I am thinking about the best way to index my data. Is it a good idea to use the timestamp as my primary key? I am saving it anyway and I though about saving some columns. The timestamp should be an integer not a datetime column, because of performance. Moreover I don't want to be restricted on the amount of data in a short time (between two seconds). Therefore, I thought about an additionary AUTO_INCREMENT column. Now I have a unique key (timestamp and AI) and I can get the current inserted id easily by using the command "LAST_INSERT_ID". Is it possible to reset the AI counter every second / when there is a new timestamp? Or is it possible to detect if there is a dataset with the same timestamp and increase the AI value (I still want to be able to use LAST_INSERT_ID).
Please share some thoughts.
The timestamp should be an integer not a datetime column, because of performance.
I think you are of the belief that datetime
is stored as a string. It is stored as numbers quite efficiently and with a wider range andmore accuracy than an integer.
Using an integer may decrease performance because the database may not be able to correctly index it for use as a timestamp. It will complicate queries because you will not be able to use the full suite of date and time functions without first converting the integer to a datetime.
Use the appropriate date/time type, index it, and let the database optimize it.
Moreover I don't want to be restricted on the amount of data in a short time (between two seconds). Therefore, I thought about an [additional] AUTO_INCREEMENT column.
This would seem to defeat the point of "saving some columns". Now your primary key is two integers. Worse, it's a compound key which requires all references to store both values increasing storage requirements and complicating joins.
All the extra work necessary to determine the next primary key could be done in an insert trigger , but now you'd added complexity and extra work to every insert.
Is it a good idea to use the timestamp as my primary key?
A primary key should be A) unique and B) immutable. A timestamp is not unique, and you might need to change it.
Your primary key is unlikely to be a performance or storage bottleneck. Unless you have a good reason, stick with a simple, auto-incrementing big integer. A big integer because 2 billion is smaller than you think.
MySQL encapsulates this in serial
which is bigint unsigned not null auto_increment unique
.
TIMESTAMP
and DATETIME
are risky as a PRIMARY KEY
since the PK must be Unique.
Otherwise, it is fine to use them for the PK or an index. But here are some caveats:
=
first; put the datetime last.TIMESTAMP
and DATETIME
take 5 bytes (when not including microseconds); INT
is 4 bytes; BIGINT
is 8. country_code CHAR(2) CHARACTER SET ascii
is only 2 bytes -- better than 'normalizing' it and replacing it with a 4-byte cc_id INT
. You hinted at PRIMARY KEY(timestamp, ai)
:
INDEX(ai)
to keep AUTO_INCREMENT
happy.ai
, by itself.ai
big enough to last 'forever' before overflowing.
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