(二)不同数据库间的交叉数据查询插入等操作实现

在项目开发中，有时需要在两个数据库之间进行数据的操作，下面给出一例程来实现上述操作。

有这样两个数据库 MyDatabase.db 和 YourDatabase.db

MyDatabase.db中建立表test，如下:



YourDatabase.db中表test1和表test2，分别插入数据如下:


和

插入

(1)下面把上述YourDatabase.db两表中TestName插入到 MyDatabase.db 的test表中。

执行的SQL语句如下：

DELETE FROM TEST;
ATTACH DATABASE 'd:\YourDatabase.db' As 'ChildDatabase';
INSERT INTO test(ID,Test1Name,Test2Name) VALUES(1,(SELECT TestName from ChildDatabase.[test1] where id==1),(SELECT TestName from ChildDatabase.[test2] where id==1));
DETACH DATABASE ChildDatabase;

接下来是程序的实现过程：

#include "stdafx.h"

#include <stdlib.h>
#include <stdio.h>
#include <sqlite3.h>

static int callback(void *NotUsed, int argc, char **argv, char **azColName)
{
int i;
for(i=0; i<argc; i++)
{
printf("%s = %s\n", azColName[i], argv[i] ? argv[i] : "NULL");
}
printf("\n");
return 0;
}

int main(int argc, char* argv[])
{
sqlite3 *db1,*db2;
char *zErrMsg = 0;
int  rc1=0,rc2=0;
char *sql;

/* Open database */
rc1 = sqlite3_open("D:\\YourDatabase.db", &db1);
rc2 = sqlite3_open("D:\\MyDatabase.db", &db2);
if( rc1)
{
fprintf(stderr, "Can't open database: %s\n", sqlite3_errmsg(db1));
exit(0);
}
else
{
fprintf(stdout, "Opened database successfully\n");
}

if( rc2)
{
fprintf(stderr, "Can't open database: %s\n", sqlite3_errmsg(db2));
exit(0);
}
else
{
fprintf(stdout, "Opened database successfully\n");
}

sql ="DELETE FROM TEST;ATTACH DATABASE 'D:\\YourDatabase.db' As 'ChildDatabase';INSERT INTO test(ID,Test1Name,Test2Name) VALUES(1,(SELECT TestName from ChildDatabase.[test1] where id==1),(SELECT TestName from ChildDatabase.[test2] where id==1));DETACH DATABASE ChildDatabase;";

/* Execute SQL statement */
rc2 = sqlite3_exec(db2, sql, callback, 0, &zErrMsg);
if( rc2 != SQLITE_OK ){
fprintf(stderr, "SQL error: %s\n", zErrMsg);
sqlite3_free(zErrMsg);
}
else
{
fprintf(stdout, "Table created successfully\n");
}
sqlite3_close(db1);
sqlite3_close(db2);
system("pause");

return 0;
}

执行结果为：

查询

在表test的Test1Name查找表test1里的TestName名称相同的条目

SQL语句：

ATTACH DATABASE 'd:\YourDatabase.db' As 'ChildDatabase';
SELECT *FROM test WHERE Test1Name==(SELECT TestName FROM ChildDatabase.[test1]);
DETACH DATABASE ChildDatabase;

执行结果：