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.. index:: Reference; SQL
SQL Reference
=============
The query language supported by **odc** is a small subset of `SQL (Structured Query Language)`_ with a few domain-specific extensions, most notably `bitfields`_ allow for naming and accessing sequences of bits in a column.
.. note::
All example commands on this page can be run against the following file:
* :download:`example.odb </_static/example.odb>`
The examples assume the **odc** binary is in your ``$PATH``.
Built-in Functions
------------------
Scalar Functions
~~~~~~~~~~~~~~~~
Scalar functions return a single value, based on one or more input values.
+------------------------------------------------+-------+-------------------------------------------------------------+
| Function | Arity | Description |
+================================================+=======+=============================================================+
| ``year(date)`` | ``1`` | Returns the year part of ``date`` |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``month(date)`` | ``1`` | Returns the month part of ``date`` |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``day(date)`` | ``1`` | Returns the day part of ``date`` |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``hour(time)`` | ``1`` | Returns the hour part of ``time`` |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``minute(time)`` | ``1`` | Returns the minute part of ``time`` |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``second(time)`` | ``1`` | Returns the second part of ``time`` |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``timestamp(date, time)`` | ``2`` | Returns the timestamp of ``date`` and ``time`` values |
| | | (format: ``YYYYMMDDHHMMSS``) |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``julian_seconds(date, time)`` | ``2`` | Returns the number of Julian seconds of ``date`` and |
| | | ``time`` values |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``julian(date, time)`` or ``jd(date, time)`` | ``2`` | Returns the Julian date of ``date`` and ``time`` values |
| or ``julian_date(date, time)`` | | |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``tdiff(tgdate, tgtime, andate, antime)`` | ``4`` | Time difference in seconds (``tgdate``, ``tgtime``) are |
| | | target times from which the nominal analysis timestamp |
| | | (``andate``, ``antime``) is getting subtracted from |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``cos(x)`` | ``1`` | Cosine (where ``x`` is in degrees) |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``sin(x)`` | ``1`` | Sine (where ``x`` is in degrees) |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``tan(x)`` | ``1`` | Tangent (where ``x`` is in degrees) |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``acos(x)`` | ``1`` | Arc cosine (the result is in degrees) |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``asin(x)`` | ``1`` | Arc sine (the result is in degrees) |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``atan(x)`` | ``1`` | Arc tangent (the result is in degrees) |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``atan2(x, y)`` | ``2`` | Arc tangent of two variables (the result in degrees) |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``exp(x)`` | ``1`` | Exponent |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``ldexp_double(x,n)`` | ``2`` | Returns multiplied floating point value ``x`` by the number |
| | | 2 raised to ``n`` power (:math:`x*2^n`) |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``cosh(x)`` | ``1`` | Hyperbolic cosine |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``sinh(x)`` | ``1`` | Hyperbolic sine |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``tanh(x)`` | ``1`` | Hyperbolic tangent |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``int(x)`` or ``trunc(x)`` | ``1`` | Truncate to integer |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``nint(x)`` | ``1`` | Round-up to integer |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``floor(x)`` | ``1`` | Calculate floor value |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``ceil(x)`` | ``1`` | Calculate ceiling value |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``abs(x)`` or ``fabs(x)`` | ``1`` | Absolute value |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``ibits(x, pos, len)`` | ``3`` | Extract ``len`` bits from ``x`` offset ``pos`` |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``mod(x, y)`` | ``2`` | ``x`` modulo ``y`` with floating point numbers accepted |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``pow(x, y)`` | ``2`` | ``x`` power of ``y`` (:math:`x^y`) |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``sqrt(x)`` | ``1`` | Square root (:math:`\sqrt{x}`) |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``log(x)`` or ``ln(x)`` | ``1`` | Natural logarithm |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``log10(x)`` or ``lg(x)`` | ``1`` | Base-10 logarithm |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``deg2rad(x)`` or ``radians(x)`` | ``1`` | Convert degrees to radians |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``rad2deg(x)`` or ``degrees(x)`` | ``1`` | Convert radians to degrees |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``celsius(x)`` or ``k2c(x)`` | ``1`` | Convert Kelvin to Celsius |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``c2k(x)`` | ``1`` | Convert Celsius to Kelvin |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``fahrenheit(x)`` or ``k2f(x)`` | ``1`` | Convert Kelvin to Fahrenheit |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``f2k(x)`` | ``1`` | Convert Fahrenheit to Kelvin |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``c2f(x)`` | ``1`` | Convert Celsius to Fahrenheit |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``f2c(x)`` | ``1`` | Convert Fahrenheit to Celsius |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``circle(x, x0, y, y0, r)`` | ``4`` | Returns ``1``, if the point (``x``, ``y``) is inside (or |
| | | on) the (planar) circle with origin at (``x0``, ``y0``) |
| | | and radius ``r`` |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``rad(lat0, lon0, angle, lat, lon)`` | ``4`` | Returns ``1``, if the (``lat``, ``lon``) is inside the |
| | | great-circle (of any radius) with origin (``lat0``, |
| | | ``lon0``) and view ``angle`` (in degrees) |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``distance(lat1, lon1, lat2, lon2)`` | ``4`` | Distance (expressed in metres) between two positions |
| | | (``lat1``, ``lon1``) and (``lat2``, ``lon2``) along a |
| | | great-circle of the Earth (``R=6371km``) |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``km(lat1, lon1, lat2, lon2)`` | ``4`` | Synonym of ``distance`` function, but expressed in |
| | | kilometres |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``dist(reflat, reflon, refdist_km, lat, lon)`` | ``5`` | Returns 1, if (``lat``, ``lon``) is inside the great-circle |
| | | of radius ``refdist_km`` (in kilometres) with origin |
| | | (``reflat``, ``reflon``) |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``rownumber()`` | ``0`` | Returns the current row number, indexed at 1 |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``nvl(expression, alt_value)`` | ``2`` | Returns an ``alt_value`` when ``expression`` is null |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``speed(u, v)`` or ``ff(u, v)`` | ``2`` | Returns wind speed for ``u`` and ``v`` components |
+------------------------------------------------+-------+-------------------------------------------------------------+
| ``direction(u, v)`` or ``dd(u, v)`` or | ``2`` | Returns wind direction for ``u`` and ``v`` components |
| ``dir(u, v)`` | | |
+------------------------------------------------+-------+-------------------------------------------------------------+
.. _`aggregate-functions`:
Aggregate Functions
~~~~~~~~~~~~~~~~~~~
Aggregate functions return a single value, calculated from values an expression passed as parameter to the function evaluates to for selected rows.
+---------------------------+-------+----------------------------------------------------------------------------------+
| Function | Arity | Description |
+===========================+=======+==================================================================================+
| ``dotp(x, y)`` | ``2`` | Compute dot product of ``x`` and ``y`` |
+---------------------------+-------+----------------------------------------------------------------------------------+
| ``rms(x)`` | ``1`` | Compute Root Mean Square of ``x`` |
+---------------------------+-------+----------------------------------------------------------------------------------+
| ``stdev(x)`` | ``1`` | Compute standard deviation |
+---------------------------+-------+----------------------------------------------------------------------------------+
| ``norm(x, y)`` | ``2`` | Compute the norm of ``x`` and ``y`` |
+---------------------------+-------+----------------------------------------------------------------------------------+
| ``var(x)`` or ``varp(x)`` | ``1`` | Compute variance |
+---------------------------+-------+----------------------------------------------------------------------------------+
| ``avg(x)`` | ``1`` | Returns average value |
+---------------------------+-------+----------------------------------------------------------------------------------+
| ``max(x)`` | ``1`` | Returns largest value |
+---------------------------+-------+----------------------------------------------------------------------------------+
| ``count(x)`` | ``1`` | Returns number of rows |
+---------------------------+-------+----------------------------------------------------------------------------------+
| ``min(x)`` | ``1`` | Returns smallest value |
+---------------------------+-------+----------------------------------------------------------------------------------+
| ``sum(x)`` | ``1`` | Returns sum |
+---------------------------+-------+----------------------------------------------------------------------------------+
| ``first(x)`` | ``1`` | Returns value of the given expression evaluated for the first row of the query’s |
| | | result set |
+---------------------------+-------+----------------------------------------------------------------------------------+
| ``last(x)`` | ``1`` | Returns value of the given expression evaluated for the last row of the query’s |
| | | result set |
+---------------------------+-------+----------------------------------------------------------------------------------+
Data Types
----------
The columns in ODB-2 files can currently be one of :ref:`the following data types <column-type>`.
The actual type of a column can be found using :ref:`odc header <odc-header>` tool.
Bitfields
---------
Bitfields allow for naming and accessing sequences of bits in a column.
Referring to Bitfield Members
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Syntax for accessing a member of a bitfield is:
.. code-block:: none
<column-name>.<bitfield-member-name>
In case it is necessary to specify table name when referring to a column, correct way of referring to a member is:
.. code-block:: none
<column-name>.<bitfield-member-name>@<table-name>
For example:
.. code-block:: none
report_status.active@hdr
Expanding List of Members
~~~~~~~~~~~~~~~~~~~~~~~~~
The list of bitfield members can be expanded with the asterisk (``*``) operator.
For example:
.. code-block:: none
report_status.*@hdr
will be expanded to:
.. code-block:: none
report_status.active@hdr, report_status.passive@hdr, report_status.rejected@hdr, report_status.blacklisted@hdr, report_status.use_emiskf_only@hdr
Finding Details of Bitfield Definition
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The :ref:`odc header <odc-header>` tool can be used to find out details of bitfield definition: its members and number of bits they occupy.
Examples
--------
Unique station identifiers
Which station identifiers are in the ODB-2 file?
.. code-block:: shell
odc sql -i example.odb 'select distinct statid'
statid@hdr
' 96413'
' 27707'
' 27730'
' 27962'
' 27995'
' 34009'
' 34172'
Row limit
How to display first 10 rows from an ODB-2 file?
.. code-block:: shell
odc sql -i example.odb 'select date, lat, lon, obsvalue where rownumber() < 10'
date@hdr lat@hdr lon@hdr obsvalue@body
20210618 1.480000 110.330002 260.000000
20210618 1.480000 110.330002 296.399994
20210618 1.480000 110.330002 295.600006
20210618 1.480000 110.330002 0.952672
20210618 1.480000 110.330002 0.016915
20210618 1.480000 110.330002 50.000000
20210618 1.480000 110.330002 1.000000
20210618 1.480000 110.330002 -0.766044
20210618 1.480000 110.330002 -0.642788
Geophysical variables
What geophysical variables are in the ODB-2 file?
.. code-block:: shell
odc sql -i example.odb 'select distinct varno'
varno@body
1
39
40
58
7
111
112
41
42
2
59
29
3
4
See `ODB Governance`_ for description of numeric values of ``varno``. For example:
+-----------+---------------------------+
| ``varno`` | Description |
+===========+===========================+
| ``1`` | Geopotential |
+-----------+---------------------------+
| ``2`` | Upper air temperature |
+-----------+---------------------------+
| ``3`` | Upper air meridional wind |
+-----------+---------------------------+
| ``4`` | Upper air zonal wind |
+-----------+---------------------------+
| ``7`` | Specific humidity |
+-----------+---------------------------+
| ``29`` | Upper air rel. humidity |
+-----------+---------------------------+
| ``39`` | 2m temperature |
+-----------+---------------------------+
| ``40`` | 2m dew point |
+-----------+---------------------------+
| ``41`` | 10m meridional component |
+-----------+---------------------------+
| ``42`` | 10m zonal component |
+-----------+---------------------------+
| ``58`` | 2m relative humidity |
+-----------+---------------------------+
| ``59`` | Upper air dew point |
+-----------+---------------------------+
| ``111`` | Wind direction |
+-----------+---------------------------+
| ``112`` | Wind speed |
+-----------+---------------------------+
Number of temperature records
Count the number of temperature records.
.. code-block:: shell
odc sql -i example.odb 'select count(*) where varno=2'
count(1)
448.000000
``count(*)`` is an :ref:`aggregation function <aggregate-functions>`. Based on the other keys present in the SQL query (here: filtering to select only the temperature entries), each population of identified entries see the data subjected to the aggregation function.
Number of temperature records per station identifier
Count the number of temperature records, this time per station identifier, where the observation values are not missing.
.. code-block:: shell
odc sql -i example.odb 'select count(*), statid where varno=2 and obsvalue is not null'
count(1) statid@hdr
39.000000 ' 27707'
49.000000 ' 27730'
37.000000 ' 27962'
44.000000 ' 27995'
38.000000 ' 34009'
9.000000 ' 34172'
50.000000 ' 96413'
Group records by several columns at the same time
Count the number of temperature records, per station identifier and date, and display the average observed value as a separate column.
.. code-block:: shell
odc sql -i example.odb 'select count(*), avg(obsvalue), statid, date where varno=2 and obsvalue is not null'
count(1) avg(obsvalue) statid@hdr date@hdr
39.000000 243.792309 ' 27707' 20210618
49.000000 243.603535 ' 27730' 20210618
37.000000 241.151352 ' 27962' 20210618
44.000000 246.002271 ' 27995' 20210618
38.000000 245.532427 ' 34009' 20210618
9.000000 287.548445 ' 34172' 20210618
50.000000 233.472708 ' 96413' 20210618
For each set of non-aggregated rows an independent aggregate variable is kept. The returned result is exactly the same as for the following statement:
.. code-block:: shell
odc sql -i example.odb 'select count(*), avg(obsvalue), statid, date where varno=2 and obsvalue is not null group by statid, date'
000 2021-06-28 14:28:18 (I) GROUP BY clause seen and ignored. Non aggregated values on select list will be used instead.
count(1) avg(obsvalue) statid@hdr date@hdr
39.000000 243.792309 ' 27707' 20210618
49.000000 243.603535 ' 27730' 20210618
37.000000 241.151352 ' 27962' 20210618
44.000000 246.002271 ' 27995' 20210618
38.000000 245.532427 ' 34009' 20210618
9.000000 287.548445 ' 34172' 20210618
50.000000 233.472708 ' 96413' 20210618
Average temperature at 100 hPa
Get the observation count at one station and average temperature observation value by pressure level bins of 100 hPa each, showing also the average pressure in each pressure bin.
.. code-block:: shell
odc sql -i example.odb 'select count(*), avg(fg_depar), floor(vertco_reference_1/10000.0), avg(vertco_reference_1/100.0) where varno=2 and statid="27707" and fg_depar is not null'
count(1) avg(fg_depar) floor(/(vertco_reference_1,10000)) avg(/(vertco_reference_1,100))
11.000000 0.505271 0 43.318182
5.000000 -0.160176 1 120.600000
5.000000 -0.227211 2 218.400000
2.000000 1.077009 3 316.500000
3.000000 0.370587 4 438.666667
3.000000 0.385093 5 553.666667
1.000000 0.324625 6 637.000000
1.000000 -0.013323 7 700.000000
4.000000 0.635424 8 836.000000
4.000000 0.118218 9 932.500000
Meridional and zonal wind near 500 hPa
Get the observation count at one station and mean observation minus first-guess departure for meridional wind and zonal wind near 500 hPa.
.. code-block:: shell
odc sql -i example.odb 'select count(*), avg(fg_depar) where varno in (3,4) and statid="27707" and vertco_reference_1>=45000. and vertco_reference_1<55000. and fg_depar is not null'
count(1) avg(fg_depar)
4.000000 -0.238838
.. _`SQL (Structured Query Language)`: https://en.wikipedia.org/wiki/SQL
.. _`ODB Governance`: http://apps.ecmwf.int/odbgov/varno/
|
