LOCATE and INSTR in MySQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the LOCATE function do in MySQL?

LOCATE finds the position of a substring inside a string and returns the position as a number. If the substring is not found, it returns 0.

intermediate

How is INSTR different from LOCATE in MySQL?

INSTR also finds the position of a substring inside a string but does not accept a starting position argument. LOCATE can start searching from a specific position, INSTR always searches from the beginning.

beginner

Write the syntax of LOCATE function.

LOCATE(substring, string, start_position) - start_position is optional and tells where to start searching.

beginner

What will LOCATE('cat', 'concatenate') return?

It returns 4 because 'cat' starts at the 4th character in 'concatenate'.

beginner

If INSTR('hello world', 'o') is used, what is the output?

It returns 5 because the first 'o' appears at the 5th position in 'hello world'.

What does LOCATE('a', 'banana') return?

A 0

B 1

C 3

D 2

The first 'a' in 'banana' is at position 2.

Which function allows specifying a start position for searching a substring?

A LOCATE

B SUBSTRING

C INSTR

D LENGTH

LOCATE lets you specify where to start searching; INSTR does not.

What does INSTR('apple', 'p') return?

A 3

B 2

C 1

D 0

The first 'p' in 'apple' is at position 2.

If the substring is not found, what do LOCATE and INSTR return?

A 0

B -1

C NULL

D 1

Both return 0 when the substring is not found.

Which of these is a valid LOCATE usage?

A LOCATE('text', 'x')

B LOCATE('x', 'text', '3')

C LOCATE('x', 'text', 3)

D LOCATE('x')

LOCATE requires at least substring and string; start position is optional and must be a number.

Explain how LOCATE and INSTR functions work in MySQL and when you might use each.

Think about searching inside words and starting points.

Describe the difference in syntax and behavior between LOCATE and INSTR.

Focus on argument order and optional parameters.

Practice

1. What does the MySQL function LOCATE('cat', 'concatenate') return?

easy

A. 0

B. 4

C. 1

D. 7

Solution

1. Step 1: Understand LOCATE function behavior

   LOCATE returns the position of the first occurrence of the substring in the string, starting from the beginning by default.

2. Step 2: Find 'cat' in 'concatenate'

   The substring 'cat' starts at the 4th character in 'concatenate'.

3. Final Answer:

   4 -> Option B

4. Quick Check:

   LOCATE('cat', 'concatenate') = 4 [OK]

Hint: LOCATE returns first position of substring, counting from 1 [OK]

Common Mistakes:

• Counting from 0 instead of 1
• Confusing LOCATE with INSTR starting position
• Assuming substring not found returns NULL

2. Which of the following is the correct syntax to find the position of 'dog' in the string 'bulldog' starting search from position 5 using LOCATE?

easy

A. LOCATE('dog', 'bulldog') FROM 5

B. LOCATE('dog', 5, 'bulldog')

C. LOCATE('bulldog', 'dog', 5)

D. LOCATE('dog', 'bulldog', 5)

Solution

1. Step 1: Recall LOCATE syntax

   The correct syntax is LOCATE(substring, string, start_position).

2. Step 2: Match syntax with options

   LOCATE('dog', 'bulldog', 5) matches the correct order: substring 'dog', string 'bulldog', start position 5.

3. Final Answer:

   LOCATE('dog', 'bulldog', 5) -> Option D

4. Quick Check:

   LOCATE(substring, string, start) correct syntax [OK]

Hint: LOCATE syntax: substring, string, start position [OK]

Common Mistakes:

• Swapping string and substring order
• Using incorrect argument order
• Trying to use FROM keyword

3. What is the output of this query?

SELECT INSTR('hello world', 'o');

medium

A. 6

B. 8

C. 0

D. 5

Solution

1. Step 1: Understand INSTR function behavior

   INSTR returns the position of the first occurrence of the substring in the string, starting from the beginning.

2. Step 2: Find 'o' in 'hello world'

   The first 'o' appears at the 6th character in 'hello world'.

3. Final Answer:

   6 -> Option A

4. Quick Check:

   INSTR('hello world', 'o') = 6 [OK]

Hint: INSTR always starts searching from beginning [OK]

Common Mistakes:

• Choosing position of second 'o' instead of first
• Confusing INSTR with LOCATE with start position
• Assuming zero-based index

4. Identify the error in this query:

SELECT LOCATE('test', 'testing', 0);

medium

A. Start position cannot be zero; must be >= 1

B. String and substring arguments are swapped

C. No error; query is valid

D. LOCATE does not accept three arguments

Solution

1. Step 1: Check LOCATE start position rules

   The start position argument can be less than 1; it is treated as 1 with no error.

2. Step 2: Analyze the query

   The query uses 0 as start position, which is valid; the search starts from position 1.

3. Final Answer:

   No error; query is valid -> Option C

4. Quick Check:

   LOCATE start position <1 clamped to 1 [OK]

Hint: LOCATE start_position <1 is allowed, search starts from 1 [OK]

Common Mistakes:

• Believing start position must be >=1 (it's clamped if less)
• Confusing argument order
• Assuming LOCATE uses zero-based indexing

5. Given the string 'abracadabra', which query returns the position of the second occurrence of 'a' using LOCATE?

hard

A. SELECT LOCATE('a', 'abracadabra', LOCATE('a', 'abracadabra') + 1);

B. SELECT INSTR('abracadabra', 'a', 2);

C. SELECT LOCATE('a', 'abracadabra', 5);

D. SELECT LOCATE('a', 'abracadabra', 1);

Solution

1. Step 1: Find first occurrence of 'a'

   LOCATE('a', 'abracadabra') returns 1, the position of the first 'a'.

2. Step 2: Use LOCATE with start position after first 'a'

   To find the second 'a', start searching from position 2 (1 + 1) using LOCATE('a', 'abracadabra', 2).

3. Step 3: Combine steps in one query

   Use nested LOCATE: LOCATE('a', 'abracadabra', LOCATE('a', 'abracadabra') + 1) to get second occurrence.

4. Final Answer:

   SELECT LOCATE('a', 'abracadabra', LOCATE('a', 'abracadabra') + 1); -> Option A

5. Quick Check:

   Nested LOCATE finds second occurrence [OK]

Hint: Use nested LOCATE with start = first position + 1 [OK]

Common Mistakes:

• Using INSTR with start position (not supported)
• Starting search at wrong position
• Not adding 1 to first occurrence position