21 Isolation Levels questions from the SQL bank, written for Indian campus drives and tech interviews. Every question has a verified answer and an AI-tutor explanation on placd.
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A.reading a row that another transaction has modified but not yet committed, which may later be rolled back
B.a level that lets a transaction see only committed data, so each statement reads the latest committed snapshot
C.an anomaly where re-running the same range query returns new rows inserted by another committed transaction, prevented only at the Serializable level
D.the weakest level, which allows a transaction to see rows written by other transactions that have not yet committed
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2. Which term means: "the weakest level, which allows a transaction to see rows written by other transactions that have not yet committed"?
Junior
A.Read Committed
B.Read Uncommitted
C.Non-repeatable read
D.Dirty read
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3. Which statement is correct?
Junior
A.Read Uncommitted — an anomaly where re-reading the same row inside one transaction returns different values because another transaction committed an update between the reads
B.Read Uncommitted — a level guaranteeing that rows already read keep the same values for the whole transaction, though new matching rows may still appear
C.Read Uncommitted — an anomaly where re-running the same range query returns new rows inserted by another committed transaction, prevented only at the Serializable level
D.Read Uncommitted — the weakest level, which allows a transaction to see rows written by other transactions that have not yet committed
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4. What is Read Committed?
Mid
A.a level guaranteeing that rows already read keep the same values for the whole transaction, though new matching rows may still appear
B.the strictest level, which makes concurrent transactions behave as if they ran one after another with no interleaving anomalies
C.an anomaly where re-reading the same row inside one transaction returns different values because another transaction committed an update between the reads
D.a level that lets a transaction see only committed data, so each statement reads the latest committed snapshot
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5. Which term means: "a level that lets a transaction see only committed data, so each statement reads the latest committed snapshot"?
Mid
A.Serializable
B.Read Committed
C.Read Uncommitted
D.Phantom read
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6. Which statement is correct?
Mid
A.Read Committed — a level guaranteeing that rows already read keep the same values for the whole transaction, though new matching rows may still appear
B.Read Committed — reading a row that another transaction has modified but not yet committed, which may later be rolled back
C.Read Committed — the weakest level, which allows a transaction to see rows written by other transactions that have not yet committed
D.Read Committed — a level that lets a transaction see only committed data, so each statement reads the latest committed snapshot
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7. What is Repeatable Read?
Mid
A.the weakest level, which allows a transaction to see rows written by other transactions that have not yet committed
B.a level that lets a transaction see only committed data, so each statement reads the latest committed snapshot
C.a level guaranteeing that rows already read keep the same values for the whole transaction, though new matching rows may still appear
D.an anomaly where re-running the same range query returns new rows inserted by another committed transaction, prevented only at the Serializable level
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8. Which term means: "a level guaranteeing that rows already read keep the same values for the whole transaction, though new matching rows may still appear"?
Mid
A.Repeatable Read
B.Non-repeatable read
C.Phantom read
D.Read Uncommitted
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9. Which statement is correct?
Mid
A.Repeatable Read — an anomaly where re-reading the same row inside one transaction returns different values because another transaction committed an update between the reads
B.Repeatable Read — a level guaranteeing that rows already read keep the same values for the whole transaction, though new matching rows may still appear
C.Repeatable Read — the strictest level, which makes concurrent transactions behave as if they ran one after another with no interleaving anomalies
D.Repeatable Read — reading a row that another transaction has modified but not yet committed, which may later be rolled back
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10. What is Serializable?
Mid
A.the strictest level, which makes concurrent transactions behave as if they ran one after another with no interleaving anomalies
B.a level that lets a transaction see only committed data, so each statement reads the latest committed snapshot
C.reading a row that another transaction has modified but not yet committed, which may later be rolled back
D.an anomaly where re-running the same range query returns new rows inserted by another committed transaction, prevented only at the Serializable level
Answer + AI explanation with Pro
11. Which term means: "the strictest level, which makes concurrent transactions behave as if they ran one after another with no interleaving anomalies"?
Mid
A.Read Committed
B.Non-repeatable read
C.Read Uncommitted
D.Serializable
Answer + AI explanation with Pro
12. Which statement is correct?
Mid
A.Serializable — the weakest level, which allows a transaction to see rows written by other transactions that have not yet committed
B.Serializable — an anomaly where re-reading the same row inside one transaction returns different values because another transaction committed an update between the reads
C.Serializable — reading a row that another transaction has modified but not yet committed, which may later be rolled back
D.Serializable — the strictest level, which makes concurrent transactions behave as if they ran one after another with no interleaving anomalies
Answer + AI explanation with Pro
13. What is Dirty read?
Mid
A.an anomaly where re-reading the same row inside one transaction returns different values because another transaction committed an update between the reads
B.the weakest level, which allows a transaction to see rows written by other transactions that have not yet committed
C.reading a row that another transaction has modified but not yet committed, which may later be rolled back
D.the strictest level, which makes concurrent transactions behave as if they ran one after another with no interleaving anomalies
Answer + AI explanation with Pro
14. Which term means: "reading a row that another transaction has modified but not yet committed, which may later be rolled back"?
Mid
A.Read Committed
B.Serializable
C.Dirty read
D.Phantom read
Answer + AI explanation with Pro
15. Which statement is correct?
Mid
A.Dirty read — the weakest level, which allows a transaction to see rows written by other transactions that have not yet committed
B.Dirty read — an anomaly where re-running the same range query returns new rows inserted by another committed transaction, prevented only at the Serializable level
C.Dirty read — a level that lets a transaction see only committed data, so each statement reads the latest committed snapshot
D.Dirty read — reading a row that another transaction has modified but not yet committed, which may later be rolled back
Answer + AI explanation with Pro
16. What is Non-repeatable read?
Mid
A.the weakest level, which allows a transaction to see rows written by other transactions that have not yet committed
B.reading a row that another transaction has modified but not yet committed, which may later be rolled back
C.the strictest level, which makes concurrent transactions behave as if they ran one after another with no interleaving anomalies
D.an anomaly where re-reading the same row inside one transaction returns different values because another transaction committed an update between the reads
Answer + AI explanation with Pro
17. Which term means: "an anomaly where re-reading the same row inside one transaction returns different values because another transaction committed an update between the reads"?
Mid
A.Serializable
B.Phantom read
C.Non-repeatable read
D.Read Committed
Answer + AI explanation with Pro
18. Which statement is correct?
Mid
A.Non-repeatable read — an anomaly where re-reading the same row inside one transaction returns different values because another transaction committed an update between the reads
B.Non-repeatable read — an anomaly where re-running the same range query returns new rows inserted by another committed transaction, prevented only at the Serializable level
C.Non-repeatable read — a level that lets a transaction see only committed data, so each statement reads the latest committed snapshot
D.Non-repeatable read — a level guaranteeing that rows already read keep the same values for the whole transaction, though new matching rows may still appear
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19. What is Phantom read?
Senior
A.an anomaly where re-running the same range query returns new rows inserted by another committed transaction, prevented only at the Serializable level
B.the strictest level, which makes concurrent transactions behave as if they ran one after another with no interleaving anomalies
C.reading a row that another transaction has modified but not yet committed, which may later be rolled back
D.an anomaly where re-reading the same row inside one transaction returns different values because another transaction committed an update between the reads
Answer + AI explanation with Pro
20. Which term means: "an anomaly where re-running the same range query returns new rows inserted by another committed transaction, prevented only at the Serializable level"?
Senior
A.Serializable
B.Phantom read
C.Repeatable Read
D.Read Committed
Answer + AI explanation with Pro
21. Which statement is correct?
Senior
A.Phantom read — a level that lets a transaction see only committed data, so each statement reads the latest committed snapshot
B.Phantom read — an anomaly where re-running the same range query returns new rows inserted by another committed transaction, prevented only at the Serializable level
C.Phantom read — the strictest level, which makes concurrent transactions behave as if they ran one after another with no interleaving anomalies
D.Phantom read — a level guaranteeing that rows already read keep the same values for the whole transaction, though new matching rows may still appear
Answer + AI explanation with Pro
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