How create a unique ID based on conditions in SQL? - sql

Question

I would like to get a new ID, no matter the format (in the example below 11,12,13...)
Based on the following condition:
Every time the days column value is greater then 1 and not null then current row and all following ones will get the same ID until a new value will meet the condition.
Within the same email
Below you can see the expected 1 (in the format of XX)
I thought about using two conditions with the following order between them
Every time the days column value is greater then 1 then all following rows will get the same ID until a new value will meet the condition.
2.AND When lag (previous) is equal to 0/1/null.

Answer 1

Assuming you have an EmailDate column over which you're ordering (a DATETIME field, really), try something like this:
WITH
TableNameWithEmailDateIDs AS (
SELECT
*,
ROW_NUMBER() OVER (
ORDER BY
Email DESC,
EmailDate
) AS EmailDateID
FROM
TableName
),
IDs AS (
SELECT
*,
LEAD(EmailDateID, 1) OVER (
ORDER BY
Email,
EmailDate
) AS LeadEmailDateID
FROM
(
SELECT
*,
-- REMOVE +10 if you don't want 11 to be starting ID
ROW_NUMBER() OVER (
ORDER BY
Email DESC,
EmailDate
)+10 AS ID
FROM
TableNameWithEmailDateIDs
WHERE
Days > 1
OR Days IS NULL
) X
)
SELECT
COALESCE(TableName.EmailDate, IDs.EmailDate) AS EmailDate,
IDs.Email,
COALESCE(TableName.Days, IDs.Days) AS Days,
IDs.ID
FROM
IDs
LEFT JOIN TableNameWithEmailDateIDs TableName
ON IDs.Email = TableName.Email
AND TableName.EmailDateID BETWEEN
IDs.EmailDateID
AND IDs.LeadEmailDateID-1
ORDER BY
ID DESC,
TableName.EmailDate DESC
;
First, create a CTE that generates IDs for each distinct Email/Date combo (helpful for LEFT JOIN condition later). Then, create a CTE that generates IDs for rows that meet your condition (i.e. the important rows). Finally, LEFT JOIN your main table onto that CTE to fill in the "gaps", so to speak.
I suggest running each of the components of this query independently to fully understand what's going on.
Hope it helps!