SUBSTRING and LEFT/RIGHT in MySQL - Step-by-Step Execution

Concept Flow - SUBSTRING and LEFT/RIGHT

Start with input string

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Choose function: SUBSTRING / LEFT / RIGHT

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Determine start position and length

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Extract substring accordingly

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Return extracted substring

This flow shows how MySQL extracts parts of a string using SUBSTRING, LEFT, or RIGHT functions by specifying start positions and lengths.

Execution Sample

MySQL

SELECT SUBSTRING('Hello World', 7, 5) AS sub,
       LEFT('Hello World', 5) AS left_part,
       RIGHT('Hello World', 5) AS right_part;

Extracts 'World' using SUBSTRING, 'Hello' using LEFT, and 'World' using RIGHT from the string 'Hello World'.

Execution Table

Step	Function	Input String	Parameters	Extracted Substring	Explanation
1	SUBSTRING	'Hello World'	start=7, length=5	'World'	Start at 7th char, take 5 chars
2	LEFT	'Hello World'	length=5	'Hello'	Take first 5 chars from left
3	RIGHT	'Hello World'	length=5	'World'	Take last 5 chars from right
4	END				All functions executed, extraction complete

💡 All substring extractions done as per parameters, no more steps.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
Input String	'Hello World'	'Hello World'	'Hello World'	'Hello World'	'Hello World'
SUBSTRING Result	NULL	'World'	'World'	'World'	'World'
LEFT Result	NULL	NULL	'Hello'	'Hello'	'Hello'
RIGHT Result	NULL	NULL	NULL	'World'	'World'

Key Moments - 3 Insights

Why does SUBSTRING('Hello World', 7, 5) return 'World'?

Because the 7th character in 'Hello World' is 'W', and taking 5 characters from there gives 'World' as shown in execution_table row 1.

What happens if LEFT('Hello World', 5) is used?

It extracts the first 5 characters from the left, which is 'Hello', as shown in execution_table row 2.

How does RIGHT('Hello World', 5) differ from LEFT?

RIGHT takes characters from the end (right side) of the string, so it returns 'World' as in execution_table row 3.

Visual Quiz - 3 Questions

Look at the execution table, what substring does SUBSTRING('Hello World', 7, 5) extract?

A 'World'

B 'Hello'

C 'World!'

D 'Hello W'

💡 Hint

Check execution_table row 1 under Extracted Substring column.

At which step does LEFT('Hello World', 5) get executed and what is the result?

A Step 1, 'World'

B Step 2, 'Hello'

C Step 3, 'World'

D Step 2, 'World'

💡 Hint

Refer to execution_table row 2 for LEFT function details.

If we change RIGHT('Hello World', 3), what would be the extracted substring?

A 'orld'

B 'ld'

C 'rld'

D 'World'

💡 Hint

RIGHT extracts from the end; 3 characters means last 3 letters of 'Hello World'.

Concept Snapshot

SUBSTRING(str, start, length): Extracts substring from 'start' position for 'length' chars.
LEFT(str, length): Extracts first 'length' chars from left.
RIGHT(str, length): Extracts last 'length' chars from right.
Positions start at 1.
If length exceeds string, returns up to string end.
Useful for slicing strings in MySQL.

Full Transcript

This lesson shows how to extract parts of a string in MySQL using SUBSTRING, LEFT, and RIGHT functions. SUBSTRING takes a string, a start position, and a length to return a substring. LEFT returns the first N characters from the start of the string. RIGHT returns the last N characters from the end. Positions start counting at 1. For example, SUBSTRING('Hello World', 7, 5) returns 'World' because it starts at the 7th character and takes 5 characters. LEFT('Hello World', 5) returns 'Hello', the first 5 characters. RIGHT('Hello World', 5) returns 'World', the last 5 characters. These functions help you get parts of strings easily in SQL queries.