Seems likely that you have a data type issue. What data types does MySQL support? If they only support datetime as opposed to just a date (without time), then you may have no alternative but to use either OPENQUERY or OPENROWSET as part of your overall query. That portion would specify the Linked Server (existing or temporary) and the native MySQL query, which would become a table you could use as part of a T-SQL query that could then CONVERT the relevant column to date as opposed to datetime. However, we don't have any detail here as to exactly how you connect to the MySQL instance, so let us know...
mySQL does support DATETIME but I think it's all about the incompatibility of the mysql syntax using SSRS.
I finally found a way to fix the issue in this grouping of dates. I just managed to create a group expression in my chart report.
under Category Group Properties i added:
=Year(Fields!collecteddate.Value)
=Month(Fields!collecteddate.Value)
=Day(Fields!collecteddate.Value)
🙂
🙂