Question

How is a horizontal partitioning of a relation specified? How can a relation be put back together from a complete horizontal partitioning?

Short answer

A horizontal partitioning of a relation is specified by associating a boolean-condition with each set of tuples. To reconstruct a relation from horizontal partitions, SQL UNION operator can be utilized providing that each partition maintains the same structure.

Step-by-step solution

Understanding Horizontal Partitioning

Horizontal partitioning is a database design principle which deals with the division of a database into two or more tables. Each table then carries the same column structure but is responsible for maintaining and managing different subsets of the data. In other words, rows of a relation are distributed among different tables which are known as partitions.

Specifying Horizontal Partitioning

For specifying horizontal partitioning, a condition that estimates a true or false outcome for each tuple is associated with each partition. These conditions are specified by the designer based on applications needs and system performance. These could be based on range, value or a more complex condition. Let's say we have a relation R that has a partition condition P1, then the partition will include tuples such that each tuple T in R, if P1(T) = True then T is in that partition.

Reassembling from Horizontal Partitioning

A relation can be put back together from a complete horizontal partitioning using the SQL UNION operator. The UNION operator is used to combine the result-set of two or more SELECT statements (without returning any duplicate rows). Each partition is treated as a separate SELECT statement, and their result-sets are combined to form the original table. However, when using UNION, it is important to ensure that all SELECT statements have the same structure (same number of columns, same or compatible types, and in the same order).

Key concepts

Database Design

Database design is all about organizing data efficiently. Think of it as designing the layout of a house where each room has a specific purpose and function. In database design, each part of the database should serve a well-defined role.
Horizontal partitioning is a technique used in database design that divides a large database table into smaller, more manageable pieces called partitions. Each of these partitions has the same columns but contains different rows of data. This technique helps in making data retrieval faster because it narrows down the search to a specific subset of data rather than the entire dataset.
Good database design considers factors like the size of the data, the expected queries, and how often the data will be updated. When done right, it leads to more efficient applications and happier users because the system performs better under load.

SQL UNION Operator

The SQL UNION operator is a powerful tool in SQL used when you need to combine the results of multiple SELECT queries. It's like merging two pieces of a puzzle to see the whole picture.
When using the UNION operator, each SELECT statement within the UNION must have the same number of columns, and the corresponding columns must have similar data types. This ensures that the data can be combined seamlessly. The key feature of UNION is that it eliminates duplicate rows in the process, providing a clean and concise result.

• Use "UNION ALL" if you need duplicates.
• Great for reassembling partitions in horizontal partitioning.
• Helps manage large datasets by querying sections of data independently.

By understanding and applying the UNION operator, you can manage data more effectively in large systems.

Table Structure

The structure of a database table is like a blueprint. It defines how data is stored, what kind of data is stored, and how it relates to other data in the database.
In the context of horizontal partitioning, all tables that are part of a partition must have the same structure. Think of each partition as a slice of the original table, keeping the same column setup and data rules, but holding separate rows.

• Each table or partition has columns with defined data types.
• Indexes might be applied to make searches faster.
• Foreign keys can link tables together for complex queries.

When designing the table structure, you should plan for both current needs and future expansion. This ensures your database will stay effective as data grows.

Relation Reassembly

Relation reassembly refers to the process of combining data from partitions back into a single, cohesive dataset. It's like taking pieces of a pie and putting them back together to form a whole pie.
To achieve this, you use the SQL UNION operator which combines the results of each partition (viewed as separate tables) into a single output.

• All resulting sets of data must have the same column setup.
• Each partition's SELECT query should fetch the data in the same column order.
• Ensures no loss of data or structure upon reassembly.

Understanding relation reassembly is crucial when handling large datasets distributed across multiple partitions, ensuring that you can view and analyze data as if it were never partitioned.