数据库概念介绍

数据库安装

• 首先将本地的三个sqlite3安装包移动到共享文件夹然后在移动到自己创建的文件夹中如下：
  
• 然后对安装包进行解压如下：

  sudo dpkg -i  *.deb
  

• 检查是否安装成功

  sqlite
  

数据库命令

• 系统命令 ， 都以’.'开头
  .exit
  .quit
  .table 查看表
  .schema 查看表的结构
• sql语句， 都以‘;’结尾
  1-- 创建一张表
  create table stuinfo(id integer, name text, age integer, score float);
  2-- 插入一条记录
  insert into stuinfo values(1001, ‘zhangsan’, 18, 80);
  insert into stuinfo (id, name, score) values(1002, ‘lisi’, 90);
  3-- 查看数据库记录
  select * from stuinfo;
  select * from stuinfo where score = 80;
  select * from stuinfo where score = 80 and name= ‘zhangsan’;
  select * from stuinfo where score = 80 or name=‘wangwu’;
  select name,score from stuinfo; 查询指定的字段
  select * from stuinfo where score >= 85 and score < 90;
  4-- 删除一条记录
  delete from stuinfo where id=1003 and name=‘zhangsan’;
  5-- 更新一条记录
  update stuinfo set age=20 where id=1003;
  update stuinfo set age=30, score = 82 where id=1003;
  6-- 删除一张表
  drop table stuinfo;
  7-- 增加一列
  alter table stuinfo add column sex char;
  8-- 删除一列
  create table stu as select id, name, score from stuinfo;
  drop table stuinfo;
  alter table stu rename to stuinfo;
• 数据库设置主键：
  create table info(id integer primary key autoincrement, name vchar);
• sqlite3函数接口
• int sqlite3_open(
  const char filename, / Database filename (UTF-8) */
  sqlite3 *ppDb / OUT: SQLite db handle */
  );
  • 功能：打开数据库
  • 参数：filename 数据库名称
    ppdb 数据库句柄
  • 返回值：成功为0 SQLITE_OK ,出错 错误码
    int sqlite3_close(sqlite3* db);
  • 功能：关闭数据库
  • 参数：
  • 返回值：成功为0 SQLITE_OK ,出错 错误码
    const char sqlite3_errmsg(sqlite3db);
  • 功能：得到错误信息的描述
  • int sqlite3_exec(
    sqlite3* db, /* An open database /
    const char sql, / SQL to be evaluated /
    int (callback)(void arg,int,char,char**), /* Callback function /
    void * arg, / 1st argument to callback */
    char *errmsg / Error msg written here */
    );
• 功能：执行一条sql语句
• 参数：db 数据库句柄
  sql sql语句
  callback 回调函数，只有在查询时，才传参
  arg 为回调函数传递参数
  errmsg 错误消息
• 返回值：成功 SQLITE_OK
• 查询回调函数：
  int (callback)(void arg,int ncolumns ,char** f_value,char** f_name), /* Callback function */
• 功能：查询语句执行之后，会回调此函数
• 参数：arg 接收sqlite3_exec 传递来的参数
  ncolumns 列数
  f_value　列的值得地址
  f_name 列的名称
• 返回值：0，
• int sqlite3_get_table(
  sqlite3 db, / An open database */
  const char zSql, / SQL to be evaluated */
  char **pazResult, / Results of the query */
  int pnRow, / Number of result rows written here */
  int pnColumn, / Number of result columns written here */
  char *pzErrmsg / Error msg written here */
  );
  void sqlite3_free_table(char **result);
  查询
• 学生管理系统案例代码如下：

  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  #include <sqlite3.h>#define  DATABASE  "student.db"
  #define  N  128int do_insert(sqlite3 *db)
  {int id;char name[32] = {};char sex;int score;char sql[N] = {};char *errmsg;printf("Input id:");scanf("%d", &id);printf("Input name:");scanf("%s", name);getchar();printf("Input sex:");scanf("%c", &sex);printf("Input score:");scanf("%d", &score);sprintf(sql, "insert into stu values(%d, '%s', '%c', %d)", id, name, sex, score);if(sqlite3_exec(db, sql, NULL, NULL, &errmsg) != SQLITE_OK){printf("%s\n", errmsg);}else{printf("Insert done.\n");}return 0;
  }
  int do_delete(sqlite3 *db)
  {int id;char sql[N] = {};char *errmsg;printf("Input id:");scanf("%d", &id);sprintf(sql, "delete from stu where id = %d", id);if(sqlite3_exec(db, sql, NULL, NULL, &errmsg) != SQLITE_OK){printf("%s\n", errmsg);}else{printf("Delete done.\n");}return 0;
  }
  int do_update(sqlite3 *db)
  {int id;char sql[N] = {};char name[32] = "zhangsan";char *errmsg;printf("Input id:");scanf("%d", &id);sprintf(sql, "update stu set name='%s' where id=%d", name,id);if(sqlite3_exec(db, sql, NULL, NULL, &errmsg) != SQLITE_OK){printf("%s\n", errmsg);}else{printf("update done.\n");}return 0;
  }int callback(void *arg, int f_num, char ** f_value, char ** f_name)
  {int i = 0;for(i = 0; i < f_num; i++){//	printf("%-8s %s", f_value[i], f_name[i]);printf("%-8s", f_value[i]);}printf("++++++++++++++++++++++");putchar(10);return 0;
  }int do_query(sqlite3 *db)
  {char *errmsg;char sql[N] = "select count(*) from stu where name='zhangsan';";if(sqlite3_exec(db, sql, callback,NULL , &errmsg) != SQLITE_OK){printf("%s", errmsg);}else{printf("select done.\n");}
  }int do_query1(sqlite3 *db)
  {char *errmsg;char ** resultp;int nrow;int ncolumn;if(sqlite3_get_table(db, "select * from stu", &resultp, &nrow, &ncolumn, &errmsg) != SQLITE_OK){printf("%s\n", errmsg);return -1;}else{printf("query done.\n");}int i = 0;int j = 0;int index = ncolumn;for(j = 0; j < ncolumn; j++){printf("%-10s ", resultp[j]);}putchar(10);for(i = 0; i < nrow; i++){for(j = 0; j < ncolumn; j++){printf("%-10s ", resultp[index++]);}putchar(10);}return 0;
  }int main(int argc, const char *argv[])
  {sqlite3 *db;char *errmsg;int n;if(sqlite3_open(DATABASE, &db) != SQLITE_OK){printf("%s\n", sqlite3_errmsg(db));return -1;}else{printf("open DATABASE success.\n");}if(sqlite3_exec(db, "create table if not exists stu(id int, name char , sex char , score int);",NULL, NULL, &errmsg) != SQLITE_OK){printf("%s\n", errmsg);}else{printf("Create or open table success.\n");}while(1){printf("********************************************\n");printf("1: insert  2:query  3:delete 4:update 5:quit\n");printf("********************************************\n");printf("Please select:");scanf("%d", &n);switch(n){case 1:do_insert(db);break;case 2:do_query(db);//	do_query1(db);break;case 3:do_delete(db);break;case 4:do_update(db);break;case 5:printf("main exit.\n");sqlite3_close(db);exit(0);break;default :printf("Invalid data n.\n");}}return 0;
  }
  

  注：query1中的话为啥index++，因为API里面要把表头去掉，表结构如下：