Is it possible to parse json by using select statement in Netezza? - netezza

Question

I have json data in one of the column of my table and I would like to parse json data by using select statement in Netezza. I am not able to figure it out.
Can you all help me to solve this problem?
Let's say I have TableA and this table has column Customer_detail. data from customer_detail field lookss like this
'{"Customer":[{"id":"1","name":"mike","address":"NYC"}]}'
Now I would like to query id from customer object of customer_detail column.
Thanks in advance.

Answer 1

From NPS 11.1.0.0 onwards, you can parse and use json datatype itself in NPS.
Here's an example
SYSTEM.ADMIN(ADMIN)=> create table jtest(c1 jsonb);
CREATE TABLE
SYSTEM.ADMIN(ADMIN)=> insert into jtest values('{"name": "Joe Smith", "age": 28, "sports": ["football", "volleyball", "soccer"]}');
INSERT 0 1
SYSTEM.ADMIN(ADMIN)=> insert into jtest values('{"name": "Jane Smith", "age": 38, "sports": ["volleyball", "soccer"]}');
INSERT 0 1
SYSTEM.ADMIN(ADMIN)=> select * from jtest;
C1
----------------------------------------------------------------------------------
{"age": 28, "name": "Joe Smith", "sports": ["football", "volleyball", "soccer"]}
{"age": 38, "name": "Jane Smith", "sports": ["volleyball", "soccer"]}
(2 rows)
SYSTEM.ADMIN(ADMIN)=> select c1 -> 'name' from jtest where c1 -> 'age' > 20::jsonb ;
?COLUMN?
--------------
"Joe Smith"
"Jane Smith"
(2 rows)
You can refer to https://www.ibm.com/support/knowledgecenter/SSTNZ3/com.ibm.ips.doc/postgresql/dbuser/r_dbuser_functions_expressions.html for more details as well.
Looking at the comment you put above, something like
select customer_detail::json -> 'Customer' -> 0 -> 'id' as id,
customer_detail::json -> 'Customer' -> 0 -> 'name' as name
from ...
This will parse the text to json during every execution. A more performant would be to convert customer_detail to jsonb datatype
If the NPS version is below 11.1.x then the json handling needs to be done (a) externally as in using sql to get the json data and then processing it outside the database or (b) using UDF - creating a UDF that supports json parsing
E.g -
Using the programming language of choice, process the json external to SQL
import nzpy # install using "python3 -m pip install nzpy"
import os
import json
# assume NZ_USER, NZ_PASSWORD, NZ_DATABASE and NZ_HOST are set
con = nzpy.connect(user=os.environ["NZ_USER"],
password=os.environ["NZ_PASSWORD"], host=os.environ["NZ_HOST"],
database=os.environ["NZ_DATABASE"], port=5480)
with con.cursor() as cur:
cur.execute('select customer_detail from ...')
for customer_detail in cur.fetch_all():
c = json.loads(customer_detail)
print((c['Customer'][0]['name'], c['Customer'][0]['id']))
Or create a UDF that parses json and use that in the SQL query
If none of those are options, and the json is always well formatted (ie. no new lines, only one key called "id" and one key called "name", etc) then a regex may be a way around, though its not recommended since its not a real json parser
select regexp_extract(customer_detail,
'"id"[[:space:]]*:[[:space:]]*"([^"]+)"', 1, 1) as id,
regexp_extract(customer_detail,
'"name"[[:space:]]*:[[:space:]]*"([^"]+)"', 1, 1) as name
....