Publisher Summary This chapter discusses the features defined by Structured Query Language/Online Analytical Processing (SQL/OLAP), including both the underlying concepts and the actual SQL syntax used to accomplish the goals meant to be satisfied by the standard. The most fundamental enhancement that SQL/OLAP adds to the SQL language is the notion of a window—a user-specified selection of rows within a query (or a logical partition of a query) that determines the set of rows used to perform certain calculations with respect to the current row under examination. In SQL/OLAP, window sizes can be specified in terms of individual rows (e.g., one can specify that a window extends for four rows on either side of the current row), or it can be specified that a window extends to all rows on either side of the current row in which the value of some column is within a certain range of the value of that column in the current row. SQL/OLAP windows have three essential aspects: window partitioning, window ordering, and window framing. Each of these aspects has a significant impact on the specific rows of data visible in a window at any point in time.