MySQL C API中的预处理语句
MySQL客户端/服务器协议提供了预处理语句。该功能采用了由mysql_stmt_init()初始化函数返回的MYSQL_STMT语句处理程序数据结构。对于多次执行的语句,预处理执行是一种有效的方式。首先对语句进行解析,为执行作好准备。接下来,在以后使用初始化函数返回的语句句柄执行一次或多次。
对于多次执行的语句,预处理执行比直接执行快,主要原因在于,仅对查询执行一次解析操作。在直接执行的情况下,每次执行语句时,均将进行查询。此外,由于每次执行预处理语句时仅需发送参数的数据,从而减少了网络通信量。
预处理语句的另一个优点是,它采用了二进制协议,从而使得客户端和服务器之间的数据传输更有效率。下述语句可用作预处理语句:CREATE TABLE、DELETE、DO、INSERT、REPLACE、SELECT、SET、UPDATE、以及大多数SHOW语句。
1 MYSQL_BIND bind[3]; 2 memset(bind, 0, sizeof(bind)); 3 bind[4].buffer_type = MYSQL_TYPE_MEDIUM_BLOB; //数据类型 4 bind[4].buffer = buf; //指向存储数据的内存空间的指针,一般是char型指针 5 bind[4].buffer_length = BUFFERSIZE_HTML; //内存空间的大小 6 bind[4].is_null = 0; //是否为NULL 7 bind[4].length = &length[4]; //实际数据的长度
我写的一个例子,是在Linux上运行的:
#include <mysql/my_global.h> #include <mysql.h> #include <string.h> #include <stdio.h> #include <time.h> #include <stdlib.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #define STRING_SIZE 50 //#define DROP_SAMPLE_TABLE "DROP TABLE IF EXISTS test_table" #define CREATE_SAMPLE_TABLE "CREATE TABLE test_table(urlMarkNumber SMALLINT,\ getTime DATETIME,\ url VARCHAR(100))" #define INSERT_SAMPLE "INSERT INTO test_table(urlMarkNumber,getTime,url) VALUES(?,?,?)" #define host "localhost" //my mysql server #define username "root" #define password "******" #define database "baike_baidu_com_html" int main(){ MYSQL *mysql; char *urlfile = "urllist.txt"; FILE *urlfp; //off_t size; char *pos; //printf("%d\n",sizeof(pos)); char *line = (char *)malloc(sizeof(char)*500); pos = (char *)malloc(sizeof(char) * 800); urlfp = fopen(urlfile,"r"); if(!(mysql = mysql_init(NULL))){ exit(-1); } if(mysql_options(mysql,MYSQL_SET_CHARSET_NAME,"utf8") != 0){ perror("mysql_options!"); exit(-1); } if(mysql_real_connect(mysql,host,username,password,database,0,NULL,0) == NULL){ int ret = mysql_errno(mysql); mysql_close(mysql); exit(-1); } MYSQL_STMT *stmt; MYSQL_BIND bind[3]; my_ulonglong affected_rows; int param_count; short small_data; int int_data; char str_data[STRING_SIZE]; unsigned long str_length; MYSQL_TIME dt; my_bool is_null; /*if (mysql_query(mysql, DROP_SAMPLE_TABLE)) { fprintf(stderr, " DROP TABLE failed\n"); fprintf(stderr, " %s\n", mysql_error(mysql)); exit(0); }*/ if (mysql_query(mysql, CREATE_SAMPLE_TABLE)) { fprintf(stderr, " CREATE TABLE failed\n"); fprintf(stderr, " %s\n", mysql_error(mysql)); exit(0); } /* Prepare an INSERT query with 3 parameters */ /* (the TIMESTAMP column is not named; the server */ /* sets it to the current date and time) */ stmt = mysql_stmt_init(mysql); if (!stmt) { fprintf(stderr, " mysql_stmt_init(), out of memory\n"); exit(0); } if (mysql_stmt_prepare(stmt, INSERT_SAMPLE, strlen(INSERT_SAMPLE))) { fprintf(stderr, " mysql_stmt_prepare(), INSERT failed\n"); fprintf(stderr, " %s\n", mysql_stmt_error(stmt)); exit(0); } fprintf(stdout, " prepare, INSERT successful\n"); /* Get the parameter count from the statement */ param_count= mysql_stmt_param_count(stmt); fprintf(stdout, " total parameters in INSERT: %d\n", param_count); if (param_count != 3) /* validate parameter count */ { fprintf(stderr, " invalid parameter count returned by MySQL\n"); exit(0); } /* Bind the data for all 3 parameters */ memset(bind, 0, sizeof(bind)); /* INTEGER PARAM */ /* This is a number type, so there is no need to specify buffer_length */ bind[0].buffer_type= MYSQL_TYPE_SHORT; bind[0].buffer= (char *)&small_data; bind[0].is_null= &is_null; bind[0].length= 0; /* STRING PARAM */ bind[1].buffer_type= MYSQL_TYPE_DATETIME; bind[1].buffer= (char *)&dt; bind[1].is_null= 0; bind[1].length= 0; /* SMALLINT PARAM */ bind[2].buffer_type= MYSQL_TYPE_VAR_STRING; bind[2].buffer= (char *)&str_data; bind[2].is_null= 0; bind[2].length= &str_length; /* Bind the buffers */ if (mysql_stmt_bind_param(stmt, bind)) { fprintf(stderr, " mysql_stmt_bind_param() failed\n"); fprintf(stderr, " %s\n", mysql_stmt_error(stmt)); exit(0); } /* Specify the data values for the first row */ small_data= 10; /* integer */ strncpy(str_data, "MySQL", STRING_SIZE); /* string */ str_length= strlen(str_data); dt.year = 2013; dt.month = 4; dt.day = 10; dt.hour = 20; dt.minute = 20; dt.second = 0; /* INSERT SMALLINT data as NULL */ is_null= 1; /* Execute the INSERT statement - 1*/ if (mysql_stmt_execute(stmt)) { fprintf(stderr, " mysql_stmt_execute(), 1 failed\n"); fprintf(stderr, " %s\n", mysql_stmt_error(stmt)); exit(0); } /* Get the total number of affected rows */ affected_rows= mysql_stmt_affected_rows(stmt); fprintf(stdout, " total affected rows(insert 1): %lu\n", (unsigned long) affected_rows); if (affected_rows != 1) /* validate affected rows */ { fprintf(stderr, " invalid affected rows by MySQL\n"); exit(0); } /* Specify data values for second row, then re-execute the statement */ strncpy(str_data, "http://baike.baidu.com", STRING_SIZE); str_length= strlen(str_data); small_data= 1000; /* smallint */ is_null= 0; /* reset */ /* integer */ dt.year = 2013; dt.month = 4; dt.day = 10; dt.hour = 20; dt.minute = 20; dt.second = 0; /* Execute the INSERT statement - 2*/ if (mysql_stmt_execute(stmt)) { fprintf(stderr, " mysql_stmt_execute, 2 failed\n"); fprintf(stderr, " %s\n", mysql_stmt_error(stmt)); exit(0); } /* Get the total rows affected */ affected_rows= mysql_stmt_affected_rows(stmt); fprintf(stdout, " total affected rows(insert 2): %lu\n",(unsigned long) affected_rows); if (affected_rows != 1) /* validate affected rows */ { fprintf(stderr, " invalid affected rows by MySQL\n"); exit(0); } printf("line before close\n"); /* Close the statement */ if (mysql_stmt_close(stmt)) { fprintf(stderr, " failed while closing the statement\n"); fprintf(stderr, " %s\n", mysql_stmt_error(stmt)); exit(0); } printf("line behind close\n"); fclose(urlfp); printf("line behind fclose\n"); mysql_close(mysql); printf("line behind mysql_close\n"); //fclose(urlfp); exit(EXIT_SUCCESS); return 0;
}