array_join
array_join
description
Syntax
VARCHAR array_join(ARRAY<T> arr, VARCHAR sep[, VARCHAR null_replace])
根据分隔符(sep)和替换NULL的字符串(null_replace), 将数组中的所有元素组合成一个新的字符串。 若sep为NULL，则返回值为NULL。 若null_replace为NULL，则返回值也为NULL。 若sep为空字符串，则不应用任何分隔符。 若null_replace为空字符串或者不指定，则直接丢弃数组中的NULL元素。
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