mysql done的作用
时间: 2023-11-21 21:55:34 浏览: 34
MySQL中的`mysql_query()`函数用于向MySQL服务器发送查询或命令。当查询成功时,它将返回一个资源标识符,您可以使用该标识符来获取结果集中的行。但是,当您只需要执行一个命令而不需要结果集时,使用`mysql_query()`函数会浪费服务器资源。这时,您可以使用`mysql_done()`函数来释放结果集并释放资源。`mysql_done()`函数的语法如下:
```c
int mysql_done(MYSQL_RES *result);
```
其中,`result`参数是由`mysql_store_result()`函数返回的结果集指针。`mysql_done()`函数返回0表示成功,返回非0值表示失败。
举个例子,如果您想要执行一个`INSERT`或`UPDATE`语句,您可以使用以下代码:
```c
if (mysql_query(&mysql, "UPDATE mytable SET name='John' WHERE id=1")) {
fprintf(stderr, "%s\n", mysql_error(&mysql));
exit(1);
}
mysql_done(mysql_store_result(&mysql));
```
这里,`mysql_query()`函数用于执行`UPDATE`语句,`mysql_store_result()`函数用于获取结果集(实际上没有结果集),然后`mysql_done()`函数用于释放结果集和资源。
相关问题
mysql 游标 REPEAT
引用:MySQL中的游标分为静态游标和动态游标两种类型。REPEAT游标是MySQL中的一个动态游标,它允许在同一次操作中多次遍历游标结果集,可以用来对结果集进行多次操作。 [^1]
下面是一个使用REPEAT游标的MySQL存储过程的例子,它将查询到的用户表中所有用户名转换成大写后插入到新表中:
```mysql
CREATE PROCEDURE cursor_demo() # 创建存储过程
BEGIN
DECLARE done INT DEFAULT FALSE; # 定义变量
DECLARE name CHAR(50);
DECLARE cur CURSOR FOR SELECT username FROM users; # 定义游标
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE; # 定义异常处理器
CREATE TABLE IF NOT EXISTS uppercase_users ( # 创建新表
username CHAR(50) NOT NULL,
PRIMARY KEY (username)
);
OPEN cur; # 打开游标
LOOP_FETCH: LOOP # 循环遍历结果集
FETCH cur INTO name;
IF done THEN
LEAVE LOOP_FETCH;
END IF;
INSERT INTO uppercase_users (username) VALUES (UPPER(name)); # 将用户名转换为大写并插入到新表中
END LOOP LOOP_FETCH;
CLOSE cur; # 关闭游标
END;
```
执行存储过程:
```mysql
CALL cursor_demo();
```
mysql syslog
MySQL syslog refers to the process of storing MySQL server logs in the system log file, which is also called the syslog. The syslog is a centralized logging system in Unix-based systems that collects and stores messages from various applications, services, and system components.
By default, MySQL server logs are stored in separate log files, but you can configure the server to send log messages to the syslog instead. This can be useful for centralizing log data and simplifying log management. To enable syslog logging in MySQL, you need to modify the MySQL configuration file (my.cnf) and specify the syslog facility and level for log messages. For example, you can add the following lines to the my.cnf file:
[mysqld]
log_syslog = ON
syslog_facility = daemon
syslog_ident = mysql
syslog_priority = info
Once this is done, MySQL will send log messages to the syslog with the specified facility, ident, and priority. You can then view the MySQL log messages in the system log file using standard syslog tools such as syslog-ng or rsyslog.