不能使用空对象或列名.必要时使用单独的空格

在此代码中:

string sql = "SELECT * FROM rd_main WHERE manifest!='"'" AND manifest IS NOT NULL";
string tableName = "rd_main";
conn.Open();
SqlDataAdapter da = new SqlDataAdapter(sql, conn);
DataSet ds = new DataSet();
da.Fill(ds, tableName);

我一直得到:

Cannot use empty object or column names. Use a single space if necessary.

fill(…)

I have try:

SELECT rd_main.* FROM rd_main WHERE rd_main.manifest<>"" AND rd_main.manifest IS NOT NULL

我做错了什么?

string sql = "SELECT * FROM rd_main WHERE manifest!='' AND manifest IS NOT NULL";