Revisit Impala's CASE expression type precedence rules

[wesm]

Issue by wesm
Friday Jan 30, 2015 at 22:37 GMT
Originally opened as http://github.mtv.cloudera.com/wesm/ibis/issues/93

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see #31

[cpcloud]

The postgres algorithm for deciding the output type looks reasonable here: https://www.postgresql.org/docs/current/static/typeconv-union-case.html

[kszucs]

@cpcloud This issue seems a bit outdated, should we still revisit?

[cpcloud]

This is really a backlog issue, that we may or may not get to after other higher priority issues are done. We can still leave it open though.

[xmnlab]

Hi all,

I am trying the follow code but it raises an error: IbisTypeError: Cannot compute precedence for int32 and string types

t0 = ibis.table(
    [('one', 'string'),
     ('two', 'double'),
     ('three', 'int32')], 'my_data')

expr = (
    t0.three
        .case()
        .when(0, 'low')
        .when(1, 'high')
        .else_('null')
        .end()
        .name('label')
)

print(t0[expr].limit(10).compile())

How can I allow this? I need it because I am creating a backend and it allow this kind of operation.

[cpcloud]

@xmnlab This looks like a bug since the types you've written in your example are perfectly valid.

[cpcloud]

I'm going to move your example to a separate issue.

[cpcloud]

Closing as stale.