[Solved] Consider two transactions T1 and T2 running concurrently. T1 reads a row, then T2 updates and commits... If the isolation level is REPEATABLE READ, what will T1 see when it reads the same row again? | SQL

SQL - Transactions and Data Integrity

Consider two transactions T1 and T2 running concurrently. T1 reads a row, then T2 updates and commits that row. If the isolation level is REPEATABLE READ, what will T1 see when it reads the same row again?

AThe updated value committed by T2

BThe original value before T2's update

CAn error due to concurrent update

DA partially updated value

Step-by-Step Solution

Solution:

Step 1: Understand REPEATABLE READ and apply to scenario
REPEATABLE READ ensures a transaction sees the same data on repeated reads of the same row. T1's second read sees the original value despite T2's committed update.
Final Answer:
The original value before T2's update -> Option B
Quick Check:
REPEATABLE READ prevents non-repeatable reads = The original value before T2's update [OK]

Quick Trick: REPEATABLE READ keeps data stable during transaction [OK]

Common Mistakes:

Assuming T1 sees T2's committed update immediately
Confusing REPEATABLE READ with READ COMMITTED
Thinking it causes errors on concurrent updates

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If the isolation level is REPEATABLE READ, what will T1 see when it reads the same row again?

Step 1: Understand REPEATABLE READ and apply to scenario

Final Answer:

Quick Check:

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