IS DISTINCT FROM for NULL-safe comparison in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select rows where column_a is distinct from column_b, including NULL-safe comparison.

PostgreSQL

SELECT * FROM table_name WHERE column_a [1] column_b;

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

AIS NOT NULL

B=

C!=

DIS DISTINCT FROM

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' operator which returns NULL when comparing with NULL values.

Using '!=' which does not handle NULLs properly.

The IS DISTINCT FROM operator compares two values and treats NULLs as distinct values, unlike the standard = operator.

2fill in blank

medium

Complete the code to select rows where column_a is NOT distinct from column_b, including NULL-safe comparison.

PostgreSQL

SELECT * FROM table_name WHERE column_a [1] column_b;

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

AIS NOT DISTINCT FROM

BIS DISTINCT FROM

C=

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' which returns NULL when comparing NULLs.

Using '!=' which does not handle NULLs properly.

The IS NOT DISTINCT FROM operator returns true when values are equal or both NULL, providing NULL-safe equality comparison.

3fill in blank

hard

Fix the error in the WHERE clause to correctly compare column_a and column_b with NULL-safe comparison.

PostgreSQL

SELECT * FROM table_name WHERE column_a [1] column_b;

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

A=

B!=

CIS DISTINCT FROM

DIS NOT NULL

Attempts:

3 left

💡 Hint

Common Mistakes

Leaving '=' which causes NULL comparison issues.

Using '!=' which does not handle NULLs correctly.

Using IS DISTINCT FROM ensures NULL-safe comparison, unlike '=' which returns NULL if either side is NULL.

4fill in blank

hard

Fill both blanks to select rows where column_x is distinct from column_y and column_z is NOT distinct from column_w.

PostgreSQL

SELECT * FROM table_name WHERE column_x [1] column_y AND column_z [2] column_w;

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

AIS DISTINCT FROM

B=

CIS NOT DISTINCT FROM

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' or '!=' which do not handle NULLs properly.

Mixing up IS DISTINCT FROM and IS NOT DISTINCT FROM.

The first blank uses IS DISTINCT FROM to find rows where column_x and column_y differ including NULLs. The second blank uses IS NOT DISTINCT FROM to find rows where column_z and column_w are equal or both NULL.

5fill in blank

hard

Fill all three blanks to select rows where column_a is distinct from column_b, column_c is NOT distinct from column_d, and column_e is distinct from NULL.

PostgreSQL

SELECT * FROM table_name WHERE column_a [1] column_b AND column_c [2] column_d AND column_e [3] NULL;

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

AIS DISTINCT FROM

BIS NOT DISTINCT FROM

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' to compare with NULL which returns NULL instead of true/false.

Confusing IS DISTINCT FROM and IS NOT DISTINCT FROM.

The first blank uses IS DISTINCT FROM to compare column_a and column_b safely. The second blank uses IS NOT DISTINCT FROM for column_c and column_d. The third blank uses IS DISTINCT FROM to compare column_e with NULL safely.