mysql字符怎么连接_mysql中字符串连接用什么函数
MySql连接字符串
The value is ignored if Unix socket is used.
Use this to connect to a server in a replicated server configuration without concern on which server to use.
Use SSL if the server supports it, but allow connection in all cases
Always use SSL. Deny connection if server does not support SSL.
Returns a MySqlDateTime object for invalid values and a System.DateTime object for valid values
Returns System.DateTime.MinValue valued System.DateTime object for invalid values and a System.DateTime object for valid values.
The use of auto enlist transactionscope (default behaviour) could cause trouble in medium trust environments.
Default behaviour is that parameters for stored routines (stored procedures) are checked against the server
Some permissions and value casting related errors reported fixed when using this connection option.
The default behaviour is to read tables mysql.proc/INFORMATION_SCHEMA.ROUTINES and try to map provided command parameter values to the called procedures parameters and type cast values accordingly.
This can be troublesome if permissions to the (aforementioned) sproc info tables are insufficient.
The driver will not automatically map the parameters so you must manually set parameter types and you must also make sure to add the parameters to the command object in the exact order as appeared in the procedure definition.
This is the default behaviour.
Default values are 0 and 100.
Makes an additional round trip to the server when obtaining a connection from the pool and connection state will be reset.
This is useful in load balancing scenarios when available servers change you don't want 100 constant connections in the pool pointing to only one server.
Specified in seconds, the amount of time after connection object creation the connection will be destroyed. Destruction will only happen when connections are returned to pool.
A connection might be long lived in the pool, however the connections server settings are updated (SHOW VARIABLES command) each time returned to the pool. This makes the client use of the connection object up to date with the correct server settings. However this causes a round trip and to optimize pooling performance this behaviour can be turned off.
The Windows Native Authentication Plugin must be installed for this to work.
Number of seconds between each keep-alive package send.
This enables Visual Studio wizards that bracket symbols with [] to work with Connector/Net. This option incurs a performance hit, so should only be used if necessary.
Use this one to specify the length in seconds to wait for a server connection before terminating the attempt and receive an error.
Use this one to instruct the provider to ignore any command prepare statements and prevent corruption issues with server side prepared statements.
Use this one to specify which network protocol to use for the connection.
"socket" is the default value used if the key isn't specified. Value "tcp" is an equivalent for "socket".
Use "pipe" to use a named pipes connection, "unix" for a Unix socket connection and "memory" to use MySQL shared memory.
It's possible to explicit set the shared memory object name used for communication.
It's possible to explicit set the pipe name used for communication, if not set, 'mysql' is the default value.
It is the port value of -1 that tells the driver to use named pipes network protocol. This is available on Windows only. The value is ignored if Unix socket is used.
Use this one to specify which character set to use to encode queries sent to the server.
Note that resultsets still are returned in the character set of the data returned.
MySql 中如何连接一列字符串
如何在MySQL中连接两个字符串
mysql如何实现多行查询结果合并成一行,mysql如何实现多行查询结果合并成一行网站简介信息
利用函数：group_concat(),实现一个ID对应多个名称时,原本为多行数据,把名称合并成一行.
其完整语法：
GROUP_CONCAT(expr)
该函数返回带有来自一个组的连接的非NULL值的字符串结果.其完整的语法如下所示：
GROUP_CONCAT([DISTINCT] expr [,expr ...]
[ORDER BY {unsigned_integer | col_name | expr}
[ASC | DESC] [,col_name ...]]
[SEPARATOR str_val])
mysql SELECT student_name,
- GROUP_CONCAT(test_score)
- FROM student
- GROUP BY student_name;
Or:
- GROUP_CONCAT(DISTINCT test_score
- ORDER BY test_score DESC SEPARATOR ' ')
在MySQL中,你可以获取表达式组合的连接值.你可以使用DISTINCT删去重复值.假若你希望多结果值进行排序,则应该使用 ORDER BY子句.若要按相反顺序排列,将 DESC (递减) 关键词添加到你要用ORDER BY 子句进行排序的列名称中.默认顺序为升序；可使用ASC将其明确指定. SEPARATOR 后面跟随应该被插入结果的值中间的字符串值.默认为逗号 (',').通过指定SEPARATOR '' ,你可以删除所有分隔符.
使用group_concat_max_len系统变量,你可以设置允许的最大长度. 程序中进行这项操作的语法如下,其中 val 是一个无符号整数：
SET [SESSION | GLOBAL] group_concat_max_len = val;
mysql字符串拼接
结果：
说明：将多个字符串连接成一个字符串,但是可以一次性指定分隔符～（concat_ws就是concat with separator）
GROUP_CONCAT([DISTINCT] expr [,expr ...] [ORDER BY {unsigned_integer | col_name | expr} [ASC | DESC] [,col_name ...]] [SEPARATOR str_val])
说明：
DISTINCT：去除重复值
expr [,expr ...]：一个或多个字段（或表达式）
ORDER BY {unsigned_integer | col_name | expr} [ASC | DESC] [,col_name ...]：根据字段或表达式进行排序,可多个
SEPARATOR str_val：分隔符（默认为英文逗号）
group_concat()函数在处理大数据的时候,会发现内容被截取了
怎么在mysql里做字符串连接
在mysql里做字符串连接主要用到"CONCAT"函数,主要使用方法如下：
这样查询出来的结果,就把原来ts_test里面的save_path和save_name组装到thumb字段里面！
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