Spark SQL相关总结

1.spark 数据透视图：

pivot(pivot_col, values=None)

Pivots a column of the current [[DataFrame]] and perform the specified aggregation. There are two versions of pivot function: one that requires the caller to specify the list of distinct values to pivot on, and one that does not. The latter is more concise but less efficient, because Spark needs to first compute the list of distinct values internally.

Parameters:	pivot_col – Name of the column to pivot. values – List of values that will be translated to columns in the output DataFrame.

# Compute the sum of earnings for each year by course with each course as a separate column

>>> df4.groupBy("year").pivot("course", ["dotNET", "Java"]).sum("earnings").collect()
[Row(year=2012, dotNET=15000, Java=20000), Row(year=2013, dotNET=48000, Java=30000)]

# Or without specifying column values (less efficient)

>>> df4.groupBy("year").pivot("course").sum("earnings").collect()
[Row(year=2012, Java=20000, dotNET=15000), Row(year=2013, Java=30000, dotNET=48000)]