Functions return information from the database.
Aggregate data (for example, AVG, COUNT, MAX, MIN, SUM, STDDEV, VARIANCE)
Manipulate numeric data (for example, ABS, CEILING, SQRT, TRUNCATE)
Manipulate string data (for example, LENGTH, SOUNDEX, UCASE)
Manipulate date and time data (for example, TODAY, DATEDIFF, DATEPART, MINUTES)
Convert retrieved data from one format to another (CAST, CONVERT)
Manipulate analytical data (for example, DENSE_RANK, NTILE, PERCENT_RANK, PERCENTILE_CONT, PERCENTILE_DISC, RANK)