Tutorial by Topics: groupby



Results of a SELECT query can be grouped by one or more columns using the GROUP BY statement: all results with the same value in the grouped columns are aggregated together. This generates a table of partial results, instead of one result. GROUP BY can be used in conjunction with aggregation functions using the HAVING statement to define how non-grouped columns are aggregated.

Recently, new versions of MySQL servers have begun to generate 1055 errors for queries that used to work. This topic explains those errors. The MySQL team has been working to retire the nonstandard extension to GROUP BY, or at least to make it harder for query writing developers to be burned by it.

In Python, the itertools.groupby() method allows developers to group values of an iterable class based on a specified property into another iterable set of values.


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