目录
MySQL数据库数据类型
MySQL数据库定义了多种数据类型,下面是一些常见的MySQL数据类型及其对应的C/C++类型:
整数类型:
- TINYINT:有符号范围-128到127,无符号范围0到255。对应的C/C++类型为signed char或unsigned char。
- SMALLINT:有符号范围-32768到32767,无符号范围0到65535。对应的C/C++类型为short或unsigned short。
- INT:有符号范围-2147483648到2147483647,无符号范围0到4294967295。对应的C/C++类型为int或unsigned int。
- BIGINT:有符号范围-9223372036854775808到9223372036854775807,无符号范围0到18446744073709551615。对应的C/C++类型为long long或unsigned long long。
浮点数类型:
- FLOAT:单精度浮点数。对应的C/C++类型为float。
- DOUBLE:双精度浮点数。对应的C/C++类型为double。
字符串类型:
- CHAR:固定长度字符串,最多255个字符。对应的C/C++类型为char数组。
- VARCHAR:可变长度字符串,最多65535个字符。对应的C/C++类型为char数组或std::string。
- TEXT:可变长度文本,最多65535个字符。对应的C/C++类型为char数组或std::string。
日期和时间类型:
- DATE:日期,格式为YYYY-MM-DD。对应的C/C++类型为struct tm或std::string。
- TIME:时间,格式为HH:MM:SS。对应的C/C++类型为struct tm或std::string。
- DATETIME:日期和时间,格式为YYYY-MM-DD HH:MM:SS。对应的C/C++类型为struct tm或std::string。
其他类型:
- BOOLEAN:布尔类型,值为TRUE或FALSE。对应的C/C++类型为bool。
- BLOB:二进制大对象,最多65535字节。对应的C/C++类型为unsigned char数组。
MySQL数据库命令执行
执行命令的过程:
- 发送SQL命令
- 获取SQL执行结果
- 解析获取到的结果
发送SQL命令接口
int STDCALL mysql_real_query(MYSQL *mysql, const char *q, unsigned long length);
q是SQL指令;length是指令的长度;向MySQL服务器发送SQL指令
获取SQL执行结果接口
MYSQL_RES *STDCALL mysql_use_result(MYSQL *mysql);
释放结果接口
void STDCALL mysql_free_result(MYSQL_RES *result);
获取结果集列的数量
unsigned int STDCALL mysql_num_fields(MYSQL_RES *res);
获取结果集行的数量
my_ulonglong STDCALL mysql_num_rows(MYSQL_RES *res);
取结果中的行接口
MYSQL_ROW STDCALL mysql_fetch_row(MYSQL_RES *result);
获取每一行的长度接口
unsigned long *STDCALL mysql_fetch_lengths(MYSQL_RES *result);
获取结果集中每一列的定义接口
MYSQL_FIELD *STDCALL mysql_fetch_fields(MYSQL_RES *res);
创建用户
CREATE USER '用户名'@'范围' IDENTIFIED BY '密码';
范围包括:ip、localhost、%
ip即只能从指定地址登录;localhost 即只能从本机登录;% 即可以从任何地址登录
光创建用户,并没有什么作用,还需要授权操作表
GRANT privileges ON databasename.tablename TO '用户名'@'范围'
privileges可以是:
SELECT,INSERT,UPDATE,DELETE,CREATE,DROP,ALTER,EXECUTE,INDEX,REFERENCES
ALTER ROUTINE,CREATE ROUTINE,CREATE TEMPORARY,SHOW VIEW,LOCK TABLES
ALL
databasename是库的名称,可以填入*表示所有
tablename是表的名称,可以填入*表示所有
有授权自然有撤销权限
REVOKE 权限 ON databasename.tablename FROM '用户名'@'范围'
#include <iostream>
#include <mysql.h>
#pragma comment(lib,"libmysql.lib")
int main()
{
MYSQL* mysql = new MYSQL();
//MYSQL mysql;//占用的是栈上的内存
MYSQL* pDB = mysql_init(mysql);
if (pDB == NULL) {
std::cout << "mysql_init failed!" << std::endl;
return -1;
}
pDB = mysql_real_connect(pDB, "localhost", "root", "123456", "mysql", 3306, NULL, 0);
std::cout << pDB << std::endl;
if (pDB) {
std::string sql = "CREATE USER 'hello'@'localhost' IDENTIFIED BY '123456'";
int ret = mysql_real_query(pDB, sql.c_str(), (unsigned long)sql.size());
if (ret != 0) {
std::cout << "mysql error:" << mysql_error(pDB) << std::endl;
}
MYSQL_RES* result = mysql_use_result(mysql);
if (result != NULL) {
unsigned nFields = mysql_num_fields(result);
my_ulonglong nRows = mysql_num_rows(result);
MYSQL_FIELD* fields = mysql_fetch_fields(result);
for (unsigned i = 0; i < nRows; i++) {
MYSQL_ROW row = mysql_fetch_row(result);
if (row != NULL) {
for (unsigned j = 0; j < nFields; j++) {
std::cout << "type:" << fields[j].type << " " << fields[j].name << ":" << row[j] << std::endl;
}
}
std::cout << "===================================================" << std::endl;
}
mysql_free_result(result);
}
sql = "GRANT ALL ON *.* TO 'hello'@'localhost'";
ret = mysql_real_query(pDB, sql.c_str(), (unsigned long)sql.size());
if (ret != 0) {
std::cout << "mysql error:" << mysql_error(pDB) << std::endl;
return -1;
}
result = mysql_use_result(mysql);
if (result != NULL) {
unsigned nFields = mysql_num_fields(result);
my_ulonglong nRows = mysql_num_rows(result);
MYSQL_FIELD* fields = mysql_fetch_fields(result);
for (unsigned i = 0; i < nRows; i++) {
MYSQL_ROW row = mysql_fetch_row(result);
if (row != NULL) {
for (unsigned j = 0; j < nFields; j++) {
std::cout << "type:" << fields[j].type << " " << fields[j].name << ":" << row[j] << std::endl;
}
}
std::cout << "===================================================" << std::endl;
}
mysql_free_result(result);
}
mysql_close(pDB);
}
delete mysql;
}
创建删除库
MySQL如何创建数据仓库
CREATE DATABASE 数据仓库名;
数据库名称不要使用奇怪的或者特殊的符号,例如空格、路径符、引号
MySQL如何指派仓库权限给用户
GRANT 权限 ON databasename.tablename TO '用户名'@'范围'
删除库
DROP DATABASE 数据仓库名;
切换数据库
USE 数据仓库名;
用户、数据库、表等等,这些元素的创建,一般是不会有返回结果
仅仅有一个返回值,标明执行的结果是成功还是失败!
测试代码
#include <iostream>
#include <mysql.h>
#pragma comment(lib,"libmysql.lib")
void show_result(MYSQL_RES* result)
{
unsigned nFields = mysql_num_fields(result);
my_ulonglong nRows = mysql_num_rows(result);
MYSQL_FIELD* fields = mysql_fetch_fields(result);
for (unsigned i = 0; i < nRows; i++)
{
MYSQL_ROW row = mysql_fetch_row(result);
if (row != NULL) {
for (unsigned j = 0; j < nFields; j++) {
std::cout << "type:" << fields[j].type << " " << fields[j].name << ":" << row[j] << std::endl;
}
}
}
}
int main()
{
MYSQL* mysql = new MYSQL();
//MYSQL mysql;//占用的是栈上的内存
MYSQL* pDB = mysql_init(mysql);
if (pDB == NULL) {
std::cout << "mysql_init failed!" << std::endl;
return -1;
}
pDB = mysql_real_connect(pDB, "localhost", "root", "123456", "mysql", 3306, NULL, 0);
std::cout << pDB << std::endl;
if (pDB) {
std::string sql = "CREATE DATABASE hello";
int ret = mysql_real_query(pDB, sql.c_str(), (unsigned long)sql.size());
if (ret != 0) {
std::cout << "mysql error:" << mysql_error(pDB) << std::endl;
}
MYSQL_RES* result = mysql_use_result(mysql);
if (result != NULL) {
show_result(result);
std::cout << "===================================================" << std::endl;
mysql_free_result(result);
}
//授予权限
sql = "GRANT ALL ON hello.* TO 'hello'@'localhost';";
ret = mysql_real_query(pDB, sql.c_str(), (unsigned long)sql.size());
if (ret != 0) {
std::cout << "mysql error:" << mysql_error(pDB) << std::endl;
return -1;
}
result = mysql_use_result(mysql);
if (result != NULL) {
show_result(result);
std::cout << "===================================================" << std::endl;
mysql_free_result(result);
}
sql = "USE hello;";
ret = mysql_real_query(pDB, sql.c_str(), (unsigned long)sql.size());
if (ret != 0) {
std::cout << "mysql error:" << mysql_error(pDB) << std::endl;
return -1;
}
result = mysql_use_result(mysql);
if (result != NULL) {
show_result(result);
std::cout << "===================================================" << std::endl;
mysql_free_result(result);
}
sql = "DROP DATABASE hello;";
ret = mysql_real_query(pDB, sql.c_str(), (unsigned long)sql.size());
if (ret != 0) {
std::cout << "mysql error:" << mysql_error(pDB) << std::endl;
return -1;
}
result = mysql_use_result(mysql);
if (result != NULL) {
show_result(result);
std::cout << "===================================================" << std::endl;
mysql_free_result(result);
}
mysql_close(pDB);
}
delete mysql;
return 0;
}
创建删除表
CREATE TABLE IF NOT EXISTS `表名称` (
`列名称1` 数据类型 关键字列表 默认值
...
)ENGINE=InnoDB DEFAULT CHARSET=utf8;
关键字和含义如下:
- AUTO_INCREMENT 自动增加,只能用于整数类型列
- NOT NULL 列不能为空
- NULL 列可以为空
- PRIMARY KEY 主键 表中主键的值是唯一的,可以用于标记和查找数据
- UNSIGNED 无符号的数,只能修饰整数类型列
- DEFAULT 默认值 用于指定列的默认值
- UNIQUE 唯一 该列的要么为NULL要么就必须是唯一的,不可重复
- ZEROFILL 0值填充,如果没有指定该列的值,则会填入0
以下为删除MySQL数据表的通用语法:
DROP TABLE `表名称` ;
主键的数据类型,它不能是可变长度的类型,例如:TEXT、BLOB
表名需要使用``符号来包围,千万不能使用单引号
测试代码
#include <iostream>
#include <mysql.h>
#pragma comment(lib,"libmysql.lib")
void show_result(MYSQL_RES* result)
{
unsigned nFields = mysql_num_fields(result);
my_ulonglong nRows = mysql_num_rows(result);
MYSQL_FIELD* fields = mysql_fetch_fields(result);
for (unsigned i = 0; i < nRows; i++)
{
MYSQL_ROW row = mysql_fetch_row(result);
if (row != NULL) {
for (unsigned j = 0; j < nFields; j++) {
std::cout << "type:" << fields[j].type << " " << fields[j].name << ":" << row[j] << std::endl;
}
}
}
}
int main()
{
MYSQL* mysql = new MYSQL();
//MYSQL mysql;//占用的是栈上的内存
MYSQL* pDB = mysql_init(mysql);
if (pDB == NULL) {
std::cout << "mysql_init failed!" << std::endl;
return -1;
}
pDB = mysql_real_connect(pDB, "localhost", "root", "123456", "mysql", 3306, NULL, 0);
std::cout << pDB << std::endl;
if (pDB) {
std::string sql = "CREATE DATABASE hello";
int ret = mysql_real_query(pDB, sql.c_str(), (unsigned long)sql.size());
if (ret != 0) {
std::cout << "mysql error:" << mysql_error(pDB) << std::endl;
}
MYSQL_RES* result = mysql_use_result(mysql);
if (result != NULL) {
show_result(result);
std::cout << "===================================================" << std::endl;
mysql_free_result(result);
}
//授予权限
sql = "GRANT ALL ON hello.* TO 'hello'@'localhost';";
ret = mysql_real_query(pDB, sql.c_str(), (unsigned long)sql.size());
if (ret != 0) {
std::cout << "mysql error:" << mysql_error(pDB) << std::endl;
return -1;
}
result = mysql_use_result(mysql);
if (result != NULL) {
show_result(result);
std::cout << "===================================================" << std::endl;
mysql_free_result(result);
}
sql = "USE hello;";
ret = mysql_real_query(pDB, sql.c_str(), (unsigned long)sql.size());
if (ret != 0) {
std::cout << "mysql error:" << mysql_error(pDB) << std::endl;
return -1;
}
result = mysql_use_result(mysql);
if (result != NULL) {
show_result(result);
std::cout << "===================================================" << std::endl;
mysql_free_result(result);
}
sql = "CREATE TABLE IF NOT EXISTS `hello` (`编号` NVARCHAR(16) PRIMARY KEY)ENGINE=InnoDB DEFAULT CHARSET=utf8;";
ret = mysql_real_query(pDB, sql.c_str(), (unsigned long)sql.size());
if (ret != 0) {
std::cout << "mysql error:" << mysql_error(pDB) << std::endl;
return -1;
}
sql = "DROP TABLE `hello`;";
ret = mysql_real_query(pDB, sql.c_str(), (unsigned long)sql.size());
if (ret != 0) {
std::cout << "mysql error:" << mysql_error(pDB) << std::endl;
return -1;
}
sql = "DROP DATABASE hello;";
ret = mysql_real_query(pDB, sql.c_str(), (unsigned long)sql.size());
if (ret != 0) {
std::cout << "mysql error:" << mysql_error(pDB) << std::endl;
return -1;
}
mysql_close(pDB);
}
delete mysql;
return 0;
}