While working on a Web application that required some page to report data aggregated on several levels of time period – by month, quarter or year – I ran into a very handy way to use the TRUNC function. I was not aware of this usage until now – and since I make it a point to encourage my colleagues to write a blog article on anything new they uncover – no matter how trivial it may seem or how strong the feeling that surely everyone already knows about that – I must play by my own rules and tell you about it.

The challenge I was facing can easily be translated into this question: write a SQL query that reports on the number of employees hired per month (or quarter or year). In fact, use a bind parameter that drives the aggregation level – i.e. the Month, Quarter or Year.

Taking the well known EMP table as the target system, this challenge means that all employees hired in the same Month (or Quarter or Year) should be aggregated in the same group. That in turn means that the aggregation should take place by the MONTH (or QUARTER or YEAR) component of their HIREDATE. Instead of fiddling with TO_CHAR using different date identifiers (which also have been an option) it turns out to be More >