This question suddenly popped into my head… I have a table that ties two other tables together based on their ID. The CREATE TABLE
looks like this:
CREATE TABLE `ticket_contact` (
`ticket_id` INT NOT NULL,
`entity_id` INT NOT NULL,
`notify` INT NOT NULL DEFAULT 0,
PRIMARY KEY (`ticket_id`, `entity_id`),
KEY `ticket_id` (`ticket_id`),
KEY `entity_id` (`entity_id`)
)
I'm wondering if there is any need to include those last two KEY
lines. Will it give me improved speed with the following queries, or will individual columns within a PRIMARY KEY
automatically be indexed?
SELECT * FROM ticket_contact WHERE ticket_id=1;
SELECT * FROM ticket_contact WHERE entity_id=1;
Best Answer
An index created by
PRIMARY KEY
is the same as any other (potentially composite)UNIQUE
index. So you needn't create a separate index forticket_id
as it is included as the major column in the(ticket_id, entity_id)
index.You would want to create a separate index over
entity_id
if you were commonly doing queries using that column independently of theticket_id
.