Index question: Select * with WHERE clause. Where and how to create index
- by Mestika
Hi,
I’m working on optimizing some of my queries and I have a query that states:
select * from SC where c_id ="+c_id”
The schema of ** SC** looks like this:
SC ( c_id int not null, date_start date not null, date_stop date not null, r_t_id int not null, nt int, t_p decimal, PRIMARY KEY (c_id, r_t_id, date_start, date_stop));
My immediate bid on how the index should be created is a covering index in this order:
INDEX(c_id, date_start, date_stop, nt, r_t_id, t_p)
The reason for this order I base on:
The WHERE clause selects from c_id thus making it the first sorting order.
Next, the date_start and date_stop to specify a sort of “range” to be defined in these parameters
Next, nt because it will select the nt
Next the r_t_id because it is a ID for a specific type of my r_t table
And last the t_p because it is just a information.
I don’t know if it is at all necessary to order it in a specific way when it is a SELECT ALL statement.
I should say, that the SC is not the biggest table. I can say how many rows it contains but a estimate could be between <10 and 1000.
The next thing to add is, that the SC, in different queries, inserts the data into the SC, and I know that indexes on tables which have insertions can be cost ineffective, but can I somehow create a golden middle way to effective this performance.
Don't know if it makes a different but I'm using IBM DB2 version 9.7 database
Sincerely
Mestika
