Indexes are utilized to find rows with specific column values rapidly. With no index, MySQL must start with the very first row after which read car table to obtain the relevant rows.
States our beloved MySQL manual.
For the reason that situation, how about we just index every column?
And also, since I've these feelings that it might be a larger hit to performance, when must we use indexes/guidelines for indexes?
Thanks ahead of time!
Creating a catalog always comes at a price: The greater indices you've on the table, the greater costly it's to modify that table (i.e. card inserts, updates and removes take more time).
Consequently, queries that may use the indices is going to be faster. It is a classical tradeoff. Of all tables a small amount of generally used indices may be worth the price, because queries happen frequently enough (or their performance is a lot more important compared to modification performance).
However, for those who have some type of log table that's up-to-date very frequently, but queried only hardly ever (for instance just in case of the catastrophic failure), then adding a catalog would give a large cost and supply hardly any advantage.
Also: whether a catalog is helpful is dependent a great deal around the exact query to become performed. It is possible you have indices spanning each column, however the query can't utilize it since the indices have been in the incorrect order, possess the wrong information or even the wrong format. So not every indices help all queries.
Because of your logic, you would not index just every column, but every permutation of each and every column. The overhead involved with storing these details, maintaining true it current, could be absolutely huge.
Generally index is useful if it features a good selectivity, i.e. once the query chooses just a little part of data in line with the value (or range) of indexed attribute.
Also indice are great for merge joins, when sorting rows with a joining attribute both in became a member of tables enables to complement rows and retrieve data in a single pass.
Because it had been pointed out, indexes decelerate updates and occupy some memory (which, alone, slows lower performance too)