Add execute_sql function to enable execution of SQL code where no DataFrame is returned

[madhav-datt]

Initial pull request based on the discussion and issue explained here. I'd love to discuss any changes to the design of this function, or if it might be better to add this functionality elsewhere.

[codecov-io]

Codecov Report

Merging #90 into master will decrease coverage by 45.46%.
The diff coverage is 20%.

@@             Coverage Diff             @@
##           master      #90       +/-   ##
===========================================
- Coverage   73.44%   27.98%   -45.47%     
===========================================
  Files           4        4               
  Lines        1578     1583        +5     
===========================================
- Hits         1159      443      -716     
- Misses        419     1140      +721

Impacted Files	Coverage Δ
pandas_gbq/gbq.py	19.35% <20%> (-56.96%)	⬇️
pandas_gbq/tests/test_gbq.py	27.76% <0%> (-54.18%)	⬇️

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[max-sixty]

I think it's mostly coincidental that the existing function raises a KeyError. Can we find a more coherent way of doing this?

[tswast]

Could you rebase this PR on the latest version in master? There have been some significant changes since this was opened. We changed what library we use to actually make the API calls to BigQuery.

[madhav-datt]

@tswast Thanks so much for the update. I'll change this PR based on the latest code in master.

[max-sixty]

@madhav-datt Would love to merge this. Let us know if you're up for updating this.

[tswast]

I've been thinking about this in regards to dryRun queries, too. (#88) I think it might make some sense for read_gbq to return an empty dataframe in the case when there are no result rows.

[madhav-datt]

Thanks for the follow up! Sure - I'll go ahead and update the pull request.

[max-sixty]

@madhav-datt this is v close! How would you feel about pushing over the line?

[tswast]

Thank you for the contribution @madhav-datt and your patience. I'm closing this in favor of #286 which adds a max_results argument to read_gbq. Set max_results=0 if no results are desired.