Preserve order in to_dataframe with BQ Storage from queries containing ORDER BY
#7793
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googlebot
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cla: yes
tswast
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api: bigquery
shollyman
approved these changes
Apr 26, 2019
| if query is None: | ||
| return False | ||
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| return re.search(r"ORDER\s+BY", query, re.IGNORECASE) is not None |
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Should we have a comment indicating we know there's a class of false positives (ordered window functions)?
tseaver
suggested changes
Apr 29, 2019
| if query is None: | ||
| return False | ||
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| return re.search(r"ORDER\s+BY", query, re.IGNORECASE) is not None |
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Please compile the pattern as a module-scope global, and use "raw" strings e.g.:
_CONTAINS_ORDER_BY = re.compile(r"ORDER\s+BY", re.IGNORECASE)
...
def _contains_order_by(query):
"""Do we need to preserve the order of the query results?"""
return query and _CONTAINS_ORDER_BY.search(query)
…ng ORDER BY This fixes an issue where due to reading from multiple stream in parallel, the order of rows is not preserved. Normally this isn't an issue, but it is when the rows are query results from an ORDER BY query.
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tseaver
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Apr 30, 2019
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This fixes an issue where due to reading from multiple stream in
parallel, the order of rows is not preserved. Normally this isn't an
issue, but it is when the rows are query results from an
ORDER BYquery.Note: The detection of
ORDER BYis not perfect. It will have false positives (such asORDER BYin a string or sub-query), but hopefully no false negatives. Since a false positive only means we read from a single stream, behavior is correct but perhaps slower than expected.Closes #7759