---
{
    "title": "ARRAY_JOIN",
    "language": "en"
}
---

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## array_join

array_join


### description

#### Syntax

`VARCHAR array_join(ARRAY<T> arr, VARCHAR sep[, VARCHAR null_replace])`

Combines all elements in the array to generate a new string according to the separator (sep) 
and the string to replace NULL (null_replace).
If sep is NULL, return NULL.
If null_replace is NULL, return NULL.
If sep is an empty string, no delimiter is applied.
If null_replace is an empty string or not specified, the NULL elements in the array are discarded directly.

### example

```
mysql> select k1, k2, array_join(k2, '_', 'null') from array_test order by k1;
+------+-----------------------------+------------------------------------+
| k1   | k2                          | array_join(`k2`, '_', 'null')      |
+------+-----------------------------+------------------------------------+
|  1   | [1, 2, 3, 4, 5]             | 1_2_3_4_5                          |
|  2   | [6, 7, 8]                   | 6_7_8                              |
|  3   | []                          |                                    |
|  4   | NULL                        | NULL                               |
|  5   | [1, 2, 3, 4, 5, 4, 3, 2, 1] | 1_2_3_4_5_4_3_2_1                  |
|  6   | [1, 2, 3, NULL]             | 1_2_3_null                         |
|  7   | [4, 5, 6, NULL, NULL]       | 4_5_6_null_null                    |
+------+-----------------------------+------------------------------------+

mysql> select k1, k2, array_join(k2, '_', 'null') from array_test01 order by k1;
+------+-----------------------------------+------------------------------------+
| k1   | k2                                | array_join(`k2`, '_', 'null')      |
+------+-----------------------------------+------------------------------------+
|  1   | ['a', 'b', 'c', 'd']              | a_b_c_d                            |
|  2   | ['e', 'f', 'g', 'h']              | e_f_g_h                            |
|  3   | [NULL, 'a', NULL, 'b', NULL, 'c'] | null_a_null_b_null_c               |
|  4   | ['d', 'e', NULL, ' ']             | d_e_null_                          |
|  5   | [' ', NULL, 'f', 'g']             |  _null_f_g                         |
+------+-----------------------------------+------------------------------------+

mysql> select k1, k2, array_join(k2, '_') from array_test order by k1;
+------+-----------------------------+----------------------------+
| k1   | k2                          | array_join(`k2`, '_')      |
+------+-----------------------------+----------------------------+
|  1   | [1, 2, 3, 4, 5]             | 1_2_3_4_5                  |
|  2   | [6, 7, 8]                   | 6_7_8                      |
|  3   | []                          |                            |
|  4   | NULL                        | NULL                       |
|  5   | [1, 2, 3, 4, 5, 4, 3, 2, 1] | 1_2_3_4_5_4_3_2_1          |
|  6   | [1, 2, 3, NULL]             | 1_2_3                      |
|  7   | [4, 5, 6, NULL, NULL]       | 4_5_6                      |
+------+-----------------------------+----------------------------+

mysql> select k1, k2, array_join(k2, '_') from array_test01 order by k1;
+------+-----------------------------------+----------------------------+
| k1   | k2                                | array_join(`k2`, '_')      |
+------+-----------------------------------+----------------------------+
|  1   | ['a', 'b', 'c', 'd']              | a_b_c_d                    |
|  2   | ['e', 'f', 'g', 'h']              | e_f_g_h                    |
|  3   | [NULL, 'a', NULL, 'b', NULL, 'c'] | a_b_c                      |
|  4   | ['d', 'e', NULL, ' ']             | d_e_                       |
|  5   | [' ', NULL, 'f', 'g']             |  _f_g                      |
+------+-----------------------------------+----------------------------+
```

### keywords

ARRAY, JOIN, ARRAY_JOIN