python regex fetching column details from ddl - regex

Question

USE test_db2
CREATE TABLE test_table2
(
Subscn_Purch_Id BIGINT COMMENT 'from deserializer',
Price_Amt DECIMAL(38,18),
Purch_Line_Item_Id BIGINT,
Subscn_Purch_Status_Id BIGINT COMMENT 'from defdf',
Offer_Coupon_Id BIGINT, -- INTRO OFFER
Offer_Period_Hrs BIGINT,
discount_offer_id STRING -- DISCOUNT
)
PARTITIONED BY (
testcol bigint
)
ROW FORMAT SERDE
'eeee'
STORED AS INPUTFORMAT
'rrrr'
OUTPUTFORMAT
'tttt';
from the above DDL I need to get the column level details.
ie,
column name,
data type,
data length (if any present)
data precision (if any present)
column comment (if any present)
I don't need the comment details like '-- INTRO OFFER' and '-- DISCOUNT' in the above sample.
I have tried using the regex
\s*(\w+)\s*(\w+)(?:\s*\,\s*)?(?:\((\d+)(?:,\s?(\d+))?\))?(?:\s*\,\s*)?(?:(?=(?:.*COMMENT\s*)\'(.*)\'(?:\,|\))))
this regex is fetching the details that have 'COMEMNT' word In it but not the others.on adding '?' at the end of this regex ,its fetching the details which I son't need.
how to achieve this.
attaching the regex101 link :
https://regex101.com/r/QfOCfj/3

Answer 1

The regex by #Jan might get you what you want, but there is potentially a much cleaner way to go about this. You may try just querying the information schema tables directly in DB2.
SELECT
COLNO,
SYSTEM_COLUMN_NAME,
DATA_TYPE,
COALESCE(PRECISION, LENGTH) AS length,
SMALLINT(SCALE) AS scale,
STORAGE
FROM QSYS2/SYSCOLUMNS
WHERE
SYSTEM_TABLE_SCHEMA = 'your_db' AND
SYSTEM_TABLE_NAME = 'test_table2';

Answer 2

Generally, it is usually not a good idea to try to parse these strings with regular expressions. That being said, you could try to use the newer regex module which supports \G:
(?:\G(?!\A)|\()
\s*
(?P<column_name>\w+)\s+
(?P<column_type>\w+)
(?:
\(
(?P<column_size>[^()]+)
\)
)?
[, ]+
.*
See a demo on regex101.com and mind the modifiers.
Alternatively - if installing another module is not an option - use two expressions:
Fetch every block of ( and ) first recursively
Analyze that block with the above expression minus the first line