Greetings,
I am trying to get a feel of how MySQL would handle certain types of
situation, mainly concerning the usage of indices.
Say I have two exactly identical table structures namely table A & B.
For table A, I just have one composite primary key on (Code, Date1 &
Date2).
For table B, I just have composite primary key on (Code, Date1 & Date2)
and two non-unique keys on Date1 & Date2.
Question is, Will I find any performance improvement with table B, If
all my queries start with Code field ?
In other words : Will there be any noticiable difference in speed for
query "Select * from tableB where code = cd and dt1 > $one_year_ago" over
the same query on tableA ?
Kindly note that we might have 1000 or more records for each code. When
I tried to do an explain, it suggested in both the cases (on tableA & on
tableB) that It will use composite primary key (mainly because left most
field in the primary index is avaliable)....suggesting that the non-unique
indices are pretty much a waste of space...Is that really the case? Woudln't
it be "optimal" to use primary key + non-unique key combination to narrow
down the search?
I would greatly appreciate your insight in this issue.
TIA
Manoj
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