Read committed behavior in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start a transaction with read committed isolation level in PostgreSQL.

PostgreSQL

BEGIN TRANSACTION ISOLATION LEVEL [1];

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Aread committed

Bserializable

Crepeatable read

Dread uncommitted

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'read uncommitted' which is not supported in PostgreSQL.

Confusing 'repeatable read' with 'read committed'.

The read committed isolation level ensures that any data read is committed at the moment it is read. This is the default in PostgreSQL.

2fill in blank

medium

Complete the SQL query to select data inside a read committed transaction.

PostgreSQL

BEGIN TRANSACTION ISOLATION LEVEL read committed; SELECT * FROM [1]; COMMIT;

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Ausers

Btransactions

Corders

Dproducts

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing a table name that does not exist in the database.

Forgetting to commit the transaction.

The users table is selected here as an example to show data reading inside a read committed transaction.

3fill in blank

hard

Fix the error in the transaction isolation level syntax.

PostgreSQL

BEGIN TRANSACTION ISOLATION [1] read committed;

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AAT

BLEVEL

CWITH

DON

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'WITH' or 'ON' which are invalid here.

Omitting the keyword entirely.

The correct syntax in PostgreSQL is BEGIN TRANSACTION ISOLATION LEVEL read committed;. The keyword between ISOLATION and read committed is LEVEL.

4fill in blank

hard

Fill both blanks to create a query that reads only committed data and avoids dirty reads.

PostgreSQL

SET TRANSACTION ISOLATION LEVEL [1]; SELECT * FROM [2] WHERE status = 'active';

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ALEVEL

Bread committed

Cusers

Dorders

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the blanks or using wrong keywords.

Using a table name that does not exist.

The command SET TRANSACTION ISOLATION LEVEL read committed; sets the isolation level correctly. The users table is used here to select active users.

5fill in blank

hard

Fill all three blanks to write a transaction that sets read committed isolation, updates a table, and commits.

PostgreSQL

BEGIN TRANSACTION ISOLATION LEVEL [1]; UPDATE [2] SET status = 'completed' WHERE id = [3]; COMMIT;

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Aread committed

Btasks

C42

Dserializable

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'serializable' instead of 'read committed' for this example.

Forgetting to commit the transaction.

Using a non-numeric id value.

This transaction sets the isolation level to read committed, updates the tasks table setting the status to 'completed' for the task with id 42, and then commits the changes.