[英]How can i select from more than one table in a SqlDataSource asp.net
[英]Can I SELECT more than one value from the same column
我正在尝试使用单个MySql.Data
SELECT
语句从多行获取值。
我尝试使用以下代码但失败了。 错误说
第 # 行存在语法错误
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();
您可以像这样简单地使用in
运算符,而不是重复使用无效的Select
语句:
SELECT value
FROM metatable
WHERE ProductID = 16 AND MetaKey in ('SKU','Price', 'Sold', 'SoldDate')
而且你不需要在 where 后面加上括号。
您可以将查询修改为 UNION 所有输出,如下所示。 Union 组合了 2 个或更多查询的结果(确保您有相同顺序的相似列)
MySqlConnection mysqlcon = new MySqlConnection(M_str_sqlcon);
MySqlCommand mysqlcom = new MySqlCommand(
"SELECT value FROM metatable WHERE(ProductID = 16 AND MetaKey = 'SKU') UNION " +
"SELECT value FROM metatable WHERE(ProductID = 16 AND MetaKey = 'Price') UNION " +
"SELECT value FROM metatable WHERE(ProductID = 16 AND MetaKey = 'Sold') UNION " +
"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();
但是,由于您是从本示例中的同一个表中提取数据,因此您可以使用 OR 组合以下条件:
MySqlConnection mysqlcon = new MySqlConnection(M_str_sqlcon);
MySqlCommand mysqlcom = new MySqlCommand(
"SELECT value FROM metatable WHERE(ProductID = 16 AND MetaKey = 'SKU') OR (ProductID = 16 AND MetaKey = 'Price') OR (ProductID = 16 AND MetaKey = 'Sold') OR (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();
或者您可以使用 IN 运算符,如下所示:
MySqlConnection mysqlcon = new MySqlConnection(M_str_sqlcon);
MySqlCommand mysqlcom = new MySqlCommand(
"SELECT value FROM metatable WHERE ProductID = 16 AND MetaKey IN ('SKU','Price','Sold','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();
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