PL/SQL collections are data structures that can store multiple values. There are three types of PL/SQL collections: arrays, associative arrays, and nested tables. Arrays are the simplest type of collection. An array is a sequence of elements of the same data type. Associative arrays (also called index-by tables or hash tables) are similar to arrays, except that the index value can be any data type, not just a number. A nested table is like an array, except that it can be stored in a database column and it can be sparse (that is, it can have missing elements).PL/SQL collections are data structures that can hold a variable number of values. They are similar to arrays in other programming languages, but with some important differences. PL/SQL collections can be either index-by tables or nested tables. Index-by tables are similar to arrays, in that they can be accessed by their index (array subscript). However, they have no upper limit on the number of elements they can hold, and their indices do not have to be consecutive integers. Nested tables are similar to one-dimensional arrays, in that each element has a fixed position within the table. However, nested tables can be stored in database columns, and they can be passed as parameters to procedures and functions.PL/SQL collections are data structures that can store multiple values. They are similar to arrays in other programming languages. There are three types of PL/SQL collections: associative arrays, nested tables, and varrays. Associative arrays use keys to index their values, while nested tables and varrays use sequential integers. Collections can be used to store data in a single PL/SQL variable or database column, or they can be used as parameters to procedures and functions.Oracle PL/SQL collections are data structures that can store multiple values. There are three types of collections: varrays, nested tables, and associative arrays. Varray is the simplest type of collection. It can store a fixed-size sequential list of elements. Nested tables and associative arrays are more complex types of collections. They can store an unlimited number of elements and allow indexing by arbitrary keys.