SQL Functions
Oracle SQL has three main types of functions: single-row functions, user-defined functions, and aggregate functions. Single-row functions are usually referred to simply as functions and are the type we will be describing here. User-defined functions are functions that we write ourselves, using either Java or PL/SQL, and can be used like regular SQL functions; we will examine those in Chapter 5, “PL/SQL.” Aggregate functions are a special kind of function that combines multiple values returned by a query that returns multiple rows of data—to calculate a total or an average, for example. Aggregate functions will be examined in the next chapter, “More SQL: Queries, Subqueries, and Views.”
Single-row functions are similar to Java methods: ...
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