How to implement generic Oracle DECODE function in BigQuery? - google-bigquery

Question

I'm looking into implementing the Oracle DECODE function as a UDF.
Below is the outward functionaliy
https://docs.oracle.com/cd/B19306_01/server.102/b14200/functions040.htm
Below is the outward functionality and syntax of a decode in Oracle:
Oracle:
DECODE( <expr> , <search1> , <result1> [ , <search2> , <result2> ... ] [ , <default> ] )
SELECT product_id,
DECODE (warehouse_id, 1, 'Southlake',
2, 'San Francisco',
3, 'New Jersey',
4, 'Seattle',
'Non domestic')
"Location of inventory" FROM inventories;
Primarily, with BigQuery UDFs SQL or JavaScript, with BigQuery UDFs, when you define the UDF function you need to know the number of parameters you are accepting and typing. When you define the SQL UDF function, you can also accept an array of type anything, but I am not sure if it can work and SQL UDF can perform what we want with an array. It seems based on the Javascript UDF documentation all parameters are named and typed and known up front.
Is there a way to accomplish this using a BigQuery UDF, it has to be dynamic like Oracle decode and fit any scenario you put in front of it not static knowing what you are decoding

Answer 1

Below is for BigQuery Standard SQL
CREATE TEMP FUNCTION DECODE(expr ANY TYPE, map ANY TYPE, `default` ANY TYPE ) AS ((
IFNULL((SELECT result FROM UNNEST(map) WHERE search = expr), `default`)
));
You can see how it works using below example
#standardSQL
CREATE TEMP FUNCTION DECODE(expr ANY TYPE, map ANY TYPE, `default` ANY TYPE ) AS ((
IFNULL((SELECT result FROM UNNEST(map) WHERE search = expr), `default`)
));
WITH `project.dataset.inventories` AS (
SELECT 1 product_id, 4 warehouse_id UNION ALL
SELECT 2, 2 UNION ALL
SELECT 3, 5
)
SELECT product_id, warehouse_id,
DECODE(warehouse_id,
[STRUCT<search INT64, result STRING>
(1,'Southlake'),
(2,'San Francisco'),
(3,'New Jersey'),
(4,'Seattle')
], 'Non domestic') AS `Location_of_inventory`
FROM `project.dataset.inventories`
with result
Row product_id warehouse_id Location_of_inventory
1 1 4 Seattle
2 2 2 San Francisco
3 3 5 Non domestic
Another example of use is:
#standardSQL
CREATE TEMP FUNCTION DECODE(expr ANY TYPE, map ANY TYPE, `default` ANY TYPE ) AS ((
IFNULL((SELECT result FROM UNNEST(map) WHERE search = expr), `default`)
));
WITH `project.dataset.inventories` AS (
SELECT 1 product_id, 4 warehouse_id UNION ALL
SELECT 2, 2 UNION ALL
SELECT 3, 5
), map AS (
SELECT 1 search, 'Southlake' result UNION ALL
SELECT 2, 'San Francisco' UNION ALL
SELECT 3, 'New Jersey' UNION ALL
SELECT 4, 'Seattle'
)
SELECT product_id, warehouse_id,
DECODE(warehouse_id, kv, 'Non domestic') AS `Location_of_inventory`
FROM `project.dataset.inventories`,
(SELECT ARRAY_AGG(STRUCT(search, result)) AS kv FROM map) arr
with the same output
Update to address - "for a reusable UDF, not having to name the fields makes it closer to Oracle's implementation."
CREATE TEMP FUNCTION DECODE(expr ANY TYPE, map ANY TYPE, `default` ANY TYPE ) AS (
IFNULL((
SELECT result FROM (
SELECT NULL AS search, NULL AS result UNION ALL SELECT * FROM UNNEST(map)
)
WHERE search = expr
), `default`)
);
So now - previous examples can be used w/o explicit naming fields as in example below
#standardSQL
CREATE TEMP FUNCTION DECODE(expr ANY TYPE, map ANY TYPE, `default` ANY TYPE ) AS (
IFNULL((
SELECT result FROM (
SELECT NULL AS search, NULL AS result UNION ALL SELECT * FROM UNNEST(map)
)
WHERE search = expr
), `default`)
);
WITH `project.dataset.inventories` AS (
SELECT 1 product_id, 4 warehouse_id UNION ALL
SELECT 2, 2 UNION ALL
SELECT 3, 5
)
SELECT product_id, warehouse_id,
DECODE(warehouse_id,
[ (1,'Southlake'),
(2,'San Francisco'),
(3,'New Jersey'),
(4,'Seattle')
], 'Non domestic') AS `Location_of_inventory`
FROM `project.dataset.inventories`
still with same output as before

Answer 2

```
SELECT product_id,
case
when warehouse_id = 1 then 'Southlake'
when warehouse_id = 2 then 'San Francisco'
when warehouse_id = 3 then 'New Jersey'
when warehouse_id = 4 then 'Seattle'
else
'Non domestic'
end as "Location of inventory" FROM inventories;
```