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BUG: Chained mutate operations give wrong results #1799

ayushi04 opened this issue May 27, 2019 · 0 comments


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commented May 27, 2019

Mutate function is giving wrong output. Please check below sample example.

table_expr = ibis.table([('a', 'string'), ('b', 'string')]) 
table_expr1 = table_expr['b'].fillna('Short Term') 
table_expr = table_expr.mutate(b = table_expr1) 
table_expr2 = table_expr['a'].fillna('Short Term') 
table_expr = table_expr.mutate(a = table_expr2) 

For the above program output is :
SELECT isnull(a, 'Short Term') AS a, b FROM t0

instead of
SELECT isnull(a, 'Short Term') AS a, isnull(b, 'Short Term') AS b FROM t0

Let me know if anything is wrong in my understanding.

@cpcloud cpcloud added this to the 1.1.0 milestone May 31, 2019

@cpcloud cpcloud self-assigned this May 31, 2019

@cpcloud cpcloud changed the title mutate function is not working correctly BUG: Chained mutate operations give wrong results Jun 1, 2019

@cpcloud cpcloud closed this in #1812 Jun 7, 2019

cpcloud added a commit that referenced this issue Jun 7, 2019

BUG: Chained mutate operations give wrong results
Closes #1799    This was kind of a nasty one. The query flattening
optimization was far too  aggressive.    @toryhaavik Do you feel
comfortable reviewing this?    One downside to this fix is that
simple, single expression columns are not flattened into their
subquery anymore. This will be addressed in the future after the
compiler is refactored.
Author: Phillip Cloud <>

Closes #1812 from cpcloud/mutate-chain-bug and squashes the following commits:

31dedd6 [Phillip Cloud] BUG: Chained mutate operations give wrong results
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