Question

我不确定这是否属实，但我被告知FMDatabase如果你这样做会表现更好

NSString *query = [NSString stringWithFormat:@"SELECT * FROM db where col=?"];
FMResultSet *rs = [theDatabase executeQuery:query, columnToLookFor];

vs

NSString *query = [NSString stringWithFormat:@"SELECT * FROM db where col='columnToLookFor'"];
FMResultSet *rs = [theDataBase executeQuery:query];

所以我们有一个搜索查询来执行此操作：

NSString *query = [NSString stringWithFormat:@"SELECT Symbol, Category FROM Symbols where Category like \"%%%@%%\" or Symbol like \"%%%@%%\" group by Symbol, Category order by Category", searchtext, searchtext];
FMResultSet *rs = [theDatabase executeQuery:query];

我正在尝试将其更改为：

NSString *query = [NSString stringWithFormat:@"SELECT Symbol, Category FROM Symbols where Category like \"%%?%%\" or Symbol like \"%%?%%\" group by Symbol, Category order by Category"];
FMResultSet *rs = [theDatabase executeQuery:query, searchtext, searchtext];

然而在带有？的第二种形式中，我的FMResultSet为0，我不确定在这种情况下我做错了什么。这会加速我们的搜索吗？或者这个功能花费这么长时间的数据库设计更糟糕。

Answer 1

假设你的第一个中的searchtext变量是一个问号，那么没有理由为什么一个会工作而另一个不起作用，因为你把这个文字放在第二个的SQL字符串中。您可能希望将两行更改为：

NSString *query = [NSString stringWithString:@"SELECT Symbol, Category FROM Symbols where Category like '%%?%%' or Symbol like '%%?%%' group by Symbol, Category order by Category"];
FMResultSet *rs = [theDatabase executeQuery:query];

此外，我会在行之前执行此操作，以查看在FMDB处理SQL时的样子：

[theDatabase setTraceExecution:YES];

编辑：尝试将其更改为此并查看跟踪执行的内容：

NSString *query = [NSString stringWithString:@"SELECT Symbol, Category FROM Symbols where Category like '%%?%%' or Symbol like '%%?%%' group by Symbol, Category order by Category"];
FMResultSet *rs = [theDatabase executeQuery:query, searchtext, searchtext, nil];

Answer 2

FMResultSet *result = [db executeQuery: @"SELECT * FROM channels_list WHERE type = 'person' AND members LIKE (?)",[NSString stringWithFormat:@"%%%@%%", userID]];

在FMDatabase for iOS中使用LIKE“％something％”

2 个答案: