InfluxDB is an open-source time-series database that allows users to store and query large amounts of data across various dimensions, including measurements, tags, and timestamps. To perform cross-measurement math or grouping, all data must be stored under a single measurement, as InfluxDB does not support joins. Users can use the `GROUP BY` clause with the `time()` function to group data by time intervals, but they should be aware of how InfluxDB handles time boundaries and rounding. To specify tag values in the `WHERE` clause, users must enclose them in single quotes. Additionally, when using `GROUP BY time()` queries, users may get results for multiple time intervals due to the default rounded calendar time boundaries, which can be altered by including an offset interval in the query.