(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：