COALESCE and NULLIF as CASE shortcuts in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to return the first non-null value between column1 and column2.

SQL

SELECT COALESCE(column1, [1]) AS result FROM table_name;

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

A'default'

Bcolumn3

CNULL

Dcolumn2

Attempts:

3 left

💡 Hint

Common Mistakes

Using a literal string instead of a column name.

Using NULL as the second argument which always returns NULL if column1 is NULL.

The COALESCE function returns the first non-null value from the list. Here, it checks column1 first, then column2.

2fill in blank

medium

Complete the code to return NULL if column1 equals column2, otherwise return column1.

SQL

SELECT NULLIF(column1, [1]) AS result FROM table_name;

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

Acolumn2

Bcolumn3

C'value'

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing column1 with a literal instead of column2.

Using COALESCE instead of NULLIF.

NULLIF returns NULL if the two arguments are equal. Here, it compares column1 and column2.

3fill in blank

hard

Fix the error in the code to return the first non-null value among column1, column2, and 'N/A'.

SQL

SELECT COALESCE([1], column2, 'N/A') AS result FROM table_name;

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

Acolumn3

B'N/A'

Ccolumn1

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Using a literal or NULL as the first argument instead of column1.

Putting 'N/A' before columns which prevents checking columns.

The first argument to COALESCE should be column1 to check it first for a non-null value.

4fill in blank

hard

Fill both blanks to return 'Unknown' if column1 equals column2, else return column1 or 'Unknown' if column1 is NULL.

SQL

SELECT COALESCE(NULLIF(column1, [1]), [2]) AS result FROM table_name;

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

Acolumn2

B'Unknown'

Ccolumn3

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Using NULL instead of 'Unknown' as fallback.

Comparing column1 with a wrong column.

NULLIF(column1, column2) returns NULL if equal, then COALESCE returns 'Unknown' if NULL, else column1.

5fill in blank

hard

Fill all three blanks to return the uppercase of column1 if UPPER(column1) is not equal to column2 and column1 is not NULL, else return 'DEFAULT'.

SQL

SELECT COALESCE(NULLIF([1], [2]), [3]) AS result FROM table_name;

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

AUPPER(column1)

Bcolumn2

C'DEFAULT'

Dcolumn1

Attempts:

3 left

💡 Hint

Common Mistakes

Using column1 instead of UPPER(column1).

Using NULL instead of 'DEFAULT' as fallback.

NULLIF compares UPPER(column1) and column2; if equal returns NULL, then COALESCE returns 'DEFAULT' if NULL.