impala/docs/topics/impala_timestamp.xml

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<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="timestamp">

  <title>TIMESTAMP Data Type</title>
  <titlealts audience="PDF"><navtitle>TIMESTAMP</navtitle></titlealts>
  <prolog>
    <metadata>
      <data name="Category" value="Impala"/>
      <data name="Category" value="Impala Data Types"/>
      <data name="Category" value="SQL"/>
      <data name="Category" value="Data Analysts"/>
      <data name="Category" value="Developers"/>
      <data name="Category" value="Dates and Times"/>
    </metadata>
  </prolog>

  <conbody>

    <p>
      A data type used in <codeph>CREATE TABLE</codeph> and <codeph>ALTER TABLE</codeph> statements, representing a
      point in time.
    </p>

    <p conref="../shared/impala_common.xml#common/syntax_blurb"/>

    <p>
      In the column definition of a <codeph>CREATE TABLE</codeph> statement:
    </p>

<codeblock><varname>column_name</varname> TIMESTAMP</codeblock>

    <p>
      <b>Range:</b> Allowed date values range from 1400-01-01 to 9999-12-31; this range is different from the Hive
      <codeph>TIMESTAMP</codeph> type. Internally, the resolution of the time portion of a
      <codeph>TIMESTAMP</codeph> value is in nanoseconds.
    </p>

    <p>
      <b>INTERVAL expressions:</b>
    </p>

    <p>
      You can perform date arithmetic by adding or subtracting a specified number of time units, using the
      <codeph>INTERVAL</codeph> keyword and the <codeph>+</codeph> and <codeph>-</codeph> operators or
      <codeph>date_add()</codeph> and <codeph>date_sub()</codeph> functions. You can specify units as
      <codeph>YEAR[S]</codeph>, <codeph>MONTH[S]</codeph>, <codeph>WEEK[S]</codeph>, <codeph>DAY[S]</codeph>,
      <codeph>HOUR[S]</codeph>, <codeph>MINUTE[S]</codeph>, <codeph>SECOND[S]</codeph>,
      <codeph>MILLISECOND[S]</codeph>, <codeph>MICROSECOND[S]</codeph>, and <codeph>NANOSECOND[S]</codeph>. You can
      only specify one time unit in each interval expression, for example <codeph>INTERVAL 3 DAYS</codeph> or
      <codeph>INTERVAL 25 HOURS</codeph>, but you can produce any granularity by adding together successive
      <codeph>INTERVAL</codeph> values, such as <codeph><varname>timestamp_value</varname> + INTERVAL 3 WEEKS -
      INTERVAL 1 DAY + INTERVAL 10 MICROSECONDS</codeph>.
    </p>

    <p>
      For example:
    </p>

<codeblock>select now() + interval 1 day;
select date_sub(now(), interval 5 minutes);
insert into auction_details
  select auction_id, auction_start_time, auction_start_time + interval 2 days + interval 12 hours
  from new_auctions;</codeblock>

    <p>
      <b>Time zones:</b>
    </p>

    <p>
      By default, Impala does not store timestamps using the local timezone, to avoid undesired results from
      unexpected time zone issues. Timestamps are stored and interpreted relative to UTC, both when written to or
      read from data files, or when converted to or from Unix time values through functions such as
      <codeph>from_unixtime()</codeph> or <codeph>unix_timestamp()</codeph>. To convert such a
      <codeph>TIMESTAMP</codeph> value to one that represents the date and time in a specific time zone, convert
      the original value with the <codeph>from_utc_timestamp()</codeph> function.
    </p>

    <p>
      Because Impala does not assume that <codeph>TIMESTAMP</codeph> values are in any particular time zone, you
      must be conscious of the time zone aspects of data that you query, insert, or convert.
    </p>

    <p>
      For consistency with Unix system calls, the <codeph>TIMESTAMP</codeph> returned by the <codeph>now()</codeph>
      function represents the local time in the system time zone, rather than in UTC. To store values relative to
      the current time in a portable way, convert any <codeph>now()</codeph> return values using the
      <codeph>to_utc_timestamp()</codeph> function first. For example, the following example shows that the current
      time in California (where this Impala cluster is located) is shortly after 2 PM. If that value was written to a data
      file, and shipped off to a distant server to be analyzed alongside other data from far-flung locations, the
      dates and times would not match up precisely because of time zone differences. Therefore, the
      <codeph>to_utc_timestamp()</codeph> function converts it using a common reference point, the UTC time zone
      (descended from the old Greenwich Mean Time standard). The <codeph>'PDT'</codeph> argument indicates that the
      original value is from the Pacific time zone with Daylight Saving Time in effect. When servers in all
      geographic locations run the same transformation on any local date and time values (with the appropriate time
      zone argument), the stored data uses a consistent representation. Impala queries can use functions such as
      <codeph>EXTRACT()</codeph>, <codeph>MIN()</codeph>, <codeph>AVG()</codeph>, and so on to do time-series
      analysis on those timestamps.
    </p>

<codeblock>[localhost:21000] > select now();
+-------------------------------+
| now()                         |
+-------------------------------+
| 2015-04-09 14:07:46.580465000 |
+-------------------------------+
[localhost:21000] > select to_utc_timestamp(now(), 'PDT');
+--------------------------------+
| to_utc_timestamp(now(), 'pdt') |
+--------------------------------+
| 2015-04-09 21:08:07.664547000  |
+--------------------------------+
</codeblock>

    <p>
      The converse function, <codeph>from_utc_timestamp()</codeph>, lets you take stored <codeph>TIMESTAMP</codeph>
      data or calculated results and convert back to local date and time for processing on the application side.
      The following example shows how you might represent some future date (such as the ending date and time of an
      auction) in UTC, and then convert back to local time when convenient for reporting or other processing. The
      final query in the example tests whether this arbitrary UTC date and time has passed yet, by converting it
      back to the local time zone and comparing it against the current date and time.
    </p>

<codeblock>[localhost:21000] > select to_utc_timestamp(now() + interval 2 weeks, 'PDT');
+---------------------------------------------------+
| to_utc_timestamp(now() + interval 2 weeks, 'pdt') |
+---------------------------------------------------+
| 2015-04-23 21:08:34.152923000                     |
+---------------------------------------------------+
[localhost:21000] > select from_utc_timestamp('2015-04-23 21:08:34.152923000','PDT');
+------------------------------------------------------------+
| from_utc_timestamp('2015-04-23 21:08:34.152923000', 'pdt') |
+------------------------------------------------------------+
| 2015-04-23 14:08:34.152923000                              |
+------------------------------------------------------------+
[localhost:21000] > select from_utc_timestamp('2015-04-23 21:08:34.152923000','PDT') &lt; now();
+--------------------------------------------------------------------+
| from_utc_timestamp('2015-04-23 21:08:34.152923000', 'pdt') &lt; now() |
+--------------------------------------------------------------------+
| false                                                              |
+--------------------------------------------------------------------+
</codeblock>

    <p rev="2.2.0">
      If you have data files written by Hive, those <codeph>TIMESTAMP</codeph> values represent the local timezone
      of the host where the data was written, potentially leading to inconsistent results when processed by Impala.
      To avoid compatibility problems or having to code workarounds, you can specify one or both of these
      <cmdname>impalad</cmdname> startup flags: <codeph>-use_local_tz_for_unix_timestamp_conversions=true</codeph>
      <codeph>-convert_legacy_hive_parquet_utc_timestamps=true</codeph>. Although
      <codeph>-convert_legacy_hive_parquet_utc_timestamps</codeph> is turned off by default to avoid performance overhead, <ph rev="upstream">Cloudera</ph> recommends
      turning it on when processing <codeph>TIMESTAMP</codeph> columns in Parquet files written by Hive, to avoid unexpected behavior.
    </p>

    <p rev="2.2.0">
      The <codeph>-use_local_tz_for_unix_timestamp_conversions</codeph> setting affects conversions from
      <codeph>TIMESTAMP</codeph> to <codeph>BIGINT</codeph>, or from <codeph>BIGINT</codeph>
      to <codeph>TIMESTAMP</codeph>. By default, Impala treats all <codeph>TIMESTAMP</codeph> values as UTC,
      to simplify analysis of time-series data from different geographic regions. When you enable the
      <codeph>-use_local_tz_for_unix_timestamp_conversions</codeph> setting, these operations
      treat the input values as if they are in the local tie zone of the host doing the processing.
      See <xref href="impala_datetime_functions.xml#datetime_functions"/> for the list of functions
      affected by the <codeph>-use_local_tz_for_unix_timestamp_conversions</codeph> setting.
    </p>

    <p>
      The following sequence of examples shows how the interpretation of <codeph>TIMESTAMP</codeph> values in
      Parquet tables is affected by the setting of the <codeph>-convert_legacy_hive_parquet_utc_timestamps</codeph>
      setting.
    </p>

    <p>
      Regardless of the <codeph>-convert_legacy_hive_parquet_utc_timestamps</codeph> setting,
      <codeph>TIMESTAMP</codeph> columns in text tables can be written and read interchangeably by Impala and Hive:
    </p>

<codeblock>Impala DDL and queries for text table:

[localhost:21000] > create table t1 (x timestamp);
[localhost:21000] > insert into t1 values (now()), (now() + interval 1 day);
[localhost:21000] > select x from t1;
+-------------------------------+
| x                             |
+-------------------------------+
| 2015-04-07 15:43:02.892403000 |
| 2015-04-08 15:43:02.892403000 |
+-------------------------------+
[localhost:21000] > select to_utc_timestamp(x, 'PDT') from t1;
+-------------------------------+
| to_utc_timestamp(x, 'pdt')    |
+-------------------------------+
| 2015-04-07 22:43:02.892403000 |
| 2015-04-08 22:43:02.892403000 |
+-------------------------------+

Hive query for text table:

hive> select * from t1;
OK
2015-04-07 15:43:02.892403
2015-04-08 15:43:02.892403
Time taken: 1.245 seconds, Fetched: 2 row(s)
</codeblock>

    <p>
      When the table uses Parquet format, Impala expects any time zone adjustment to be applied prior to writing,
      while <codeph>TIMESTAMP</codeph> values written by Hive are adjusted to be in the UTC time zone. When Hive
      queries Parquet data files that it wrote, it adjusts the <codeph>TIMESTAMP</codeph> values back to the local
      time zone, while Impala does no conversion. Hive does no time zone conversion when it queries Impala-written
      Parquet files.
    </p>

<codeblock>Impala DDL and queries for Parquet table:

[localhost:21000] > create table p1 stored as parquet as select x from t1;
+-------------------+
| summary           |
+-------------------+
| Inserted 2 row(s) |
+-------------------+
[localhost:21000] > select x from p1;
+-------------------------------+
| x                             |
+-------------------------------+
| 2015-04-07 15:43:02.892403000 |
| 2015-04-08 15:43:02.892403000 |
+-------------------------------+

Hive DDL and queries for Parquet table:

hive> create table h1 (x timestamp) stored as parquet;
OK
hive> insert into h1 select * from p1;
...
OK
Time taken: 35.573 seconds
hive> select x from p1;
OK
2015-04-07 15:43:02.892403
2015-04-08 15:43:02.892403
Time taken: 0.324 seconds, Fetched: 2 row(s)
hive> select x from h1;
OK
2015-04-07 15:43:02.892403
2015-04-08 15:43:02.892403
Time taken: 0.197 seconds, Fetched: 2 row(s)
</codeblock>

    <p>
      The discrepancy arises when Impala queries the Hive-created Parquet table. The underlying values in the
      <codeph>TIMESTAMP</codeph> column are different from the ones written by Impala, even though they were copied
      from one table to another by an <codeph>INSERT ... SELECT</codeph> statement in Hive. Hive did an implicit
      conversion from the local time zone to UTC as it wrote the values to Parquet.
    </p>

<codeblock>Impala query for TIMESTAMP values from Impala-written and Hive-written data:

[localhost:21000] > select * from p1;
+-------------------------------+
| x                             |
+-------------------------------+
| 2015-04-07 15:43:02.892403000 |
| 2015-04-08 15:43:02.892403000 |
+-------------------------------+
Fetched 2 row(s) in 0.29s
[localhost:21000] > select * from h1;
+-------------------------------+
| x                             |
+-------------------------------+
| 2015-04-07 22:43:02.892403000 |
| 2015-04-08 22:43:02.892403000 |
+-------------------------------+
Fetched 2 row(s) in 0.41s

Underlying integer values for Impala-written and Hive-written data:

[localhost:21000] > select cast(x as bigint) from p1;
+-------------------+
| cast(x as bigint) |
+-------------------+
| 1428421382        |
| 1428507782        |
+-------------------+
Fetched 2 row(s) in 0.38s
[localhost:21000] > select cast(x as bigint) from h1;
+-------------------+
| cast(x as bigint) |
+-------------------+
| 1428446582        |
| 1428532982        |
+-------------------+
Fetched 2 row(s) in 0.20s
</codeblock>

    <p>
      When the <codeph>-convert_legacy_hive_parquet_utc_timestamps</codeph> setting is enabled, Impala recognizes
      the Parquet data files written by Hive, and applies the same UTC-to-local-timezone conversion logic during
      the query as Hive uses, making the contents of the Impala-written <codeph>P1</codeph> table and the
      Hive-written <codeph>H1</codeph> table appear identical, whether represented as <codeph>TIMESTAMP</codeph>
      values or the underlying <codeph>BIGINT</codeph> integers:
    </p>

<codeblock>[localhost:21000] > select x from p1;
+-------------------------------+
| x                             |
+-------------------------------+
| 2015-04-07 15:43:02.892403000 |
| 2015-04-08 15:43:02.892403000 |
+-------------------------------+
Fetched 2 row(s) in 0.37s
[localhost:21000] > select x from h1;
+-------------------------------+
| x                             |
+-------------------------------+
| 2015-04-07 15:43:02.892403000 |
| 2015-04-08 15:43:02.892403000 |
+-------------------------------+
Fetched 2 row(s) in 0.19s
[localhost:21000] > select cast(x as bigint) from p1;
+-------------------+
| cast(x as bigint) |
+-------------------+
| 1428446582        |
| 1428532982        |
+-------------------+
Fetched 2 row(s) in 0.29s
[localhost:21000] > select cast(x as bigint) from h1;
+-------------------+
| cast(x as bigint) |
+-------------------+
| 1428446582        |
| 1428532982        |
+-------------------+
Fetched 2 row(s) in 0.22s
</codeblock>

    <p>
      <b>Conversions:</b>
    </p>

    <p conref="../shared/impala_common.xml#common/timestamp_conversions"/>

    <p>
      In Impala 1.3 and higher, the <codeph>FROM_UNIXTIME()</codeph> and <codeph>UNIX_TIMESTAMP()</codeph>
      functions allow a wider range of format strings, with more flexibility in element order, repetition of letter
      placeholders, and separator characters. In <keyword keyref="impala23_full"/> and higher, the <codeph>UNIX_TIMESTAMP()</codeph>
      function also allows a numeric timezone offset to be specified as part of the input string.
      See <xref href="impala_datetime_functions.xml#datetime_functions"/> for details.
    </p>

    <p conref="../shared/impala_common.xml#common/y2k38"/>

    <p>
      <b>Partitioning:</b>
    </p>

    <p>
      Although you cannot use a <codeph>TIMESTAMP</codeph> column as a partition key, you can extract the
      individual years, months, days, hours, and so on and partition based on those columns. Because the partition
      key column values are represented in HDFS directory names, rather than as fields in the data files
      themselves, you can also keep the original <codeph>TIMESTAMP</codeph> values if desired, without duplicating
      data or wasting storage space. See <xref href="impala_partitioning.xml#partition_key_columns"/> for more
      details on partitioning with date and time values.
    </p>

<codeblock>[localhost:21000] &gt; create table timeline (event string) partitioned by (happened timestamp);
ERROR: AnalysisException: Type 'TIMESTAMP' is not supported as partition-column type in column: happened
</codeblock>

    <p conref="../shared/impala_common.xml#common/example_blurb"/>

<codeblock>select cast('1966-07-30' as timestamp);
select cast('1985-09-25 17:45:30.005' as timestamp);
select cast('08:30:00' as timestamp);
select hour('1970-01-01 15:30:00');         -- Succeeds, returns 15.
select hour('1970-01-01 15:30');            -- Returns NULL because seconds field required.
select hour('1970-01-01 27:30:00');         -- Returns NULL because hour value out of range.
select dayofweek('2004-06-13');             -- Returns 1, representing Sunday.
select dayname('2004-06-13');               -- Returns 'Sunday'.
select date_add('2004-06-13', 365);         -- Returns 2005-06-13 with zeros for hh:mm:ss fields.
select day('2004-06-13');                   -- Returns 13.
select datediff('1989-12-31','1984-09-01'); -- How many days between these 2 dates?
select now();                               -- Returns current date and time in local timezone.

create table dates_and_times (t timestamp);
insert into dates_and_times values
  ('1966-07-30'), ('1985-09-25 17:45:30.005'), ('08:30:00'), (now());
</codeblock>

    <p conref="../shared/impala_common.xml#common/null_bad_timestamp_cast"/>

    <p conref="../shared/impala_common.xml#common/partitioning_worrisome"/>

    <p conref="../shared/impala_common.xml#common/hbase_ok"/>

    <p conref="../shared/impala_common.xml#common/parquet_ok"/>

    <p conref="../shared/impala_common.xml#common/text_bulky"/>

<!--    <p conref="../shared/impala_common.xml#common/compatibility_blurb"/> -->

    <p conref="../shared/impala_common.xml#common/internals_16_bytes"/>

    <p conref="../shared/impala_common.xml#common/added_forever"/>

    <p conref="../shared/impala_common.xml#common/column_stats_constant"/>

    <p conref="../shared/impala_common.xml#common/sqoop_blurb"/>

    <p conref="../shared/impala_common.xml#common/sqoop_timestamp_caveat"/>

    <p conref="../shared/impala_common.xml#common/restrictions_blurb"/>

    <p>
      If you cast a <codeph>STRING</codeph> with an unrecognized format to a <codeph>TIMESTAMP</codeph>, the result
      is <codeph>NULL</codeph> rather than an error. Make sure to test your data pipeline to be sure any textual
      date and time values are in a format that Impala <codeph>TIMESTAMP</codeph> can recognize.
    </p>

    <p conref="../shared/impala_common.xml#common/avro_no_timestamp"/>

    <p conref="../shared/impala_common.xml#common/related_info"/>

    <ul>
      <li>
<!-- The Timestamp Literals topic is pretty brief. Consider adding more examples there. -->
        <xref href="impala_literals.xml#timestamp_literals"/>.
      </li>

      <li>
        To convert to or from different date formats, or perform date arithmetic, use the date and time functions
        described in <xref href="impala_datetime_functions.xml#datetime_functions"/>. In particular, the
        <codeph>from_unixtime()</codeph> function requires a case-sensitive format string such as
        <codeph>"yyyy-MM-dd HH:mm:ss.SSSS"</codeph>, matching one of the allowed variations of a
        <codeph>TIMESTAMP</codeph> value (date plus time, only date, only time, optional fractional seconds).
      </li>

      <li>
        See <xref href="impala_langref_unsupported.xml#langref_hiveql_delta"/> for details about differences in
        <codeph>TIMESTAMP</codeph> handling between Impala and Hive.
      </li>
    </ul>

  </conbody>

</concept>