用字符串变量查询字符串串联

Question

我在这个查询中有一个问题， country是一个变量。 错误：国家是无效的列名..

cmd.CommandText = "SELECT [news_id], [news_title] from [upload_news] WHERE [city]="+ country; 

Answer 1

尝试：

"SELECT [news_id], [news_title] from [upload_news] WHERE [city]='"+ country +"'"; 

然而指示正确的方式做添加条件SELECT语句中使用一个变量：

cmd.CommandText = "SELECT [news_id], [news_title] from [upload_news] WHERE [city]=@param" 
cmd.Parameters.AddWithValue("param", country); 

PS：您的第一次尝试不起作用，因为您正在执行的实际SQL会：

SELECT [news_id], [news_title] from [upload_news] WHERE [city] = USA 

VS

SELECT [news_id], [news_title] from [upload_news] WHERE [city] = 'USA'