从 iPhone ios 中的 sqlite 数据库获取行数 [英] Get Rows Count from sqlite database in iPhone ios

问题描述

我一整天都在试图解决一个问题，我阅读了互联网上可以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).

All day long I've been trying to solve a problem, I read all the articles and documentation that I could find on the Internet, but I can't solve this. I'm writing an application for iPhone and I need to work with a sqlite database (sqlite3).

我已经创建了我的数据库并且一切顺利，直到我想获得表中的行数.表名是ARTICLES，所以我写了

I have created my database and all is going good until I wanted to get a count of the rows in my table. The Table name is ARTICLES, so I wrote

SELECT COUNT(*) FROM ARTICLES

我的程序什么都不做，而是在日志中写入:未知错误.

My program does nothing and writes in the log: Unknown Error.

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

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

Program gives message "Unknown Error" in the above code, and I can't get the count of rows. Who can help me to solve this problem... or may be something with sqlite is not correct?

- (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;
}

在这一行中出现了未知错误:

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

我必须在代码中添加什么或我必须做什么才能获得行数?请帮忙...

What must I add to the code or what must I do to get the count of rows? Please help...

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++;
}

我得到了正确的行数！但我不认为这是一个有效的方法......我认为sqlite的东西不正确......

I get the right count of rows! But I don't think it is an effective method... I think that something with sqlite is not going right...

推荐答案

感谢您的更新，我相信问题在于您检查的是 SQLITE_DONE 而不是 SQLITE_ROW，所以我在下面更新了你的方法:

Thank you for the update, I believe the problem is your check against SQLITE_DONE instead of SQLITE_ROW, so I have updated your method below:

- (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;
}

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