Question

Do splitting fields into multiple tables ever yield faster queries? Consider the following two scenarios:

Table1
-----------
int PersonID
text Value1
float Value2

or

Table1
-----------
int PersonID
text Value1

Table2
-----------
int PersonID
float Value2

If Value1 and Value2 are always being displayed together, I imagine the first scenario is always faster because the second schema would require two SELECT statements.

But are there any situations where you would choose the second? If the number of records were expected to be really large?

Answer 1

This is called Vertical partitioning, and in some specific situations, may yield better performance.

From Wikipedia:

Vertical partitioning goes beyond normalization and partitions columns even when already normalized. Different physical storage might be used to realize vertical partitioning as well; storing infrequently used or very wide columns on a different device, for example, is a method of vertical partitioning.

A common form of vertical partitioning is to split (slow to find) dynamic data from (fast to find) static data in a table where the dynamic data is not used as often as the static.

Creating a view across the two newly created tables restores the original table with a performance penalty, however performance will increase when accessing the static data e.g. for statistical analysis.

You may be interested in checking out the following article, on how, when, and for how long MySpace used vertical partitioning to tackle its scalibiliy issues:

• High Scalability: MySpace Architecture