intermediate   

PostgreSQL has aggregate functions called bool_and and bool_or which it's had for as far back as I can remember. What do they do? given rows of premises (things that resolve to booleans), bool_and will return true if all of the premises are true. Similarly bool_or will return true if any of the premises in the set of rows is true. What if however your boolean expressions are not in rows, but instead passed in as a sequence of arbitrary statements of questionable fact. We want a function like bool_or or bool_and that takes an arbitrary number of boolean arguments. Are there functions that fit the bill. Indeed there are, but they don't scream out and say I work with booleans because they fit into a class of function we discussed in The wonders of Any Element and that also happen to be variadic functions. These are none other than greatest and least and they are old timer functions that you can find in most versions of PostgreSQL. We'll demonstrate how to use all 4 with booleans in this article. It must be said that greatest and least are much more useful when applied to other data types like dates and numbers, but we were amused at the parallel with booleans.