Sqlite - while (sqlite3_step(statement) == SQLITE_ROW) is not executing - ios

Question

I am trying to get the highest value in the Points column in my DB, however the sqlite_step statement never get executed.
This is the method with this in it.
+(NSMutableArray*)getMax {
[self databaseInit];
highScore *newMax = [[highScore alloc]init];
NSMutableArray *maxPointsArray = [[NSMutableArray alloc]init];
if (sqlite3_open(dbpath,&peopleDB)==SQLITE_OK)
{
NSString *selectMaxSQL = [NSString stringWithFormat:#"SELECT MAX POINTS FROM PEOPLE"];
if(sqlite3_prepare_v2(peopleDB, [selectMaxSQL UTF8String],-1,&statement, NULL)==SQLITE_OK){
while (sqlite3_step(statement) == SQLITE_ROW){
newMax.max = sqlite3_column_int(statement, 0);
}
[maxPointsArray addObject:newMax];
}
}
sqlite3_finalize(statement);
sqlite3_close(peopleDB);
return maxPointsArray;
}
If it makes a difference the databaseInit method is -
+(void)databaseInit {
//get documents directory
dirPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
docsDir = dirPaths [0];
//create path to database file
databasePath = [[NSString alloc]initWithString:[docsDir stringByAppendingPathComponent:#"people.db"]];
dbpath = [databasePath UTF8String];
}
Any help with this would be hugely appreciated, let me know if any more code is needed.

Answer 1

It is not executed because your query is wrong.
Assuming that points is a field of your people table, the query should be:
SELECT MAX(points) FROM people

Answer 2

You have the immediate answer, but the long term solution is to log sqlite3_errmsg if any SQLite functions fail. The way your code is written, you have no way of knowing which of the calls failed and why.
Thus, you may want:
+(NSMutableArray*)getMax {
int rc;
[self databaseInit];
highScore *newMax = [[highScore alloc]init];
NSMutableArray *maxPointsArray = [[NSMutableArray alloc]init];
if ((rc = sqlite3_open(dbpath, &peopleDB)) == SQLITE_OK) {
const char *selectMaxSQL = "SELECT MAX(POINTS) FROM PEOPLE";
if(sqlite3_prepare_v2(peopleDB, selectMaxSQL, -1, &statement, NULL)==SQLITE_OK){
if ((rc = sqlite3_step(statement)) == SQLITE_ROW){
newMax.max = sqlite3_column_int(statement, 0);
[maxPointsArray addObject:newMax];
} else {
if (rc == SQLITE_DONE) {
NSLog(#"No record returned");
} else {
NSLog(#"Step failed %s (%d)", sqlite3_errmsg(peopleDB), rc);
}
}
sqlite3_finalize(statement);
} else {
NSLog(#"Prepare failed %s (%d)", sqlite3_errmsg(peopleDB), rc);
}
} else {
NSLog(#"Open failed %d", rc);
}
sqlite3_close(peopleDB);
return maxPointsArray;
}
If you had done this with your original SQL, it would have reported precisely where in the SQL it encountered the error. Furthermore, if you have any problems in the future, this sort of defensive programming will help diagnose problems more quickly.
It's also worth noting that it's generally recommended not to open and close the database with every database call, but rather to open the database only once. It's more efficient and people have reported problems when constantly opening and closing databases.