Why string functions matter in queries in SQL - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select the first 3 characters of the name column.

SQL

SELECT SUBSTR(name, 1, [1]) FROM employees;

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

A3

B5

C1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 as length returns empty string.

Using 1 returns only the first character.

The SUBSTR function extracts a substring starting at position 1 with length 3, giving the first 3 characters.

2fill in blank

medium

Complete the code to convert the email column to lowercase.

SQL

SELECT [1](email) FROM users;

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ALOWER

BLENGTH

CTRIM

DUPPER

Attempts:

3 left

💡 Hint

Common Mistakes

Using UPPER instead of LOWER.

Using LENGTH which returns number, not string.

The LOWER function converts all letters in the string to lowercase.

3fill in blank

hard

Fix the error in the code to find the position of '@' in the email column.

SQL

SELECT INSTR(email, [1]) FROM contacts;

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A'at'

B@

C'@'

Dat

Attempts:

3 left

💡 Hint

Common Mistakes

Not using quotes around '@'.

Using the word 'at' instead of '@'.

The INSTR function needs the character '@' as a string, so it must be in quotes.

4fill in blank

hard

Fill both blanks to trim spaces and convert the username column to uppercase.

SQL

SELECT [1]([2](username)) FROM users;

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AUPPER

BLOWER

CTRIM

DSUBSTR

Attempts:

3 left

💡 Hint

Common Mistakes

Reversing the order of functions.

Using LOWER instead of UPPER.

First TRIM removes spaces, then UPPER converts to uppercase.

5fill in blank

hard

Fill all three blanks to create a dictionary of usernames and their email domains (part after '@').

SQL

SELECT [1], SUBSTR(email, INSTR(email, [2]) + 1) AS domain FROM users WHERE email [3] '%@%';

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

Ausername

B'@'

CLIKE

Demail

Attempts:

3 left

💡 Hint

Common Mistakes

Using email instead of username.

Not quoting '@' in INSTR.

Using = instead of LIKE.

We select username, extract domain after '@', and filter emails containing '@' using LIKE.