SQL to find next greater records for each element - sqlite

Question

I've got a table defined like this:
CREATE TABLE event (t REAL, event TEXT, value);
For each record in the table which have event='type' and value='G' there will be two corresponding records with event='Z' - one with value=1 and one with value=0. Here is an example:
t | event | value
1624838448.123 | type | G
1624838448.123 | Z | 1
1624839543.215 | Z | 0
Note that there could be other event='Z' records that don't have corresponding type='G' records. I'm trying to write a query to find all the event='G' records that do have a corresponding type='G' record to use as the bounds for an additional query (or join?).
Note: The t value for the "type" event and the Z event where value=1 will always be the same.
So for instance if the table looked like this:
t | event | value
1624838448.123 | type | G
1624838448.123 | Z | 1
1624839543.215 | Z | 0
1624839555.555 | type | H
1624838555.555 | Z | 1
1624839602.487 | Z | 0
1624839999.385 | type | G
1624839999.385 | Z | 1
1624840141.006 | Z | 0
Then I want the results of the query to return this:
t1 | t2
1624838448.123 | 1624839543.215
1624839999.385 | 1624840141.006

Answer 1

From your comment:
There are always three records (ignoring any other events in between)
in chronological order: the "type" event, the first "Z" record with
the same timestamp, and the second "Z" record with a later timestamp
So, there is no need to return t1 separately since it is equal to t in the row where event = 'type' and value = 'G'.
For t2 you can use conditional aggregation with MIN() window function:
SELECT t1, t2
FROM (
SELECT t AS t1, event, value
MIN(CASE WHEN event = 'Z' AND value = '0' THEN t END) OVER (ORDER BY t ROWS BETWEEN 1 FOLLOWING AND UNBOUNDED FOLLOWING) t2
FROM Event
)
WHERE event = 'type' AND value = 'G'
See the demo.

Answer 2

I found a solution using the RANK() function. With this I get an intermediate table which has the same rank for both the "type" and first "Z" record, since they have the same timestamp, and a rank two greater for the second "Z" record. I use WITH so I can self join repeatedly without having to specify the same query over and over. I first join the "type" and first "Z" row by requiring that the type of two second record be greater than that of the first (so I only get the type:Z combination and not type:type, Z:type, or Z:Z). Then I self join again to get the rank-2 row which picks up the second Z record. Overall, the query looks like this:
WITH Seq(t,event,A,I)
AS
(
SELECT t, event, value,
RANK() OVER (ORDER BY t) I
FROM Event e1
WHERE (e1.event='type' OR e1.event='Z')
)
SELECT s2.t,s3.t
FROM Seq s1
INNER JOIN Seq s2 ON s1.I = s2.I AND s1.event < s2.event
INNER JOIN Seq s3 ON s1.I = s3.I-2
WHERE s1.value='G';