LPAD

Description

The LPAD function (Left Padding) pads a string on the left side with specified characters until it reaches the specified length. If the target length is less than the original string length, the string is truncated.

Syntax

LPAD(<str>, <len>, <pad>)

Parameters

Parameter	Description
<str>	The source string to be padded. Type: VARCHAR
<len>	Target string character length (not byte length). Type: INT
<pad>	The string used for padding. Type: VARCHAR

Return Value

Returns VARCHAR type, representing the padded or truncated string.

Padding rules:

• If len > original string length: Repeatedly pad on the left with pad string until total length reaches len
• If len = original string length: Return original string
• If len < original string length: Truncate string, return only first len characters
• Calculated by character length, supports UTF-8 multi-byte characters

Special cases:

• If any parameter is NULL, returns NULL
• If pad is empty string and len > str length, returns empty string
• If len is 0, returns empty string
• If len is negative, returns NULL

Examples

1. Basic left padding

SELECT LPAD('hi', 5, 'xy'), LPAD('hello', 8, '*');

+---------------------+-----------------------+
| LPAD('hi', 5, 'xy') | LPAD('hello', 8, '*') |
+---------------------+-----------------------+
| xyxhi               | ***hello              |
+---------------------+-----------------------+

2. String truncation

SELECT LPAD('hi', 1, 'xy'), LPAD('hello world', 5, 'x');

+---------------------+------------------------------+
| LPAD('hi', 1, 'xy') | LPAD('hello world', 5, 'x')  |
+---------------------+------------------------------+
| h                   | hello                        |
+---------------------+------------------------------+

3. NULL value handling

SELECT LPAD(NULL, 5, 'x'), LPAD('hi', NULL, 'x'), LPAD('hi', 5, NULL);

+---------------------+------------------------+----------------------+
| LPAD(NULL, 5, 'x')  | LPAD('hi', NULL, 'x')  | LPAD('hi', 5, NULL)  |
+---------------------+------------------------+----------------------+
| NULL                | NULL                   | NULL                 |
+---------------------+------------------------+----------------------+