MySQL的幾個實用字符串函數 (轉) 收藏
最近老婆問我要一個在mysql裏做行列轉換的sql語句,想了半天沒想出來,還是去網上搜一下吧,然後就發現了這篇文章,非常實用,特轉過了一起分享:)
原文地址:http://blog.54master.com/index.php/316158/viewspace-20836
1.1 MySQL的concat函數可以連接一個或者多個字符串 , 如
mysql > select concat ( '10' );
+--------------+
| concat ( '10' ) |
+--------------+
| 10 |
+--------------+
1 row in set ( 0.00 sec )
mysql > select concat ( '11' , '22' , '33' );
+------------------------+
| concat ( '11' , '22' , '33' ) |
+------------------------+
| 112233 |
+------------------------+
1 row in set ( 0.00 sec )
而Oracle的concat函數只能連接兩個字符串
SQL > select concat ( '11' , '22' ) from dual ;
1.2 MySQL的concat函數在連接字符串的時候,只要其中一個是NULL , 那麼將返回NULL
mysql > select concat ( '11' , '22' , null );
+------------------------+
| concat ( '11' , '22' , null ) |
+------------------------+
| NULL |
+------------------------+
1 row in set ( 0.00 sec )
而Oracle的concat函數連接的時候,只要有一個字符串不是NULL , 就不會返回NULL
SQL > select concat ( '11' , NULL ) from dual ;
CONCAT
--
11
2、concat_ws () 函數 , 表示concat with separator , 即有分隔符的字符串連接
如連接後以逗號分隔
mysql > select concat_ws ( ',' , '11' , '22' , '33' );
+-------------------------------+
| concat_ws ( ',' , '11' , '22' , '33' ) |
+-------------------------------+
| 11 , 22 , 33 |
+-------------------------------+
1 row in set ( 0.00 sec )
和concat不同的是 , concat_ws函數在執行的時候 , 不會因爲NULL值而返回NULL
mysql > select concat_ws ( ',' , '11' , '22' , NULL );
+-------------------------------+
| concat_ws ( ',' , '11' , '22' , NULL ) |
+-------------------------------+
| 11 , 22 |
+-------------------------------+
1 row in set ( 0.00 sec )
3、group_concat () 可用來行轉列 , Oracle沒有這樣的函數
完整的語法如下
group_concat ([ DISTINCT ] 要連接的字段 [ Order BY ASC / DESC 排序字段 ] [ Separator '分隔符' ])
如下例子
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 )
3.1 以id分組,把name字段的值打印在一行,逗號分隔 ( 默認 )
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 )
3.2 以id分組,把name字段的值打印在一行,分號分隔
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 )
3.3 以id分組,把去冗餘的name字段的值打印在一行,逗號分隔
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 )
3.4 以id分組,把name字段的值打印在一行,逗號分隔 , 以name排倒序
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 )
4、repeat () 函數,用來複制字符串 , 如下 'ab' 表示要複製的字符串,2表示複製的份數
mysql > select repeat ( 'ab' , 2 );
+----------------+
| repeat ( 'ab' , 2 ) |
+----------------+
| abab |
+----------------+
1 row in set ( 0.00 sec )
又如
mysql > select repeat ( 'a' , 2 );
+---------------+
| repeat ( 'a' , 2 ) |
+---------------+
| aa |
+---------------+
1 row in set ( 0.00 sec )
原文地址:http://blog.54master.com/index.php/316158/viewspace-20836
MySQL的幾個實用字符串函數
1、concat () 函數1.1 MySQL的concat函數可以連接一個或者多個字符串 , 如
mysql > select concat ( '10' );
+--------------+
| concat ( '10' ) |
+--------------+
| 10 |
+--------------+
1 row in set ( 0.00 sec )
mysql > select concat ( '11' , '22' , '33' );
+------------------------+
| concat ( '11' , '22' , '33' ) |
+------------------------+
| 112233 |
+------------------------+
1 row in set ( 0.00 sec )
而Oracle的concat函數只能連接兩個字符串
SQL > select concat ( '11' , '22' ) from dual ;
1.2 MySQL的concat函數在連接字符串的時候,只要其中一個是NULL , 那麼將返回NULL
mysql > select concat ( '11' , '22' , null );
+------------------------+
| concat ( '11' , '22' , null ) |
+------------------------+
| NULL |
+------------------------+
1 row in set ( 0.00 sec )
而Oracle的concat函數連接的時候,只要有一個字符串不是NULL , 就不會返回NULL
SQL > select concat ( '11' , NULL ) from dual ;
CONCAT
--
11
2、concat_ws () 函數 , 表示concat with separator , 即有分隔符的字符串連接
如連接後以逗號分隔
mysql > select concat_ws ( ',' , '11' , '22' , '33' );
+-------------------------------+
| concat_ws ( ',' , '11' , '22' , '33' ) |
+-------------------------------+
| 11 , 22 , 33 |
+-------------------------------+
1 row in set ( 0.00 sec )
和concat不同的是 , concat_ws函數在執行的時候 , 不會因爲NULL值而返回NULL
mysql > select concat_ws ( ',' , '11' , '22' , NULL );
+-------------------------------+
| concat_ws ( ',' , '11' , '22' , NULL ) |
+-------------------------------+
| 11 , 22 |
+-------------------------------+
1 row in set ( 0.00 sec )
3、group_concat () 可用來行轉列 , Oracle沒有這樣的函數
完整的語法如下
group_concat ([ DISTINCT ] 要連接的字段 [ Order BY ASC / DESC 排序字段 ] [ Separator '分隔符' ])
如下例子
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 )
3.1 以id分組,把name字段的值打印在一行,逗號分隔 ( 默認 )
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 )
3.2 以id分組,把name字段的值打印在一行,分號分隔
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 )
3.3 以id分組,把去冗餘的name字段的值打印在一行,逗號分隔
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 )
3.4 以id分組,把name字段的值打印在一行,逗號分隔 , 以name排倒序
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 )
4、repeat () 函數,用來複制字符串 , 如下 'ab' 表示要複製的字符串,2表示複製的份數
mysql > select repeat ( 'ab' , 2 );
+----------------+
| repeat ( 'ab' , 2 ) |
+----------------+
| abab |
+----------------+
1 row in set ( 0.00 sec )
又如
mysql > select repeat ( 'a' , 2 );
+---------------+
| repeat ( 'a' , 2 ) |
+---------------+
| aa |
+---------------+
1 row in set ( 0.00 sec )