Delimited Lists vs. Normalized Tables in SQL: Which Approach Offers Better Query Efficiency?

Efficiency Comparison: Delimited List vs Normalized Tables

In SQL databases, representing lists can be achieved using two different approaches: storing them as a comma-separated string in a single column or creating a separate row for each list item. This article delves into the efficiency trade-offs of these methods.

Delimited List Approach

In this approach, a list is represented as a single entry in a column using a delimiter (e.g., comma). This format is exemplified by the following table:

Value

List

Value3

Value4

Value	List	Value3	Value4
value	a,b,c,d,e,f,g,h,i,j	value3	value4

value

a,b,c,d,e,f,g,h,i,j

value3

value4

Normalized Approach

Value	Item	Value3	Value4
value	a	value3	value4
value	b	value3	value4
value	c	value3	value4
...	...	...	...
value	j	value3	value4

In contrast, the normalized approach creates a separate row for each list item, resulting in a table with a different structure:

Query Efficiency

The choice between these approaches should consider query efficiency. Using the LIKE operator to search for a specific item in the delimited list approach is often inefficient because it cannot leverage indexes. This can lead to slow performance, especially for large tables.

Normalized Table Advantage

The normalized approach, however, enables efficient queries using the equals (=) operator. By creating separate rows for each list item, the database can use indexes to speed up searches. In the example provided, where the table has approximately 10,000 rows with an average of 8 list items each, the normalized approach would result in a significant performance improvement.

Conclusion

When deciding between a delimited list and a normalized table for representing lists in SQL databases, the normalized table approach is generally preferred for better query efficiency. It allows for faster searches and is considered a more efficient and flexible design pattern for RDBMS applications.

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