21 real Isolation Levels questions from the SQL bank, as asked in Indian campus drives and tech interviews. Every question has a verified answer and an AI-tutor explanation on placd — free to start.
1. What is Read Uncommitted?
Junior
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
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
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
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
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
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"?
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
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
11. Which term means: "the strictest level, which makes concurrent transactions behave as if they ran one after another with no interleaving anomalies"?
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
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
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
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
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"?
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
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
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"?
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
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