Question

I have an SQLite database in my iOS application. I’m trying to use the SQL function MAX()

- (void) getMaxTime {

if (sqlite3_open([databasePath UTF8String], &timingsDatabase) == SQLITE_OK) 
{
    NSString *maxTimeStatement = [NSString stringWithFormat:@" SELECT max(NUMBERS) FROM TIMINGS"];
    sqlite3_stmt *statement;
    if(sqlite3_prepare_v2(timingsDatabase, [maxTimeStatement UTF8String], -1, &statement, nil) == SQLITE_OK){
        while (sqlite3_step(statement) == SQLITE_ROW) {
            massimo = sqlite3_column_int(statement, 0);

            NSLog(@"The maximun time is %d seconds ", massimo);
        } 
        sqlite3_finalize(statement);
        sqlite3_close(timingsDatabase);     
    }      
}

All the numbers in the column NUMBERS have 6 digits after the coma.
Everything works fine if all the numbers are > 10 or all the numbers are <10.

But (example) when I try to get the max among:

• 1.339670
• 2.955537
• 11.355558

It prints: “The maximun time is 2 seconds” (instead of 11)! I’m struggling to understand why.

*EDIT

This is how my Database was created:

-(void)createDatabase 
{
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];

    databasePath = [[NSString alloc]initWithString:[documentsDirectory stringByAppendingPathComponent:@"timings.db"]];

    if ([[NSFileManager defaultManager] fileExistsAtPath:databasePath] == FALSE)
    {
        if (sqlite3_open([databasePath UTF8String], &timingsDatabase) == SQLITE_OK)
        {
            const char *sqlStatement = "CREATE TABLE IF NOT EXISTS TIMINGS (ID INTEGER PRIMARY KEY AUTOINCREMENT, TIMESTAMP TEXT, TIMING TEXT, NUMBERS TEXT)";
            char *error;
            sqlite3_exec(timingsDatabase, sqlStatement, NULL, NULL, &error);
            sqlite3_close(timingsDatabase);
        }
    }
}

And this is how timings are stored:

-(void)storeTiming 
{
    if (sqlite3_open([databasePath UTF8String], &timingsDatabase) == SQLITE_OK)
    {
        NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
        [dateFormatter setDateFormat:@"HH:mm:ss.SSS"];

        NSString *insertStatement = [NSString stringWithFormat:@"INSERT INTO TIMINGS (TIMESTAMP, TIMING, NUMBERS) VALUES (\"%@\", \"%@\", \"%f\")", [dateFormatter stringFromDate:startDate], stopWatchLabel.text , intervallo] ;


        char *error;
        sqlite3_exec(timingsDatabase, [insertStatement UTF8String], NULL, NULL, &error);
        sqlite3_close(timingsDatabase);
    }
} 

Answer 1

Seems that column’s data type is string… You should change it to float to use MAX() function.