for substring in a given string

Hello friends, I wish to read the data from an excel file and choose write queries to select tuples for a particular month/year.

 [a,b]= xlsread(fileName,'C:C');

I used this to store all dates in b(in 'dd-mm-yyyy' format). Now I want to display dates for a particular month,say,January i.e mm-01-yyyy

How to I write conditions to check substring of a string stored in b?

Also,please tell me how to I treat them as numbers,as in,if I want to select dates between January and April,what condition should I write.

Thanks.