SUBSTRING extraction in SQL - Step-by-Step Execution

Concept Flow - SUBSTRING extraction

Start with full string

↓

Specify start position and length

↓

Extract substring from start position

↓

Return extracted substring

↓

End

The SUBSTRING function takes a full string, a start position, and a length, then extracts and returns the part of the string starting at that position with the given length.

Execution Sample

SQL

SELECT SUBSTRING('Hello World', 7, 5) AS extracted;

Extracts 5 characters from 'Hello World' starting at position 7.

Execution Table

Step	Input String	Start Position	Length	Action	Result
1	'Hello World'	7	5	Identify substring starting at 7 for length 5	'World'
2	N/A	N/A	N/A	Return extracted substring	'World'
3	N/A	N/A	N/A	End of execution	Execution stops

💡 Extraction complete; substring 'World' returned from position 7 with length 5.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
Input String	'Hello World'	'Hello World'	N/A	N/A
Start Position	7	7	N/A	N/A
Length	5	5	N/A	N/A
Extracted Substring	N/A	'World'	'World'	'World'

Key Moments - 2 Insights

Why does the substring start at position 7 and not 6?

In SQL, string positions start at 1, so position 7 points to the 'W' in 'Hello World'. This is shown in execution_table row 1 where start position 7 extracts 'World'.

What happens if the length exceeds the remaining string length?

The substring function extracts up to the end of the string without error. For example, if length was 10 starting at 7, it would return 'World' anyway, as shown by the logic in execution_table row 1.

Visual Quiz - 3 Questions

Look at the execution table, what is the extracted substring at step 1?

A 'Hello'

B 'World'

C 'Hello World'

D 'orld'

💡 Hint

Check the 'Result' column in execution_table row 1.

At which step does the function return the extracted substring?

A Step 2

B Step 1

C Step 3

D Step 4

💡 Hint

Look for the action 'Return extracted substring' in execution_table.

If the start position was 1 and length 5, what would the extracted substring be?

A 'World'

B 'Hello World'

C 'Hello'

D 'ello '

💡 Hint

Refer to how start position affects extraction in variable_tracker and concept_flow.

Concept Snapshot

SUBSTRING(string, start, length)
Extracts part of string starting at 'start' position (1-based)
Returns substring of given 'length'
If length exceeds string end, returns up to string end
Used to get parts of text data in SQL queries

Full Transcript

The SUBSTRING function in SQL extracts a part of a string starting from a specified position and for a specified length. Positions start at 1, meaning the first character is position 1. For example, SUBSTRING('Hello World', 7, 5) extracts 'World' because it starts at the 7th character and takes 5 characters. If the length is longer than the remaining string, it extracts until the end without error. The function returns the extracted substring as the result.