string

`LEFT / RIGHT`

LEFT returns the first n characters, RIGHT returns the last n characters. Available in Postgres and MySQL. SQLite has no LEFT/RIGHT — use SUBSTR(s, 1, n) for LEFT and SUBSTR(s, -n) for RIGHT.35+; a portable fallback is SUBSTRING(str, 1, n) or SUBSTRING(str, LENGTH(str)-n+1).

Syntax

LEFT(string, n)  |  RIGHT(string, n)

Parameters / Modifiers

Parameter	Purpose
n < 0	Postgres: return all except the last/first \|n\| characters
SUBSTRING(str, 1, n)	Portable equivalent of LEFT for older engines
RIGHT(str, n)	Mirror function returning the trailing n characters

Examples

SELECT LEFT('hello world', 5);

Returns 'hello'

SELECT RIGHT('hello world', 5);

Returns 'world'

SELECT LEFT(sku, 3), RIGHT(sku, 3) FROM products;

Extract 3-letter prefix and suffix from each SKU

SELECT RIGHT(phone, 4) FROM customers;

Last four digits of phone numbers

Dialect notes / Gotcha

SQLite has no LEFT/RIGHT functions; emulate with SUBSTR(str, 1, n) for LEFT and SUBSTR(str, -n) for RIGHT. Postgres and MySQL support both natively.

Related functions

SUBSTRING

Extracts a substring by 1-based start position and optional length. All three dialects support the comma-argument form; Postgres also accepts the SQL-standard FROM/FOR clauses and POSIX regex extraction.

LENGTH / CHAR_LENGTH

Returns the number of characters in a string (CHAR_LENGTH) or the number of bytes (LENGTH in MySQL). Postgres and SQLite LENGTH return character count for text, matching CHAR_LENGTH.

SPLIT_PART

Splits a string on a delimiter and returns the Nth part (1-based). Native to Postgres; MySQL emulates via SUBSTRING_INDEX and SQLite requires application-side splitting.

CONCAT

Joins two or more strings end-to-end and returns a single string. CONCAT is portable across MySQL, Postgres 9.1+, and SQLite 3.44+; the standard || operator works in Postgres and SQLite but not MySQL unless PIPES_AS_CONCAT is set.

REPLACE

Replaces every occurrence of from_str inside source with to_str. Case-sensitive in Postgres and SQLite; MySQL follows the column's collation.

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