从iPhone ios中的sqlite数据库中获取行数

Question

背景

我一整天都试图解决问题,我阅读了我可以在互联网上找到的所有文章和文档,但我无法解决这个问题.我正在为iPhone编写应用程序,我需要使用sqlite数据库(sqlite3).

主要问题

我已经创建了我的数据库,一切都很顺利,直到我想要计算表中的行数.表名是ARTICLES,所以我写道

SELECT COUNT(*) FROM ARTICLES

我的程序什么都不做,并在日志中写入:未知错误.

const char *query = "SELECT COUNT (*) FROM ARTICLES";
sqlite3_stmt *compiledQuery;
sqlite3_prepare_v2(database, query, -1, &compiledQuery, NULL);

程序在上面的代码中给出消息" 未知错误 ",我无法获得行数.谁能帮我解决这个问题...或者可能是sqlite的东西不正确？

码

- (int) GetArticlesCount
{
    if (sqlite3_open([self.dataBasePath UTF8String], &articlesDB) == SQLITE_OK)
    {
        const char* sqlStatement = "SELECT COUNT(*) FROM ARTICLES";
        sqlite3_stmt *statement;

        if( sqlite3_prepare_v2(articlesDB, sqlStatement, -1, &statement, NULL) == SQLITE_OK )
        {
            if( sqlite3_step(statement) == SQLITE_DONE )
            {

            }
            else
            {
                NSLog( @"Failed from sqlite3_step. Error is:  %s", sqlite3_errmsg(articlesDB) );
            }
        }
        else
        {
            NSLog( @"Failed from sqlite3_prepare_v2. Error is:  %s", sqlite3_errmsg(articlesDB) );
        }

        // Finalize and close database.
        sqlite3_finalize(statement);
        sqlite3_close(articlesDB);
    }

    return 0;
}

在此行中出现未知错误:

NSLog( @"Failed from sqlite3_step. Error is:  %s", sqlite3_errmsg(articlesDB) );

我必须添加什么代码或我必须做什么来获得行数？请帮忙...

工作守则(无效)

const char* sqlStatement = "SELECT * FROM ARTICLES";
sqlite3_stmt *statement;
if( sqlite3_prepare_v2(articlesDB, sqlStatement, -1, &statement, NULL) == SQLITE_OK )
{
    int count = 0;
    while( sqlite3_step(statement) == SQLITE_ROW )
        count++;
}

我得到正确的行数!但我不认为这是一种有效的方法......我认为sqlite的东西不对...

Answer 1

感谢您的更新,我相信问题是您的检查SQLITE_DONE而不是SQLITE_ROW,所以我已更新您的方法如下:

- (int)getArticlesCount {
  int count = 0;
  if (sqlite3_open([self.dataBasePath UTF8String], &articlesDB) ==
      SQLITE_OK) {
    const char* sqlStatement = "SELECT COUNT(*) FROM ARTICLES";
    sqlite3_stmt *statement;

    if (sqlite3_prepare_v2(articlesDB, sqlStatement, -1, &statement, NULL) ==
        SQLITE_OK) {
      // Loop through all the returned rows (should be just one)
      while(sqlite3_step(statement) == SQLITE_ROW) {
        count = sqlite3_column_int(statement, 0);
      }
    } else {
        NSLog(@"Failed from sqlite3_prepare_v2. Error is:  %s",
              sqlite3_errmsg(articlesDB));
    }

    // Finalize and close database.
    sqlite3_finalize(statement);
    sqlite3_close(articlesDB);
  }

  return count;
}