ClickHouse doesn't support, yet, DateTime with milliseconds.
I saw two possible suggestion regarding fields like: 2019-03-17T14:00:32.296Z
multiply by 100 an store it in UInt32/64. How do I use the multiply by 100 and store as UInt32?
to store milliseconds separately. Is there a way to remove milliseconds from 2019-03-17T14:00:32.296Z => 2019-03-17 14:00:32?
Thanks for your help!
Should use the datetime64 type - https://clickhouse.com/docs/en/sql-reference/data-types/datetime64/
In my mind, the main idea, why ClickHouse does not support milliseconds in DateTime is worse compression.
Long story short: use DateTime and precession by seconds. If you want to store milliseconds, you can go ahead with two ways:
Store milliseconds separately, so you will have a DateTime with your date, that you could use in all possible DateTime functions, as well as primary keys. And put milliseconds part in separate column with type UInt16. You have to prepare data separately before storing. Depends on what language do you use for preprocess data before storing, it could be different ways to do it. In golang it could be done:
time.Now().UnixNano() / 1e6 % 1e3
Another way, is to store whole as timestamp. This means you should convert your date to unix timestamp with milliseconds by your own and put it into ClickHouse as Uint64. It also depends on what do you use for preparing inserts. For golang it could like:
time.Now().UnixNano() / 1e6
Related
I have a field that contains time of order creation(order_time). Naturally, the best data type for that field is TIMESTAMP, but I want to create index and I'm not sure that TIMESTAMP index would be better than any numerical index. What's the best practice here?
I'm using oracle database
Always use the most appropriate data-type for the data:
If the data has date and time components and has a time-zone then use TIMESTAMP WITH TIME ZONE;
If the data has date and time components with fractional seconds and no time-zone then use TIMESTAMP;
If the data has date and time components with no fractional seconds and no time-zone then use DATE; and
If your data is an instant measured, for example, as the number of milliseconds (or seconds) since 1970-01-01 00:00:00 UTC and you almost entirely use it in its numeric form (i.e. you never, or very rarely, convert it to a human readable format such as YYYY-MM-DD HH:MI:SS.FF) then you may want to store it as a number. However, if you want to format it so it is readable or compare it to dates then you should prefer the TIMESTAMP (or DATE) data type.
Never use an inappropriate data-type for your column. The index performance between the different data-types should be mostly irrelevant and the overheads of converting from an inappropriate data-type to an appropriate one are likely to be a much more significant cost.
So, I am trying to build a query in RMAN Catalogue ( using RC_RMAN_BACKUP_JOB_DETAILS) to compare the most recent backup duration (TIME_TAKEN_DISPLAY) for each database (DB_NAME) with its historical average AVG backup duration (TIME_TAKEN_DISPLAY).
How do I convert TIME_TAKEN_DISPLAY(timestamp; HH:MM:SS), i.e. in VARCHAR2 Format to a minute format, i.e number only, so as to run the query against the entire RC_RMAN_BACKUP_JOB_DETAILS to compare AVG time taken in past with time takes for last backup for each DB.
One thing that may work is converting String(Time_taken_display)->To_TIME(Time_taken_display in Time format)->TO_NUM(Time_taken_display in minutes in number format), but this will be so highly inefficient.
The solution can be pretty simple and complex depending on the requirements:
One simple solution is:
select avg(substr(TIME_TAKEN_DISPLAY, 0,2)*60 + substr(TIME_TAKEN_DISPLAY, 4,2) + substr(TIME_TAKEN_DISPLAY, 7,2)/60) from RC_RMAN_BACKUP_JOB_DETAILS;
Using Type Casting Functions:
Cast TIME_TAKEN_DISPLAY into time format using TO_TIMESTAMP and then cast to TO_NUMBER, but I did not want to take this approach as I plan to run my scripts against all databases logged in the view, and multiple casting will leave the performance highly inefficient.
But as per #alex Poole comment, I will be using ENLAPSED_SECONDS field as it is readily available in seconds and number data type.
Suppose I need a field in tuple which should be date with time. Tarantool doesn't support date and time types out of the box.
I see two solutions:
Store date and time as string and parse it.
Store date and time in epoch seconds and convert it when needed.
What is the best solution to work with dates and times in Tarantool?
You should use UNIX time format (seconds since the beginning of the UNIX epoch) for two reasons:
- it's compact
- the desired ordering can be achieved with TREE index on 'unsigned' type.
If you deal with multiple time zones, it's best to convert to UNIX time before inserting into the database, and store the time zone in a separate field.
Support of datetime is an upcoming feature in Tarantool 2.10.0.
I have 2 timestamp columns stored in an HDFS that I can access through Impala, hive, etc...
The timestamps that I need to compare may look like this example:
2014-04-08 00:23:21.687000000
2014-04-08 00:23:21.620000000
With differences in the milliseconds, and need to build a new column that in this example should have a value of 0.067000
I've tried using impala's built in time functions but none of them seem to make the cut.
I've tried:
casting the string to a timestamp and then substracting the 2 values. This returns an error "AnalysisException: Arithmetic operation requires numeric operands"
using the unix_timestamp function. This truncates the values to an int that represent seconds, so subsecond values are lost.
While writting this question I found the answer :)
The way to do it was using a double cast.
Cast(cast(time_stamp) as timestamp) as double)
this makes the times_stamp into a number without truncating sub-second values.
Once there it becomes a trivial arithmetic operation.
How is Oracle date implemented? Is it stored as milliseconds or something like that?
An Oracle DATE stores the date and time to the second. An Oracle TIMESTAMP stores the date and time to up to 9 digits of subsecond precision, depending on the available hardware.
Both are implemented by storing the various components of the date and the time in a packed binary format. From the Oracle Concepts Guide section on dates
Oracle uses its own internal format to
store dates. Date data is stored in
fixed-length fields of seven bytes
each, corresponding to century, year,
month, day, hour, minute, and second.
You can use the DUMP() function to see the internal representation of any particular date (or any other value for that matter), but that's probably more than you need (or want) to know.
Apparently, not in form of millisecs.
Which actually makes sense, since they do not have any running operations on current date/time:
http://www.ixora.com.au/notes/date_representation.htm
http://infolab.stanford.edu/~ullman/fcdb/oracle/or-time.html
http://www.akadia.com/services/ora_date_time.html
No. DATE is a timestamp value with seconds precision. You need TIMESTAMP(3) to store milliseconds.