REVERSE

Description

The REVERSE function is used to reverse the order of an input sequence. For string arguments, it returns a string with the character order reversed; for array arguments, it returns an array with the element order reversed. This function reverses by character and can correctly handle UTF-8 multi-byte characters.

Syntax

REVERSE(<seq>)

Parameters

Parameter	Description
<seq>	The string or array to reverse. Type: VARCHAR or ARRAY

Return Value

Returns the reversed sequence of the same type as the input:

• String input: Returns VARCHAR type, a string with reversed character order
• Array input: Returns ARRAY type, an array with reversed element order

Special cases:

• If parameter is NULL, returns NULL
• If string is empty, returns empty string
• If array is empty, returns empty array
• A single-character string remains the same after reversal

Examples

1. Basic string reversal

SELECT REVERSE('hello');

+------------------+
| REVERSE('hello') |
+------------------+
| olleh            |
+------------------+

2. Array element reversal

SELECT REVERSE(['hello', 'world']);

+-----------------------------+
| REVERSE(['hello', 'world']) |
+-----------------------------+
| ["world", "hello"]          |
+-----------------------------+

3. NULL value handling

SELECT REVERSE(NULL);

+---------------+
| REVERSE(NULL) |
+---------------+
| NULL          |
+---------------+

4. Empty string and empty array

SELECT REVERSE(''), REVERSE([]);

+-------------+-------------+
| REVERSE('') | REVERSE([]) |
+-------------+-------------+
|             | []          |
+-------------+-------------+

5. Single character and single element

SELECT REVERSE('A'), REVERSE(['single']);

+--------------+--------------------+
| REVERSE('A') | REVERSE(['single']) |
+--------------+--------------------+
| A            | ["single"]         |
+--------------+--------------------+

6. Numbers and special characters

SELECT REVERSE('12345'), REVERSE('!@#$%');

+------------------+------------------+
| REVERSE('12345') | REVERSE('!@#$%') |
+------------------+------------------+
| 54321            | %$#@!            |
+------------------+------------------+

7. UTF-8 multi-byte characters

SELECT REVERSE('ṭṛì ḍḍumai'), REVERSE('ḍḍumannàri');

+--------------------------------+----------------------------+
| REVERSE('ṭṛì ḍḍumai')          | REVERSE('ḍḍumannàri')      |
+--------------------------------+----------------------------+
| iamuḍḍ ìṛṭ                     | irànnamuḍḍ                 |
+--------------------------------+----------------------------+

8. Mixed character types

SELECT REVERSE('Hello123'), REVERSE('test@email.com');

+---------------------+--------------------------+
| REVERSE('Hello123') | REVERSE('test@email.com') |
+---------------------+--------------------------+
| 321olleH            | moc.liame@tset           |
+---------------------+--------------------------+

9. Multi-element array

SELECT REVERSE([1, 2, 3, 4, 5]), REVERSE(['a', 'b', 'c']);

+---------------------------+------------------------+
| REVERSE([1, 2, 3, 4, 5])  | REVERSE(['a', 'b', 'c']) |
+---------------------------+------------------------+
| [5, 4, 3, 2, 1]           | ["c", "b", "a"]        |
+---------------------------+------------------------+

10. Palindrome test

SELECT REVERSE('level'), REVERSE('12321');

+------------------+-------------------+
| REVERSE('level') | REVERSE('12321')  |
+------------------+-------------------+
| level            | 12321             |
+------------------+-------------------+