c# - 我可以从同一列中选择多个值吗

Question

我正在尝试使用单个 MySql.Data SELECT 语句从多个行中获取值。

我尝试使用以下代码但失败了。错误说

there is a syntax error on line #

MySqlConnection mysqlcon = new MySqlConnection(M_str_sqlcon);

MySqlCommand mysqlcom = new MySqlCommand(
    "SELECT value FROM metatable WHERE(ProductID = 16 AND MetaKey = 'SKU') AND " +
    "SELECT value FROM metatable WHERE(ProductID = 16 AND MetaKey = 'Price') AND " +
    "SELECT value FROM metatable WHERE(ProductID = 16 AND MetaKey = 'Sold') AND " +
    "SELECT value FROM metatable WHERE(ProductID = 16 AND MetaKey = 'SoldDate')"
, mysqlcon);

MySqlDataReader r = mysqlcom.ExecuteReader(CommandBehavior.CloseConnection);

prodMeta.Add(new ProductMeta{
    ProductSKU = r.GetString(0),
    RegularPrice = r.GetDouble(1),
    SoldCount = r.GetInt32(2),
    SoldDate = r.GetString(3)
});

mysqlcon.Close();

Answer 1

与其重复无效的 Select 语句，您可以简单地使用 in像这样的运算符:

SELECT value 
FROM metatable 
WHERE ProductID = 16 AND MetaKey in ('SKU','Price', 'Sold', 'SoldDate')

而且您不需要 where 后面的括号。