What are horizontal and vertical partitions in database and what is the difference?

I read that

SELECT is a horizontal partition of the relation into two set of tuples.

and

PROJECT is a vertical partition of the relation into two relations.

However, I don't understand what that means. Can you explain it in layman's terms?

Solution 1:

Not a complete answer to the question but it answers what is asked in the question title. So the general meaning of horizontal and vertical database partitioning is:

Horizontal partitioning involves putting different rows into different tables. Perhaps customers with ZIP codes less than 50000 are stored in CustomersEast, while customers with ZIP codes greater than or equal to 50000 are stored in CustomersWest. The two partition tables are then CustomersEast and CustomersWest, while a view with a union might be created over both of them to provide a complete view of all customers.

Vertical partitioning involves creating tables with fewer columns and using additional tables to store the remaining columns. Normalization also involves this splitting of columns across tables, but vertical partitioning goes beyond that and partitions columns even when already normalized.

See more details here.

Solution 2:

A projection creates a subset of attributes in a relation hence a "vertical partition"

A selection creates a subset of the tuples in a relation hence a "horizontal partition"

Given a table (r) as

a : b : c : d : e
-----------------
1 : 2 : 3 : 4 : 5
1 : 2 : 3 : 4 : 5
2 : 2 : 3 : 4 : 5
2 : 2 : 3 : 4 : 5

An expression such as

PROJECT a, b (SELECT a=1 (r))

-- SELECT a, b FROM r WHERE a=1

Would "do"

a : b | c : d : e
-----------------
1 : 2 | 3 : 4 : 5
1 : 2 | 3 : 4 : 5
=================    <  -- horizontal partition (by SELECTION)
2 : 2 | 3 : 4 : 5
2 : 2 | 3 : 4 : 5

      ^  -- vertical partition (by PROJECTION)

Resulting in

a : b
------
1 : 2 
1 : 2