TABLESAMPLE for random sampling in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select a random 10% sample of rows from the table named employees.

PostgreSQL

SELECT * FROM employees TABLESAMPLE [1] (10);

Drag options to blanks, or click blank then click option'

ASYSTEM

BRANDOM

CBERNOULLI

DHASH

Attempts:

3 left

💡 Hint

Common Mistakes

Using RANDOM which is not a valid TABLESAMPLE method in PostgreSQL.

Using BERNOULLI which is valid but less efficient than SYSTEM.

The SYSTEM method is a common TABLESAMPLE method in PostgreSQL to get a random sample of rows.

2fill in blank

medium

Complete the code to select a 5% random sample of rows using the BERNOULLI method.

PostgreSQL

SELECT * FROM sales TABLESAMPLE [1] (5);

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AHASH

BRANDOM

CSYSTEM

DBERNOULLI

Attempts:

3 left

💡 Hint

Common Mistakes

Using SYSTEM which samples pages, not rows.

Using RANDOM which is not a valid method.

The BERNOULLI method samples rows individually with the given percentage.

3fill in blank

hard

Fix the error in the code to correctly sample 20% of rows from the products table.

PostgreSQL

SELECT * FROM products TABLESAMPLE [1] (20);

Drag options to blanks, or click blank then click option'

ARANDOM

BSYSTEM

CBERNOULLI

DHASH

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting parentheses around the percentage.

Using an invalid method name.

The sampling percentage must be inside parentheses. The correct syntax is TABLESAMPLE SYSTEM (20).

4fill in blank

hard

Fill both blanks to select a 15% random sample of rows from the orders table using the BERNOULLI method.

PostgreSQL

SELECT * FROM orders TABLESAMPLE [1] ([2]);

Drag options to blanks, or click blank then click option'

ABERNOULLI

B10

C15

DSYSTEM

Attempts:

3 left

💡 Hint

Common Mistakes

Using SYSTEM instead of BERNOULLI.

Using 10 instead of 15 for the percentage.

The BERNOULLI method samples rows with the given percentage, which is 15% here.

5fill in blank

hard

Fill all three blanks to select a 25% random sample of rows from the customers table using the SYSTEM method.

PostgreSQL

SELECT * FROM customers TABLESAMPLE [1] ([2]) REPEATABLE ([3]);

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ABERNOULLI

BSYSTEM

C25

D12345

Attempts:

3 left

💡 Hint

Common Mistakes

Using BERNOULLI instead of SYSTEM.

Omitting the REPEATABLE clause or seed value.

The SYSTEM method samples pages randomly. The percentage is 25, and REPEATABLE uses a seed value like 12345 for repeatable results.