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Hive QL Spark SQL - Transform Rows into Columns

 

For a Structured Tabular Structure it is many a times required to transform Rows into Columns. This blog explains step by step process which can be executed as one SQL to achieve same. 

Lets try to understand with help of below example: where -in , we want to implement / transform input Table into table structure mentioned as output.


INPUT_TABLE 

topic
groupId
batchTimeMs
Partition 
offset 
Count 
t1 g001 1658173779 0123 122
t1g001 1658173779 12231100
t2g001 1658173779 01211

OUTPUT_TABLE 

rowkey:key

offset:0

count:0    

offset:1 

count:1 

t1:g001:1658173779 1231222231100

t2:g001:1658173779 

1211NULLNULL

 



FIRST STEP -

  • Concat Topic, GroupID, and BatchTimeMS to create RowKey 
  • Create Columns - offsets:0, counts:0, offsets:1, counts:1. Such that Columns has value only when respective partition value matches with column name.
  • SQL as below -

select concat_ws(':', topic,groupId,batchTimeMs) as rowkey,

case when partition='0' then offset else null end as `offsets:0`,

case when partition='0' then count else null end as `counts:0`,

case when partition='1' then offset else null end as `offsets:1`,

case when partition='1' then count else null end as `counts:1`

FROM INPUT_TABLE



rowkey

offset:0

count:0    

offset:1 

count:1 

t1:g001:1658173779 123122NULLNULL
t1:g001:1658173779NULLNULL2231100

t2:g001:1658173779 

1211NULLNULL




SECOND STEP-

  • Bring in all values of a ROWKEY in to one row. 
  • SQL as below -
select rowkey as `rowkey:key`,
collect_set(`offsets:0`)  as `offsets:0`,
collect_set(`counts:0`)  as `counts:0`,
collect_set(`offsets:1`)  as `offsets:1`,
collect_set(`counts:1`)  as `counts:1` FROM (
select concat_ws(':', topic,groupId,batchTimeMs) as rowkey,
case when partition='0' then offset else null end as `offsets:0`,
case when partition='0' then count else null end as `counts:0`,
case when partition='1' then offset else null end as `offsets:1`,
case when partition='1' then count else null end as `counts:1`
FROM INPUT_TABLE ) T1 group by rowkey

rowkey:key

offset:0

count:0    

offset:1 

count:1 

t1:g001:1658173779 [123, NULL][122, NULL][2231,NULL][100,NULL]

t2:g001:1658173779 

[12][11][NULL][NULL]



THIRD STEP - 
  • Select only first value from Array of values.
  • SQL as below resulting in final desired output - 
select rowkey as `rowkey:key`,
collect_set(`offsets:0`) [0] as `offsets:0`,
collect_set(`counts:0`) [0] as `counts:0`,
collect_set(`offsets:1`) [0] as `offsets:1`,
collect_set(`counts:1`) [0] as `counts:1` FROM (
select concat_ws(':', topic,groupId,batchTimeMs) as rowkey,
case when partition='0' then offset else null end as `offsets:0`,
case when partition='0' then count else null end as `counts:0`,
case when partition='1' then offset else null end as `offsets:1`,
case when partition='1' then count else null end as `counts:1`
FROM INPUT_TABLE ) T1 group by rowkey

rowkey:key

offset:0

count:0    

offset:1 

count:1 

t1:g001:1658173779 1231222231100

t2:g001:1658173779 

1211NULLNULL

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