SQL使用记录

Daywei — Tue, 17 Mar 2015 07:43:00 GMT

摘要: 问题�Q�Update字段来自子查询或者来自其他表字段 Update 语句 Update 语句用于修改表中的数据�?语法�Q�UPDATE 表名�U?SET 列名�U?= 新�?WHERE 列名�U?= 某值SQL update select语句最常用的update语法是：(x��) UPDATE SET = 阅读全文

Daywei 2015-03-17 15:43 发表评论

C、C++写二�q�制数据到mysql的Blob字段

Daywei — Thu, 05 Jul 2012 08:06:00 GMT

-- 引子--

�׃��调试需要，需直接往数据库里写入二进制数据。本来这些数据是�׃��层��Y件来写的�Q�用的是C#。�ؓ(f��)�?ji��n)熟�?zh��n)?/span>C语言的数据库操作�Q�还是决定用C来写�q�段调试代码�?/span>

概况�Q?/span>

表名�Q?/span>Task

涉及(qi��ng)的字�D�及(qi��ng)属性：(x��)

NumDest�Q?/span>int(11) 用于存储目标数目

destIDs: blob 用于存储具体的目�?/span>ID

废话不多��_(d��)��入正题�?/span>

--二进制数据写�?-

二进制数据最为常见的��是囄��{�一些文件信息。虽然我�q�里不是�q�类型信息，但确实是二进制数据�?/span>

具体步骤�Q?/span>

1�?定义一�?/span>buffer�Q�如数组�Q�来存储sql语句

2�?把涉�?qi��ng)到二进制数据之前�?/span>sql语句��d��?/span>buffer中，可用sprintf�?/span>strcpy�{��?/span>

3�?�?/span>mysql_real_escape_string()函数��d��二进制数据到buffer中�?/span>

4�?加上剩余�?/span>sql语句�Q��Ş成完整的sql语句�?/span>

5�?利用mysql_real_query()函数来执�?/span>sql语句�?/span>

具体代码如下�Q?/span>

#include <stdio.h> #include <stdlib.h> #include <mysql/mysql.h> #include <stdint.h> #include <string.h> int main(int argc, char *argv[]) { MYSQL mysql; char sql[256], *end; int index, i; uint32_t *destIDs; if(argc != 2) { printf("enter error!\n"); exit(1); } index = atoi(argv[1]); printf("index: %d\n", index); destIDs = (uint32_t *)malloc(index * sizeof(uint32_t)); if(destIDs == NULL) printf("malloc error\n"); for(i=0; i<index; i++) destIDs[i] = i + 1; mysql_init(&mysql); if(!(mysql_real_connect(&mysql, "localhost", "root", "654321", "dbname", 0, NULL, 0))) { fprintf(stderr, "Couldn't connect to engine!\n%s\n", mysql_error(&mysql)); perror(""); exit(1); } sprintf(sql, "INSERT INTO Task(NumDest, DestIDs) VALUE (%u, ", index ); end = sql + strlen(sql); *end++ = '\''; end += mysql_real_escape_string(&mysql, end,(char *)destIDs, index*sizeof(uint32_t)); *end++ = '\''; *end++ = ')'; printf("end - sql: %d\n", (unsigned int)(end - sql)); if(mysql_real_query(&mysql, sql, (unsigned int)(end - sql))) { fprintf(stderr, "Query failed (%s)\n", mysql_error(&mysql)); exit(1); } mysql_close(&mysql); exit(0); #endif return 0; }

--��d��二进制文�?-

对于二进制文件的��d��Q�也�c�M��?/span>

具体步骤�Q?/span>

1,构造查询字�?/span>.

2,执行mysql _query查询. �Q�网上有说用mysql_real_query�Q�未实验�Q?/span>

3,�?/span>mysql_store_result存储�l�果.

4,�?/span>mysql_fetch_row取出一条记录处�?/span>.

具体代码如下�Q?/span>

#include <stdio.h> #include <stdlib.h> #include <stdint.h> #include <mysql/mysql.h> #include <string.h> int main(void) { int ret, i; char sql[256]; MYSQL mysql; MYSQL_RES *result; MYSQL_ROW row; uint32_t *destIDs, *temp; unsigned int destNum = 0; mysql_init(&mysql); if(!(mysql_real_connect(&mysql, "localhost", "root", "654321", "dbname", 0, NULL, 0))) { fprintf(stderr, "Couldn't connect to engine!\n%s\n", mysql_error(&mysql)); perror(""); exit(1); } sprintf(sql, "SELECT TaskID, NumDest, DestIDs FROM Task"); ret = mysql_query(&mysql, sql); if(ret != 0) { printf( "Failed to query task table: %s\n", mysql_error(&mysql)); return ret; } result = mysql_store_result(&mysql); if(result == NULL) { ret = mysql_errno(&mysql); printf( "Failed to store query result from task table:%s\n", mysql_error(&mysql)); return ret; } if((row = mysql_fetch_row(result)) != NULL) { sscanf(row[1], "%u", &destNum); destIDs = (uint32_t *)malloc(destNum * sizeof(uint32_t)); if(destIDs == NULL) { printf("malloc error!\n"); exit(1); } memcpy(destIDs, row[2], destNum * sizeof(uint32_t)); } mysql_free_result(result); printf("destNum: %d\n", destNum); temp = destIDs; for(i=0; i<destNum; i++) { printf("destIDs[%d]:%d\t", i+1, *temp++); } return ret; }

�׃��我这里可以根�?/span>NumDest获取��C��q�制的长度，所以不用再用函数去获取�?/span>

据网上信息，获取二进制信息长度应该这��P��(x��)“如果取出来的是二�q�制的数�?/span>,要确定它的长�?/span>,必须要用mysql_fetch_lengths函数取得光��?#8221;

int num_fields = mysql_num_fields(result); unsigned long *lengths = mysql_fetch_lengths(result); for(i=0; i<num_fields; i++) printf("Column: %u\t %lu bytes\n", i+1, lengths[i]); destIDs = (uint32_t *)malloc(lengths[2]); if(destIDs == NULL) { printf("malloc error!\n"); exit(1); } memcpy(destIDs, row[2], lengths[2]);

取二�q�制数据:

一��L(f��ng)��sql语句�Q�查询出来即可。只不过二进制数据是个数据块�Q�需要得到数据块的大��和数据指针�?/span>

bool CMySqlAccess::GetBinaryField(int nCol,char* &pDataOut,int& nDataLen)
{
if (m_ItemMySqlRow[nCol] != NULL)
{
unsigned long *FieldLength = mysql_fetch_lengths(m_pMySqlResult);
nDataLen = (int)FieldLength[nCol];
pDataOut = (char*)(m_ItemMySqlRow[nCol]);
return true;
}
else
{
return false;
}
}

像通常一��h��询后�Q�得到结果集�Q�然后得到第nCol列结果，�q�回二进制指针结果和二进刉��度。返回后必须立马处理或者存储一份。否则mysql��数据销毁，指针所指数据则无效�?ji��n)�?/span>

存二�q�制数据:

mysql语句接受的sql语句都是string�Q�以'\0'�l�尾的。如果冒然插入二�q�制数据到sql语句中，要么报错�Q�要么存储错误。此处可以通过mysql提供的函数将数据转换一下即可�?/span>

char* CMySqlAccess::ConvertBinaryToString(char* pBinaryData,int nLen)
{
static char s_BinaryData[10240];
mysql_real_escape_string(m_pMySqlConn,s_BinaryData,pBinaryData,nLen);
return s_BinaryData;
}
上面�q�个函数只能单线�E��用啊�Q�将一块二�q�制数据转换为mysql可识别的string数据。这样就直接可以通过mysql的sql语句insert�Q�update来对blob数据�q�行更新和插入了(ji��n)�Q�sql语句用法不变�?/span>

用例�Q?/span>

std::ostringstream strSQL;
strSQL<<"INSERT INTO "<<<",'"<ConvertBinaryToString(pData,nLen)<<"','')";
assert(m_pDBAccess);
m_pDBAccess->ExecuteSQL(strSQL.str());

playerdata是blob二进制类型，pData是指向一个结构体的指针，nLen是结构体的大��?/span>

上面��可以实��C��q�制的存储了(ji��n)�?/span>

�Ҏ(gu��)��二：(x��)

上面的方法，你会(x��)发现�Q�你每次都需要�{换数据，传指针，传大��等一�p�d��复杂操作�Q�是不是��序很�؜乱，�q�程很繁杂。mysql也�ؓ(f��)你提供了(ji��n)另外一�U�方法，那就是MYSQL_BIND。将数据操作�l�一化，�l�一�ȝ��(ch��)化。mysqlbind是一个结构体�Q�根据个��Z��同需求填充各个数据成员可以存储�Q意类型数据，当然包括blob�?/span>

bool CMySqlAccess::SetBinaryField(std::string& strCondition,void* pDataIn,int nDataLen)
{
if( ! mysql_stmt_prepare( m_pMySqlStmt, strCondition.c_str(), strCondition.length() ) )
{
memset(&m_MySqlBind,0,sizeof(MYSQL_BIND));
m_MySqlBind.buffer_type = MYSQL_TYPE_BLOB;
(*m_MySqlBind.length) = nDataLen;
memcpy(m_MySqlBind.buffer,pDataIn,nDataLen);
if(!mysql_stmt_bind_param(m_pMySqlStmt, (MYSQL_BIND *)&m_MySqlBind))
{
if(!mysql_stmt_execute(m_pMySqlStmt))
{
return true;
}
}
}
int nRes=GetDBErrorCode();
CLogOutStream errLog(crazy::ERROR_LEVEL,THIS_CLASS_NAME);
errLog<<"MySql Query Failed:\""<return false;
}

�q�个是对某一列blob数据�q�行存操作。pDataIn和nDataLen分别是一个struct�l�构体和�l�构体大��。填充完毕mysqlbind之后卛_��Ҏ(gu��)��据库二进制列�q�行存储�?ji��n)。可能你�?x��)问�Q�没有指定哪一列呢�Q�对。哪一列是在strCondition语句里面的，�q�是一个预处理语句。在预处理语句里面，有一个符�? ? 。问��P��问号的位�|�代表了(ji��n)mysqlbind数据对应的位�|��?/span>

INSERT INTO test_table(date_field, time_field, timestamp_field) VALUES(?,?,?�Q?/span>

上面�q�个语句�Q�有3个问�?三个问号分别对应test_table的三�?每个问号呢又对应一个mysqlbind数据�l�构。那么我们在mysql_stmt_bind_param函数调用�Ӟ��应该传入一个mysql_bind 数组。MYSQL_BIND m_MySqlBind[3].

填充整个数组数据�Q�即对应三个问号内容�?/span>

用例�Q?br />MYSQL_BIND bind[3];
MYSQL_STMT *stmt;

strmov(query, "INSERT INTO test_table(date_field, time_field, timestamp_field) VALUES(?,?,?");
//初始化stmt
stmt = mysql_stmt_init(mysql);
//预处理语�?br />mysql_stmt_prepare(mysql, query, strlen(query));
//初始化参�?br />bind[0].buffer_type= MYSQL_TYPE_DATE;
bind[0].buffer= (char *)&ts;
bind[0].is_null= 0;
bind[0].length= 0;
bind[1]= bind[2]= bind[0];
//�l�定参数123
mysql_stmt_bind_param(stmt, bind);
//执行预处理mysql语句
mysql_stmt_execute(stmt);

�q�没看懂��׃��人去看mysql文档�?ji��n)，其实里面讲得很清楚，只要扑֯�几个函数�Q�就可以把search出来�?br />
转自�Q?a >http://blog.chinaunix.net/uid-23842323-id-2656614.html
Reference�Q?a >http://topic.csdn.net/u/20090316/11/ac003f13-d1da-49a5-b12f-90e57cbe5ac9.html

Daywei 2012-07-05 16:06 发表评论

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SQL使用记录

C、C++写二�q�制数据到mysql的Blob字段