1. A computer program product, the computer program product comprising a computer readable storage medium having program code embodied therewith, the program code executable by at least one processor to perform: performing a prior compare operation by: receiving an input vector for each of one or more attributes of input data that represent one of a partition-by column and an order-by column in a database query; generating a per-attribute comparison vector for each input vector; and producing a single output vector using each per-attribute comparison vector, wherein each value of the single output vector is a Boolean attribute whose value for a given tuple is true if a current value and a most recent prior value of any of the one or more attributes are different; and in response to receiving a second database query with multiple On-line Analytical Processing (OLAP) functions that each have different partitioning and ordering specifications and that share a sort, identifying a minimal set of prior compare building blocks with a minimal number of scans over the input data for use by the multiple OLAP functions; and computing remaining prior compare functions using the minimal set of the prior compare building blocks.