Fmdb 选择带有变量表名的查询

Posted 2023-03-08

【中文标题】Fmdb 选择带有变量表名的查询

【英文标题】：Fmdb Select query with variable table name

【发布时间】：2013-09-30 13:28:03

【问题描述】：

我想从不同的表中获取结果，表是由用户选择的。所以，我使用表名作为变量，但它返回 nil 查询。

FMResultSet *query = [db1 executeQuery:@"SELECT Image, Explanation FROM %@ WHERE Image !='empty'"
"UNION SELECT Image, Explanation FROM %@ WHERE Image !='empty'"
"UNION SELECT Image, Explanation FROM %@ WHERE Image !='empty'"
"UNION SELECT Image, Explanation FROM %@ WHERE Image !='empty'"
"UNION SELECT Image, Explanation FROM %@ WHERE Image !='empty'"
"UNION SELECT Image, Explanation FROM %@ WHERE Image !='empty'", [NSString stringWithFormat:@"%@1",tableName], [NSString stringWithFormat:@"%@2",tableName],
[NSString stringWithFormat:@"%@3",tableName], [NSString stringWithFormat:@"%@4",tableName], [NSString stringWithFormat:@"%@5",tableName], [NSString stringWithFormat:@"%@6",tableName]];

如果我硬编码表名，它会返回数据。

FMResultSet *query = [db1 executeQuery:
@"SELECT Image, Explanation FROM Class1 WHERE Image !='empty'"
"UNION SELECT Image, Explanation FROM Class2 WHERE Image !='empty'"
"UNION SELECT Image, Explanation FROM Class3 WHERE Image !='empty'"
"UNION SELECT Image, Explanation FROM Class4 WHERE Image !='empty'"
"UNION SELECT Image, Explanation FROM Class5 WHERE Image !='empty'"
"UNION SELECT Image, Explanation FROM Class6 WHERE Image !='empty'"];

我记录了 tableName 值，它返回了正确的值，即“Class”。 请帮我解决这个问题，并为此目的提出最佳查询。

【参考方案1】：

使用此代码：

FMResultSet *query = [db1 executeQuery:[NSString stringWithFormat:@"SELECT Image, Explanation FROM %@ WHERE Image !='empty'"
"UNION SELECT Image, Explanation FROM %@ WHERE Image !='empty'"
"UNION SELECT Image, Explanation FROM %@ WHERE Image !='empty'"
"UNION SELECT Image, Explanation FROM %@ WHERE Image !='empty'"
"UNION SELECT Image, Explanation FROM %@ WHERE Image !='empty'"
"UNION SELECT Image, Explanation FROM %@ WHERE Image !='empty'", [NSString stringWithFormat:@"%@1",tableName], [NSString stringWithFormat:@"%@2",tableName],
[NSString stringWithFormat:@"%@3",tableName], [NSString stringWithFormat:@"%@4",tableName], [NSString stringWithFormat:@"%@5",tableName], [NSString stringWithFormat:@"%@6",tableName]]];

【讨论】：

谢谢@Vin。这是为此目的的正确/优化查询吗？