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Advanced Functions

Watsonx.data supports several types of functions including:

  • Mathematical functions
  • Conversion functions
  • String functions
  • Regular expression functions
  • Window functions
  • URL functions
  • Geospatial functions

For a complete list see - https://prestodb.io/docs/current/functions.html. We will look at using a few simple examples as part of this lab.

Switch to the bin directory.

cd /root/ibm-lh-dev/bin

Connect to the Workshop Schema.

./presto-cli --catalog iceberg_data --schema workshop

Concatenation of one or more string/varchar values

Note: We are using a combination of the “concat” string function and the “cast” conversion function as part of this query.

select 
   concat(cast(custkey as varchar),'--',name) 
from 
   customer
limit 2;

          _col0          
-------------------------
 376--Customer#000000376 
 377--Customer#000000377 
(2 rows)

Date functions

Date functions can be used as part of the projected columns or in the predicate/where clause. Select orders from the last 2 days.

select
   orderdate 
from 
   orders 
where 
   orderdate >  date '1998-08-02' - interval '2' day;

 orderdate  
------------
 1998-08-02 
 1998-08-02 
 1998-08-01 
 1998-08-01 
 1998-08-02 
 1998-08-01 
 1998-08-01 
 1998-08-01 
 1998-08-02 
 1998-08-02 
 1998-08-02 
 1998-08-02 
(12 rows)

Number of orders by year.

select 
   distinct year(orderdate), count(orderkey) 
from 
   orders 
group by 
   year(orderdate);

 _col0 | _col1 
-------+-------
  1993 |  2307 
  1994 |  2303 
  1998 |  1346 
  1996 |  2297 
  1995 |  2204 
  1992 |  2256 
  1997 |  2287 
(7 rows)

Geospatial functions

There are 3 basic geometries, then some complex geometries. The basic geometries include:

  • Points
  • Lines
  • Polygons

Points

You could use https://www.latlong.net to get the longitude/latitude given any address.

select 
   ST_Point(-121.748360,37.195840) as SVL, 
   ST_Point(-122.378952, 37.621311) as SFO;

             SVL             |              SFO              
-----------------------------+-------------------------------
 POINT (-121.74836 37.19584) | POINT (-122.378952 37.621311) 
(1 row)

Lines

You could use https://www.latlong.net to get the longitude/latitude for 2 points and then create a straight line from it. Below is just a small stretch of the road leading to IBM SVL campus.

select 
   ST_LineFromText('LINESTRING (-121.74294303079807 37.19665657093434, -121.73659072815602 37.20102399761407)');

                                           _col0                                           
-------------------------------------------------------------------------------------------
 LINESTRING (-121.74294303079807 37.19665657093434, -121.73659072815602 37.20102399761407) 
(1 row)

Polygons

You could use https://geojson.io/#map=16.39/37.196336/-121.746303 to click around and generate the coordinates for a polygon of any shape. The following is a polygon of the IBM Silicon Valley campus.

select ST_Polygon('POLYGON (
   (-121.74418635253568 37.196001834113844, 
    -121.74499684288966 37.19668005184322,
    -121.74584008032835 37.19707784979194,  
    -121.74629035274705 37.197645197338105, 
    -121.74672425162339 37.198186455965086, 
    -121.74705172247337 37.19828427337538, 
    -121.74760023614738 37.19827775221884,  
    -121.74848440744239 37.19836252721197, 
    -121.74932764488139 37.19789300297414,  
    -121.75039192514376 37.19746260319114, 
    -121.75130884352407 37.19721479614175, 
    -121.75195559845278 37.1963670290329, 
    -121.75198015876644 37.19555185937345,  
    -121.7508585711051 37.19458016564036, 
    -121.74940132582242 37.19447582194559,  
    -121.74841891327239 37.1942866986312,
    -121.7474446874937 37.193556286900346, 
    -121.74418635253568 37.196001834113844))');

Truncated output
------------------------------------------------------------------------------------------------------------------------------------------------------>
 POLYGON ((-121.74418635253568 37.196001834113844, -121.74499684288966 37.19668005184322, -121.74584008032835 37.19707784979194, -121.74629035274705 3>
(1 row)

So now that we have 3 basic geometries Point, Line and Polygon we can perform different operations on spatial data including:

  • Distance between 2 points
  • Point in polygon
  • Intersection of line and polygon   Distance between SFO airport and IBM SVL

We can now use geospatial functions in a nested way to find the distance between 2 points.

select 
   ST_Distance(to_spherical_geography(ST_Point(-122.378952, 37.621311)), 
   to_spherical_geography(ST_Point(-121.748360,37.195840)))*0.000621371 as distance_in_miles;

distance_in_miles  
--------------------
 45.408431373195654 
(1 row)

Exit Presto.

quit;