Question

所以我得到了这5个下拉，我需要用来从sql

中排序输出

现在我用

DropDownList_Instruktorer.Items.Insert(0, new ListItem("Vælg Instruktør", "*"));

对于默认值，我认为这将完成这项工作。但是

cmd.Parameters.addwithvalue

显然将值输入值而不是使用*来显示所有结果，就像通常在sql中一样

SqlCommand cmd = new SqlCommand(@"SELECT * FROM Hold 
                                            INNER JOIN Instruktorer
                                            ON instruktor_id = fk_in_id
                                            INNER JOIN Stilarter
                                            ON stilart_id = fk_st_id
                                            INNER JOIN  Aldersgruppe
                                            ON aldersgruppe_id = fk_ag_id
                                            INNER JOIN Niveauer
                                            ON niveau_id = fk_ni_id
                                            INNER JOIN Tider
                                            ON tid_id = fk_ht_id
                                            WHERE fk_in_id = @Instruktor AND
                                            fk_st_id = @Stilart AND
                                            fk_ag_id = @Aldersgruppe AND
                                            fk_ni_id = @Niveau AND
                                            fk_ht_id = @Tid", conn);
    cmd.Parameters.AddWithValue("@Instruktor", DropDownList_Instruktorer.SelectedValue);
    cmd.Parameters.AddWithValue("@Stilart", DropDownList_Stilart.SelectedValue);
    cmd.Parameters.AddWithValue("@Aldersgruppe", DropDownList_Aldersgrupper.SelectedValue);
    cmd.Parameters.AddWithValue("@Niveau", DropDownList_Niveauer.SelectedValue);
    cmd.Parameters.AddWithValue("@Tid", DropDownList_Tider.SelectedValue);

这是我的sql，我知道如何在不编写25条if语句的情况下让它工作吗？

Answer 1

为什么不使用字符串代替AddWithValue，例如：

string instructorStr = "";
string stilartStr = "";
...
if (DropDownList_Instruktorer.SelectedValue != "*")
{
    instructorStr = "fk_in_id = " + DropDownList_Instruktorer.SelectedValue + " AND";
}
if (DropDownList_Stilart.SelectedValue != "*")
{
    stilartStr = "fk_st_id = " + DropDownList_Stilart.SelectedValue + " AND";
}
...

SqlCommand cmd = new SqlCommand(@"SELECT * FROM Hold 
    INNER JOIN Instruktorer
    ON instruktor_id = fk_in_id
    INNER JOIN Stilarter
    ON stilart_id = fk_st_id
    INNER JOIN  Aldersgruppe
    ON aldersgruppe_id = fk_ag_id
    INNER JOIN Niveauer
    ON niveau_id = fk_ni_id
    INNER JOIN Tider
    ON tid_id = fk_ht_id
    WHERE " + 
    instructorStr + 
    stilartStr +
    ...
    + " 1 = 1", conn);

然后你可以选择用各个变量做各种各样的事情，包括ORDER BY

使用Stringbuilder会更干净，但更容易以这种方式显示它。

c＃多个下拉列表

1 个答案: