What are SQL Indexes and how to create one? (For Beginners)

Indexes are lookup tables that when used speed up data retrival within a voluminous table.

I'll appreciate your feedback so I can improve on the sketches.

Comments

[giuliovn]

What happens if there is more than one result?

[alokz diptim!]

Good question Giuliovn.

Once a table is indexed based on a column field, a lookup table would be created that references the normal SQL table through the row address column.

So, for example if there are multiple instances of transaction amount, the row address in the lookup table would be pointing to the exact multiple row instance in the transaction table.

Therefore,

Select * from transaction where transactionAmount = 5000

For a multiple resultset won't be a table scan.

[Katie Nelson]

Your sketches are awesome and very clear.

[alokz diptim!]

Thanks Katie for the feedback:)