如何检查C中的sqlite中是否存在记录

Question

我刚开始使用 sqlite，需要一些快速帮助。我有以下正在运行的代码。在最后一个查询中，即"Select * from company where id = 2". 我只想检查是否存在具有id = 2. 就是这样。但我不能那样做。回调方法对所有查询都是通用的，因此无法修改它，也不想为上次查询编写特定的回调。

我可以只获取0/1或False/True获取最后一个查询吗？我尝试过的是使用，计数行，但再次使用回调它打印结果而不是 0/1。

 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()
{
   sqlite3 *db;
   char *zErrMsg = 0;
   int rc;
   char *sql;

   /* Open database */
   rc = sqlite3_open("test.db", &db);
   if( rc ){
      fprintf(stderr, "Can't open database: %s\n", sqlite3_errmsg(db));
      exit(0);
   }else{
      fprintf(stderr, "Opened database successfully\n");
   }

   sql = "CREATE TABLE COMPANY("  \
         "ID INT PRIMARY KEY     NOT NULL," \
         "NAME           TEXT    NOT NULL," \
         "AGE            INT     NOT NULL," \
         "ADDRESS        CHAR(50)," \
         "SALARY         REAL );";

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

      /* Create SQL statement */
   sql = "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) "  \
         "VALUES (1, 'Paul', 32, 'California', 20000.00 ); " \
         "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) "  \
         "VALUES (2, 'Allen', 25, 'Texas', 15000.00 ); "     \
         "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)" \
         "VALUES (3, 'Teddy', 23, 'Norway', 20000.00 );" \
         "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)" \
         "VALUES (4, 'Mark', 25, 'Rich-Mond ', 65000.00 );";

   /* Execute SQL statement */
   rc = sqlite3_exec(db, sql, callback, 0, &zErrMsg);
   if( rc != SQLITE_OK ){
      fprintf(stderr, "SQL error: %s\n", zErrMsg);
      sqlite3_free(zErrMsg);
   }else{
      fprintf(stdout, "Records created successfully\n");
   }

   sql = "Select * from COMPANY where id = 2";

   rc = sqlite3_exec(db, sql, callback, 0, &zErrMsg);
   if( rc != SQLITE_OK ){
      fprintf(stderr, "SQL error: %s\n", zErrMsg);
      sqlite3_free(zErrMsg);
   }else{
      fprintf(stdout, "Records created successfully\n");
   }

   sqlite3_close(db);
   return 0;
}

Answer 1

You can exec your query differently

    sql = "Select * from COMPANY where id = 2";
    struct sqlite3_stmt *selectstmt;
    int result = sqlite3_prepare_v2(db, sql, -1, &selectstmt, NULL);
    if(result == SQLITE_OK)
    {
       if (sqlite3_step(selectstmt) == SQLITE_ROW)
       {
          // record found
       }
       else
       {
          // no record found
       }
    }
    sqlite3_finalize(selectstmt);