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# spark

很多代码来自 [Spark权威指南](https://github.com/databricks/Spark-The-Definitive-Guide)

## pyspark使用ipython3

```
    export PYSPARK_DRIVER_PYTHON=ipython3
```

## explain 查看执行命令，类似mysql

```
    In [1]: df = spark.range(10).toDF("N")

    In [2]: df.explain()
    == Physical Plan ==
    *(1) Project [id#0L AS N#2L]
    +- *(1) Range (0, 10, step=1, splits=8)
```

## 取某列的最大值

```
    from pyspark.sql.functions import max

    flightData2015.select(max("count")).take(1)
```

## group by 并求和

```
maxSql = spark.sql("""
SELECT DEST_COUNTRY_NAME, sum(count) as destination_total
FROM flight_data_2015
GROUP BY DEST_COUNTRY_NAME
ORDER BY sum(count) DESC
LIMIT 5
""")

maxSql.show()


    from pyspark.sql.functions import desc

    flightData2015\
        .groupBy("DEST_COUNTRY_NAME")\
        .sum("count")\
        .withColumnRenamed("sum(count)", "destination_total")\
        .sort(desc("destination_total"))\
        .limit(5)\
        .show()
```


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