It refers to the division of a relation into subsets (fragments) of tuples (rows). Each fragment is stored at a different node, and each fragment has unique rows. However, the unique rows all have the same attributes (columns). In short, each fragment represents the equivalent of a SELECT statement, with the WHERE clause on a single attribute.
It refers to the division of a relation into attribute (column) subsets. Each subset (fragment) is stored at a different node, and each fragment has unique columns—with the exception of the key column, which is common to all fragments.
Types of horizontal fragmentation
i. Primary Horizontal Fragmentation
It is the fragmentation of primary relation
e.g. Employee table is fragmented for Department No.
ii. Derived Horizontal Fragmentation
Fragmentation of the secondary relations that are dependent on the primary relation; related with foreign keys.