We're building a small-sized GIS Web application (as a school project) right now.
In terms of spatial database support and capabilities, which is better?
Check it out for yourself, you know what you're looking for in your GIS-application: http://www.bostongis.com/PrinterFriendly.aspx?content_name=sqlserver2008_postgis_mysql_compare
In general PostGIS is much more mature and is very flexible. You can create any function, operator, index type or what so ever. It has (almost) no limits.
You're doing a school project for a company. The company is already established and have selected the technologies. Instead of trying to change their minds (a highly unlikely uphill battle at best), you should use what they have already invested in and consider it a learning opportunity. It doesn't matter what you think is better... they've already decided MySQL is better. Welcome to the "real world". It's not the answer you were looking for, but a fact of life. :-/
Postgis+PostgreSQL is much better than mysql. mysql supports datatypes of spatial database but there are no/limited spatial functions. postgis offers you lots of functions which will help you and will make your task easier.
来源：https://stackoverflow.com/questions/3343022/mysql-vs-postgres-postgis-spatial-database-support