The ANSI/ISO standard SQL 92 refers to three different read phenomena when Transaction 1 reads data that Transaction 2 might have changed.
In the following examples, two transactions take place. In the first, Query 1 is performed. Then, in the second transaction, Query 2 is performed and committed. Finally, in the first transaction, Query 1 is performed again.
The queries use the following data table:
| id | name | age |
|---|---|---|
| 1 | Joe | 20 |
| 2 | Jill | 25 |
Read more about this topic: Isolation (database Systems)
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