A wide-column database (sometimes referred to as a column database) is similar to a relational database. It store data in tables, rows and columns. However in opposite to relational databases here each row can have its own format of the columns. Column databases can be seen as a two-dimensional key-value database. One of such database system is Apache Cassandra.
Warning: note that a “columnar database” and a “column database” are two different terms!
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