Repeatable-read transaction

Asked Jan 05 '19 at 21:00

Active Jan 05 '19 at 21:21

Viewed 85 times

Table R (A) containing the records [(3), (4), (5)] and transactions T1 = UPDATE R SET A = A * 2; INSERT INTO A VALUES (6); and T2 = 'SELECT AVG (A) FROM R; SELECT AVG (A) FROM R' Knowing that transaction T2 is executed using repeatable-read which are the posible values returned by the second select?

I think that possible values are: 4 and 7.5? Am I right? Please let me know if I correctly understand repeatable-read.

edited Jan 05 '19 at 21:21

GMB

216,147
25
84
135

asked Jan 05 '19 at 21:00

Robert1428

If by *repeatable-read* you mean once before the update and once after then 4 and 7.5 is correct. – forpas Jan 05 '19 at 21:09
Why integer? @forpas – Robert1428 Jan 05 '19 at 21:19
What is the data type of the column A? – forpas Jan 05 '19 at 21:21
It's not specifed in the question – Robert1428 Jan 05 '19 at 21:23
No it's 7.5. Now I saw that you tagged Oracle. The data type is number something. So the result is a real number. – forpas Jan 05 '19 at 21:35
What's the timing of the individual statements, and when are the UPDATE statements committed? – Bob Jarvis - Слава Україні Jan 05 '19 at 23:16
Do you really mean `values returned by the second select?` Or maybe do you rather mean `values returned by the second TRANSACTION`? In the first case - yes - either 4 or 7.5. In the second case - two selects return a pair of values, either 4+4 or 7.5+7.5 (other combinations are not possible like 4+7.5 or 7.5+4) – krokodilko Jan 06 '19 at 00:32

Repeatable-read transaction

0 Answers0