【MySQL】字符串鏈接

時間 2019-11-08

原文原文鏈接

CONCAT() 函數

能夠鏈接一或者多個字符串,不過其中若是有 Null 就直接返回 Nullmysql

mysql> select concat(11,22,33,44);
+---------------------+
| concat(11,22,33,44) |
+---------------------+
| 11223344            |
+---------------------+
1 row in set (0.00 sec)

mysql> select concat(11,22,null);
+--------------------+
| concat(11,22,null) |
+--------------------+
| NULL               |
+--------------------+
1 row in set (0.00 sec)

複製代碼

CONCAT_WS() 函數

以第一個佔位符爲分割,鏈接多個字符串,忽略 Nullsql

mysql> select concat_ws('',11,22,null);
+--------------------------+
| concat_ws('',11,22,null) |
+--------------------------+
| 1122                     |
+--------------------------+
1 row in set (0.00 sec)

mysql> select concat_ws('-',11,22,null,33);
+------------------------------+
| concat_ws('-',11,22,null,33) |
+------------------------------+
| 11-22-33                     |
+------------------------------+
1 row in set (0.00 sec)
複製代碼

group_concat()函數

完整的語法以下：
group_concat([DISTINCT] 要鏈接的字段 [Order BY ASC/DESC 排序字段] [Separator '分隔符'])函數

基本查詢ui

mysql> select * from aa;
+------+------+
|id | name   |
+------+------+
|1  | 10     |
|1  | 20     |
|1  | 20     |
|2  | 20     |
|3  | 200    |
|3  | 500    |
+------+------+
6 rows in set (0.00 sec)
複製代碼

以id分組，把name字段的值打印在一行，逗號分隔(默認)spa

mysql> select id,group_concat(name) from aa group by id;
+------+--------------------+
| id| group_concat(name) |
+------+--------------------+
|1 | 10,20,20|
|2 | 20 |
|3 | 200,500|
+------+--------------------+
3 rows in set (0.00 sec)
複製代碼

以id分組，把name字段的值打印在一行，分號分隔code

mysql> select id,group_concat(name separator ';') from aa group by id;
+------+----------------------------------+
| id| group_concat(name separator ';') |
+------+----------------------------------+
|1 | 10;20;20 |
|2 | 20|
|3 | 200;500   |
+------+----------------------------------+
3 rows in set (0.00 sec)
複製代碼

以id分組，把去冗餘的name字段的值打印在一行，blog

逗號分隔排序

mysql> select id,group_concat(distinct name) from aa group by id;
+------+-----------------------------+
| id| group_concat(distinct name) |
+------+-----------------------------+
|1 | 10,20|
|2 | 20   |
|3 | 200,500 |
+------+-----------------------------+
3 rows in set (0.00 sec)
複製代碼

以id分組，把name字段的值打印在一行，逗號分隔，以name排倒序字符串

mysql> select id,group_concat(name order by name desc) from aa group by id;
+------+---------------------------------------+
| id| group_concat(name order by name desc) |
+------+---------------------------------------+
|1 | 20,20,10   |
|2 | 20|
|3 | 500,200|
+------+---------------------------------------+
3 rows in set (0.00 sec)
複製代碼

repeat()函數

用來複制字符串,以下'ab'表示要複製的字符串，2表示複製的份數get

mysql> select repeat('ab',2);
+----------------+
| repeat('ab',2) |
+----------------+
| abab           |
+----------------+

1 row in set (0.00 sec)
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又如

mysql> select repeat('a',2);

+---------------+
| repeat('a',2) |
+---------------+
| aa            |
+---------------+
1 row in set (0.00 sec)
複製代碼

參照文章: Mysql中concat函數（鏈接字符串）

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