Have you had experience using sequential table scans in a database?

A table scan is an operation where the database reads all the rows of a table sequentially without using indexes. This approach is typically used when:

• There is no suitable index for the query.
• The query returns a large portion of the table data.

In my experience working with Java and databases (such as PostgreSQL, MySQL), I have encountered situations where queries were slow due to sequential scans. To optimize, I used creating and tuning indexes, as well as rewriting queries to utilize indexes, which significantly improved performance.

Example: if you have a users table with a million records, and you run a query SELECT * FROM users WHERE age > 30, but there is no index on the age field, a full table scan will be performed, which is slow. Creating an index on age will allow the database to use the index and speed up the query.