SQL SUBSTRING Function
Quick summary: The SQL SUBSTRING() function extracts a portion of a string.
SQL SUBSTRING Syntax
SUBSTRING(string [FROM start] [FOR length])SQL
SQL SUBSTRING Basic examples
SELECT SUBSTRING('abcdef', 2, 3);SQL
Output:
bcdExtracts a substring starting at position 2.
SQL SUBSTRING Real-world usage
SELECT SUBSTRING(email, 1, 5) FROM users;SQL
Output:
Email prefixesExtracts partial values.
SQL SUBSTRING Edge cases
SELECT SUBSTRING('abc', 10, 2);SQL
Output:
Empty stringReturns empty string when start position exceeds length.
SQL SUBSTRING Common mistakes
Assuming zero-based indexes
SUBSTRING positions start at 1.
Incorrect
SUBSTRING('abc', 0, 1)Correct
SUBSTRING('abc', 1, 1)Use 1-based indexing.
SQL SUBSTRING Frequently Asked Questions
What does SUBSTRING() do in SQL?
Extracts a portion of a string.
Use case of SUBSTRING()?
Parsing text.
Syntax?
SUBSTRING(str, start, length).
Index start?
Usually starts at 1.
Common mistake?
Wrong index base.
Alternative?
SUBSTR.
Return type?
String.
Performance?
Fast.
Handles out of range?
Returns partial or empty.
Used in SELECT?
Yes.
Supports negative index?
Depends on DB.
Best practice?
Validate indexes.