ios - 选择所有如果 blah.. 否则选择所有 blah

Question

我有一个像这样的枚举:

typedef NS_ENUM(int, name) {
    kAll,
    kFirstType,
    kSecondType
};

然后我做:

if (type == kAll) {
        query = [NSString stringWithFormat:@"SELECT * FROM TABLE WHERE ID = %ld", itemID];
    }
    else {
        query = [NSString stringWithFormat:@"SELECT * FROM TABLE WHERE ID = %ld AND type = %ld", itemID, type];
    }

我如何将其组合成一个查询，例如:

"SELECT CASE WHEN type = 0 THEN (SELECT ALL ITEMS) ELSE '* WHERE ID = blah AND type = meh' END;

我如何通过查询来做到这一点？我不想要 if (blah) then query = meh.. else query = other..

Answer 1

你可以这样做:

select * from myTable where id = :id and (:type = 0 or :type = type)

或者这个:

select * from myTable where id = ? and (? in (0, type))

但我不希望第二个特别表现良好。我还没有测试过任何一个版本。

无法从语句中更改 WHERE 子句的结构。您需要某种 eval 函数，它不是 SQLite 内置的。您可以找到可加载的 eval 扩展的源代码 in the SQLite source tree如果你愿意，但这似乎有点矫枉过正。