ios - 随机选择、不重复的Sql语句

Question

我在 iOS 上使用 sqlite 数据库创建了一个问答游戏。我可以随机检索我的问题及其正确答案，但我有两个问题。首先我想知道是否可以不重复同样的问题？其次，我希望玩家设置他想要玩的问题数量。对于第二个，我成功创建了一个带有文本字段的警报 View ，但是是否可以将值传递到 sql 语句中？预先感谢您。

这是我用于随机问题的 sql 语句的代码:

const char *sql = "SELECT * FROM Questions WHERE Category IS 2 ORDER BY RANDOM() LIMIT 1";

所有代码是:

-(NSMutableArray *) categoriesList{
categories = [[NSMutableArray alloc] initWithCapacity:10];
@try {
    NSFileManager *fileMgr = [NSFileManager defaultManager];
    NSString *dbPath = [[[NSBundle mainBundle] resourcePath ]stringByAppendingPathComponent:@"Categories.sqlite"];
    BOOL success = [fileMgr fileExistsAtPath:dbPath];
    if(!success)
    {
        NSLog(@"Cannot locate database file '%@'.", dbPath);
    }
    if(!(sqlite3_open([dbPath UTF8String], &db) == SQLITE_OK))
    {
        NSLog(@"An error has occured: %s", sqlite3_errmsg(db));
    }


    const char *sql = "SELECT * FROM Questions WHERE Category IS 2 ORDER BY RANDOM() LIMIT 1";
    sqlite3_stmt *sqlStatement;
    NSString * insertSQL = [NSString stringWithFormat:
                            @"UPDATE Questions SET Used='NO'"];
    const char * insert_stmt = [insertSQL UTF8String];
    sqlite3_prepare_v2(db, insert_stmt,-1, &sqlStatement, NULL);

    if(sqlite3_prepare(db, sql, -1, &sqlStatement, NULL) != SQLITE_OK)
    {
        NSLog(@"Problem with prepare statement:  %s", sqlite3_errmsg(db));
    }else{

        while (sqlite3_step(sqlStatement)==SQLITE_ROW) {

            Categories * choise = [[Categories alloc] init];

            question.text = [NSString stringWithUTF8String:(char *) sqlite3_column_text(sqlStatement, 1)];

            NSMutableArray  *arary = [[NSMutableArray alloc]init];
            while (arary.count < 4) {
                int value = arc4random()%4+2;
                BOOL isFound = [[arary filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:[NSString stringWithFormat:@"intValue == %d",value]]] count];
                if(!isFound)
                    [arary addObject:[NSNumber numberWithInteger:value]];
            }
            answer1.text = [NSString stringWithUTF8String:(char *) sqlite3_column_text(sqlStatement, [[arary objectAtIndex:0] intValue])];
            answer2.text = [NSString stringWithUTF8String:(char *) sqlite3_column_text(sqlStatement, [[arary objectAtIndex:1] intValue])];
            answer3.text = [NSString stringWithUTF8String:(char *) sqlite3_column_text(sqlStatement, [[arary objectAtIndex:2] intValue])];
            answer4.text = [NSString stringWithUTF8String:(char *) sqlite3_column_text(sqlStatement, [[arary objectAtIndex:3] intValue])];

            NSString * columnName  = [NSString stringWithUTF8String:(char *) sqlite3_column_name(sqlStatement, [[arary objectAtIndex:0] intValue])];

            answer1.tag = ([columnName isEqualToString:@"Answer1"])?999:0;

            columnName = [NSString stringWithUTF8String:(char *) sqlite3_column_name(sqlStatement, [[arary objectAtIndex:1] intValue])];

            answer2.tag = ([columnName isEqualToString:@"Answer1"])?999:0;


            columnName = [NSString stringWithUTF8String:(char *) sqlite3_column_name(sqlStatement, [[arary objectAtIndex:2] intValue])];

            answer3.tag = ([columnName isEqualToString:@"Answer1"])?999:0;


            columnName = [NSString stringWithUTF8String:(char *) sqlite3_column_name(sqlStatement, [[arary objectAtIndex:3] intValue])];

            answer4.tag = ([columnName isEqualToString:@"Answer1"])?999:0;

            answer1btn.tag = answer1.tag;
            answer2btn.tag = answer2.tag;
            answer3btn.tag = answer3.tag;
            answer4btn.tag = answer4.tag;
            [categories addObject:choise];
            [self prepareForIntroAnimation];
            [self performIntroAnimation];
        }
    }
    sqlite3_finalize(sqlStatement);
}
@catch (NSException *exception) {
    NSLog(@"Problem with prepare statement:  %s", sqlite3_errmsg(db));
}
@finally {

    sqlite3_close(db);

    return categories;
}
}

Answer 1

1. 您可以做的是添加一个列，让它对已使用的表示 YES，对未使用的表示 NO，然后修改您的 SQL 语句以表示 where used=NO 或类似的内容。

2. 您可以使用字符串并将值传递到字符串中，然后将其转换为字符:

   NSString *sqlStr = [NSString stringWithFormat:@"SELECT * FROM Questions WHERE Category IS 2 ORDER BY RANDOM() LIMIT %i", [limitTextfield.text intValue]];
   
   const char *sqlChar = [sqlStr UTF8String];
   

编辑

回答您的评论。在 viewDidLoad 中，您可以使用

将整个“已使用”列设置为“否”

UPDATE Questions
SET used = 'NO'
WHERE used = 'YES';

这样会将列中“YES”部分的所有元素重置为默认值“NO”

NSString *sqlStr = [NSString stringWithFormat:@"UPDATE Questions SELECT * FROM Questions WHERE questionColumn = '%@' SET used = 'YES'", questionLabel.text intValue];
const char *sqlChar = [sqlStr UTF8String];