SQL lead function SQL Netezza

debugcn 投稿 Dev

Ahmed Mohammed Abdel Kader

I have a table which has the below sample for only one line_id.

LINE_ID|COLLECTION_DATE    |DSL_CARD_TYPE|
-------|-------------------|-------------|
1234567|2020-03-25 08:46:08|ADSL_PORT    |
1234567|2020-03-26 08:31:48|ADSL_PORT    |
1234567|2020-03-27 08:42:40|VDSL_PORT    |
1234567|2020-03-28 08:36:32|VDSL_PORT    |
1234567|2020-03-29 08:31:33|VDSL_PORT    |
1234567|2020-03-30 08:50:15|VDSL_PORT    |
1234567|2020-04-31 08:44:33|ADSL_PORT    |
1234567|2020-03-01 08:34:53|ADSL_PORT    |
1234567|2020-04-02 08:44:11|ADSL_PORT    |
1234567|2020-04-03 08:43:51|VDSL_PORT    |
1234567|2020-04-04 08:54:33|ADSL_PORT    |
1234567|2020-04-05 09:06:47|ADSL_PORT    |
1234567|2020-04-06 09:06:57|VDSL_PORT    |
1234567|2020-04-07 09:13:32|VDSL_PORT    |

What I need is to group DSL_CARD_TYPE and create a new column called Next_COLLECTION_DATE to get the next DSL_CARD_TYPE and return the first date in each Next_group but like below

LINE_ID|COLLECTION_DATE    |Next_COLLECTION_DATE  |DSL_CARD_TYPE|
-------|-------------------|----------------------|-------------|
1234567|2020-03-25 08:46:08|2020-03-27 08:42:40   |ADSL_PORT    |  
1234567|2020-03-27 08:42:40|2020-03-31 08:34:53   |VDSL_PORT    |
1234567|2020-03-31 08:34:53|2020-04-03 08:43:51   |ADSL_PORT    |
1234567|2020-04-03 08:43:51|2020-04-04 08:54:33   |VDSL_PORT    |   
1234567|2020-04-04 08:54:33|2020-04-06 09:06:57   |ADSL_PORT    |  
1234567|2020-04-06 09:06:57|2020-04-07 09:13:32   |VDSL_PORT    |

I have the below code and it returns the last date in each group

select line_id, dsl_card_type, min(collection_date), max(collection_date)
from (select v.*,
             row_number() over (partition by line_id order by collection_date) as seqnum,
             row_number() over (partition by line_id, dsl_card_type order by collection_date) as seqnum_2
      from ANALYTICS.tmp.V_PORTS_LINE_CARD_DATA_ALL v
      where collection_date >= '2020-07-27 00:00:00'
     ) v
group by line_id, dsl_card_type, (seqnum - seqnum_2);```

Gordon Linoff

You can do this using lead() and lag():

select line_id, dsl_card_type, collection_date, 
       lead(collection_date) over (partition by line_id order by collection_date)
from (select v.*,
             lag(dsl_card_type) over (partition by line_id order by collection_date) as prev_dsl_card_type
      from ANALYTICS.tmp.V_PORTS_LINE_CARD_DATA_ALL v
      where collection_date >= '2020-07-27 00:00:00'
     ) v
where prev_dsl_card_type is null or prev_dsl_card_type <> dsl_card_type;

Voila! No aggregation is needed.

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