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Hive SQL: Multi column explode, Creating Map from Array & Rows to Column

By Dinesh

 Say, you have a Table like below - 

A

[K1, K2, K3]

[V1,V2,V3]

B

[K2]

[V2]

C

[K1,K2,K3,K4,K5]

[V1,V2,V3,V4,V5]

 

And you want a final table like below :

 

K1

K2

K3

K4

K5

A

V1

V2

V3

 

 

B

 

V2

 

 

 

C

V1

V2

V3

V4

V5

It Can be done with SQL - 

select id, arrMap['K1'] K1, arrMap['K2'] K2, arrMap['K3'] K3, arrMap['K4'] K4, arrMap['K5'] K5, from (select id, str_to_map(concat_ws(',', (collect_list(kv)))) arrMap from (select id, n.pos, concat_ws(':', n.attribute, value[n.pos]) kv from  INPUT_TABLE lateral view posexplode(attributes) n as pos, attribute )T group by id) T1;


Explanation:

1) Inner query explodes multiple columns and does a 1-to-1 mapping instead of 1-to-many mapping 

select id, n.pos, concat_ws(':', n.attribute, value[n.pos]) kv from  INPUT_TABLE lateral view posexplode(attributes) n as pos, attribute 

A

K1:V1

A

K2:V2

A

K3:V3

B

K2:V2

C

K1:V1

C

K2:V2

C

K3:V3

C

K4:V4

C

K5:V5


2) Then we convert multiple rows with same key into one row and value as a Map for all key value.

select id, str_to_map(concat_ws(',', (collect_list(kv)))) arrMap from (select id, n.pos, concat_ws(':', n.attribute, value[n.pos]) kv from  INPUT_TABLE lateral view posexplode(attributes) n as pos, attribute )T group by id

A

{K1:V1, K2:V2, K3:V3}

B

{K2:V2}

C

{K1:V1, K2:V2, K3:V3,K4:V4,K5:V5}

3) Finally, we select Keys from table

select id, arrMap['K1'] K1, arrMap['K2'] K2, arrMap['K3'] K3, arrMap['K4'] K4, arrMap['K5'] K5, from (select id, str_to_map(concat_ws(',', (collect_list(kv)))) arrMap from (select id, n.pos, concat_ws(':', n.attribute, value[n.pos]) kv from  INPUT_TABLE lateral view posexplode(attributes) n as pos, attribute )T group by id) T1;

 

K1

K2

K3

K4

K5

A

V1

V2

V3

 

 

B

 

V2

 

 

 

C

V1

V2

V3

V4

V5

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