Matrices in SQL
Arrays are not the same thing as matrices. An array is a data structure whose elements are accessed by a numeric value called an index. A matrix is an array with mathematical operations defined on it. A matrix can be one, two, three, or more dimensional structures. The most common mathematical convention has been to use the letters i, j, and k for the indexes.
SQL had neither arrays nor matrices because the only data structure in the Relational Model is a table. Arrays violate the rules of First Normal Form (1NF) required for a relational database, which say that all columns are scalars.
This was unfortunately changed in SQL:2003 with the addition of collection types. You can now declare a column to be an array of one of the ...