C/C++语言中调用 sqlite 的函数操纵数据库(3)

5. 删除：delete

下面我们看看怎么在C语言中删除数据库中的特定的数据。

好的，我们现编辑一段c代码，取名为 delete.c

// name： delete.c
// This prog is used to test C/C++ API for sqlite3 .It is very simple,ha !
// Author : zieckey All rights reserved.
// date : 2006/11/18

#include <stdio.h>
#include <stdlib.h>
#include "sqlite3.h"
#define _DEBUG_

int main( void )
{
sqlite3 *db=NULL;
char *zErrMsg = 0;

int rc;

rc = sqlite3_open("zieckey.db", &db); //打开指定的数据库文件,如果不存在将创建一个同名的数据库文件
if( rc )
{
fprintf(stderr, "Can't open database: %sn", sqlite3_errmsg(db));
sqlite3_close(db);
exit(1);
}
else printf("You have opened a sqlite3 database named zieckey.db successfully!nCongratulations! Have fun ! ^-^ n");

//创建一个表,如果该表存在，则不创建，并给出提示信息，存储在 zErrMsg 中
char *sql = " CREATE TABLE SensorData(
ID INTEGER PRIMARY KEY,
SensorID INTEGER,
SiteNum INTEGER,
Time VARCHAR(12),
SensorParameter REAL
);" ;
sqlite3_exec( db , sql , 0 , 0 , &zErrMsg );

#ifdef _DEBUG_
printf("zErrMsg = %s n", zErrMsg);
#endif

//插入数据
sql = "INSERT INTO "SensorData" VALUES(NULL , 1 , 1 , '200605011206', 18.9 );" ;
sqlite3_exec( db , sql , 0 , 0 , &zErrMsg );

sql = "INSERT INTO "SensorData" VALUES(NULL , 23 , 45 , '200605011306', 16.4 );" ;
sqlite3_exec( db , sql , 0 , 0 , &zErrMsg );

sql = "INSERT INTO "SensorData" VALUES(NULL , 34 , 45 , '200605011306', 15.4 );" ;
sqlite3_exec( db , sql , 0 , 0 , &zErrMsg );

int nrow = 0, ncolumn = 0;
char **azResult; //二维数组存放结果

//查询数据
sql = "SELECT * FROM SensorData ";
sqlite3_get_table( db , sql , &azResult , &nrow , &ncolumn , &zErrMsg );
int i = 0 ;
printf( "row:%d column=%d n" , nrow , ncolumn );
printf( "nThe result of querying is : n" );
for( i=0 ; i<( nrow + 1 ) * ncolumn ; i++ )
printf( "azResult[%d] = %sn", i , azResult[i] );

//删除数据
sql = "DELETE FROM SensorData WHERE SensorID = 1 ;" ;
sqlite3_exec( db , sql , 0 , 0 , &zErrMsg );
#ifdef _DEBUG_
printf("zErrMsg = %s n", zErrMsg);
#endif
sql = "SELECT * FROM SensorData ";
sqlite3_get_table( db , sql , &azResult , &nrow , &ncolumn , &zErrMsg );
printf( "nnnnrow:%d column=%d " , nrow , ncolumn );
printf( "nAfter deleting , the result of querying is : n" );
for( i=0 ; i<( nrow + 1 ) * ncolumn ; i++ )
printf( "azResult[%d] = %sn", i , azResult[i] );

//释放掉 azResult 的内存空间
sqlite3_free_table( azResult );

#ifdef _DEBUG_
printf("zErrMsg = %s n", zErrMsg);
#endif

sqlite3_close(db); //关闭数据库
return 0;

}

下面我们编译运行看看，效果如何

[root@localhost temp]# export LD_LIBRARY_PATH=/usr/local/sqlite3/lib:$LD_LIBRARY_PATH
[root@localhost temp]# gcc delete.c -lsqlite3 -L/usr/local/sqlite3/lib -I/usr/local/sqlite3/include
delete.c:29:21: warning: multi-line string literals are deprecated
[root@localhost temp]# ./a.out
You have opened a sqlite3 database named zieckey.db successfully!
Congratulations! Have fun ! ^-^
zErrMsg = (null)
row:3 column=5

The result of querying is :
azResult[0] = ID
azResult[1] = SensorID
azResult[2] = SiteNum
azResult[3] = Time
azResult[4] = SensorParameter
azResult[5] = 1
azResult[6] = 1
azResult[7] = 1
azResult[8] = 200605011206
azResult[9] = 18.9
azResult[10] = 2
azResult[11] = 23
azResult[12] = 45
azResult[13] = 200605011306
azResult[14] = 16.4
azResult[15] = 3
azResult[16] = 34
azResult[17] = 45
azResult[18] = 200605011306
azResult[19] = 15.4
zErrMsg = (null)

 

row:2 column=5
After deleting , the result of querying is :
azResult[0] = ID
azResult[1] = SensorID
azResult[2] = SiteNum
azResult[3] = Time
azResult[4] = SensorParameter
azResult[5] = 2
azResult[6] = 23
azResult[7] = 45
azResult[8] = 200605011306
azResult[9] = 16.4
azResult[10] = 3
azResult[11] = 34
azResult[12] = 45
azResult[13] = 200605011306
azResult[14] = 15.4
zErrMsg = (null)

从程序输出结果就可以看出，在删除数据前，我们有三条记录，
删除数据后我们发现，数据库内记录少了。从而实现了我们的删除数据目的。

总结：
在这篇文章里，我们主要讲述了如何在C/C++语言中调用 sqlite 的函数接口来实现对数据库的管理，
包括创建数据库、创建表格、插入数据、查询数据、删除数据等。而这些操作似乎都很简单不是吗？