Sequencing in Teradata | 易学教程

问题

I would like to create a SELECT query that results in a view that is 30 fields long and 1 record thick. 2 records if we're counting the title.

The specific part of the larger query in question is:

WHERE CAST(EVENT_TIMESTAMP AS DATE) - CONTRACT_EFFECTIVE_DATE = 1

This produces the results desired - records where the days between EVENT_TIMESTAMP and CONTRACT_EFFECTIVE_DATE is 1.

But I'd like this for 30 days. Something like:

WHERE CAST(EVENT_TIMESTAMP AS DATE) - CONTRACT_EFFECTIVE_DATE = 1:30

Is that possible? I could just cut n paste the query 30 times and change the number 1 to the corresponding value. But surely there is a better way?

The results would look something like:

1 day   2 day   3 day   4 day
10       11       8      14

回答1:

That's another PIVOT query, lots of cut&paste again.

Assuming you want to count the number of rows matching each day range:

SELECT 
   COUNT(CASE WHEN CAST(EVENT_TIMESTAMP AS DATE) - CONTRACT_EFFECTIVE_DATE = 1 THEN 1 END) AS "1 day",
   COUNT(CASE WHEN CAST(EVENT_TIMESTAMP AS DATE) - CONTRACT_EFFECTIVE_DATE = 2 THEN 1 END) AS "2 day",
   COUNT(CASE WHEN CAST(EVENT_TIMESTAMP AS DATE) - CONTRACT_EFFECTIVE_DATE = 3 THEN 1 END) AS "3 day",
   COUNT(CASE WHEN CAST(EVENT_TIMESTAMP AS DATE) - CONTRACT_EFFECTIVE_DATE = 4 THEN 1 END) AS "4 day",
...
FROM tab
WHERE CAST(EVENT_TIMESTAMP AS DATE) - CONTRACT_EFFECTIVE_DATE <= 30

You could also put the calculation in a Derived Table, but this just looks simpler:

SELECT 
   COUNT(CASE WHEN diff = 1 THEN 1 END) AS "1 day",
   COUNT(CASE WHEN diff = 2 THEN 1 END) AS "2 day",
   COUNT(CASE WHEN diff = 3 THEN 1 END) AS "3 day",
   COUNT(CASE WHEN diff = 4 THEN 1 END) AS "4 day"
FROM 
 (
   SELECT CAST(EVENT_TIMESTAMP AS DATE) - CONTRACT_EFFECTIVE_DATE AS diff
   FROM tab
   WHERE diff <= 30
 ) AS dt

回答2:

Are you looking for this?

WHERE CAST(EVENT_TIMESTAMP AS DATE) - CONTRACT_EFFECTIVE_DATE BETWEEN 1 AND 30

I think BETWEEN is what you want.

来源：https://stackoverflow.com/questions/23527359/sequencing-in-teradata

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Sequence

teradata