getredash/redash

When column type is STRING and one of the values is NULL, values get cast to strings

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#2074 opened on Nov 6, 2017

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 (23 comments) (0 reactions) (0 assignees)Python (24,845 stars) (4,236 forks)batch import
BugFrontendhelp wanted

Description

Query to reproduce:

select '2016-04-09' as t
union all
select null as t

http://demo.redash.io/queries/5638/source

Contributor guide

Tech stack
pythonsql
Domain
backenddata
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
SQL basicsPython debugging
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
45
Research direction
The issue reproduces a bug where NULL values in a STRING column are incorrectly cast as strings. Start by examining how Redash handles type inference in query results, particularly in the query runner or result serializer. Look at the code that processes UNION queries and the handling of NULL values. The provided demo link may help understand the output.