What is the algorithm for query search in the database?

Question

Good day everyone, I\'m currently doing research on search algorithm optimization.

As of now, I\'m researching on the Database.

In a database w/ SQL Support.

Answer 1

If there's no indexes, then yes, a linear search is performed.

But, databases typically use a B Tree index when you specify a column(s) as a key. These are special data structure formats that are specifically tuned(high B Tree branching factors) to perform well on magnetic disk hardware, where the most significant time consuming factor is the seek operation(the magnetic head has to move to a diff part of the file).

You can think of the index as a sorted/structured copy of the values in a column. It can be determined quickly if the value being searched for is in the index. If it finds it, then it will also find a pointer that points back to the correct location of the corresponding row in the main data file(so it can go and read the other columns in the row). Sometimes a multi-column index contains all the data requested by the query, and then it doesn't need to skip back to the main file, it can just read what it found and then its done.

There's other types of indexes, but I think you get the idea - duplicate data and arrange it in a way that's fast to search.

On a large database, indexes make the difference between waiting a fraction of a second, vs possibly days for a complex query to complete.

btw- B tree's aren't a simple and easy to understand data structure, and the traversal algorithm is also complex. In addition, the traversal is even uglier than most of the code you will find, because in a database they are constantly loading/unloading chunks of data from disk and managing it in memory, and this significantly uglifies the code. But, if you're familiar with binary search trees, then I think you understand the concept well enough.