查询具有未知数量参数的数据库

Question

我试图查询现有的访问数据库并允许用户为WHERE子句选择多个值。我一直在使用此代码对用户马克布拉克特本网站礼貌发现：

string[] tags = new string[] { "ruby", "rails", "scruffy", "rubyonrails" }; 
string cmdText = "SELECT * FROM Tags WHERE Name IN ({0})"; 

string[] paramNames = tags.Select(
    (s, i) => "@tag" + i.ToString() 
).ToArray(); 

string inClause = string.Join(",", paramNames); 
using (SqlCommand cmd = new SqlCommand(string.Format(cmdText, inClause))) { 
    for(int i = 0; i < paramNames.Length; i++) { 
     cmd.Parameters.AddWithValue(paramNames[i], tags[i]); 
    } 
} 

其中给出了这样的：

cmd.CommandText = "SELECT * FROM Tags WHERE Name IN (@tag0,@tag1,@tag2,@tag3)" 
cmd.Parameters["@tag0"] = "ruby" 
cmd.Parameters["@tag1"] = "rails" 
cmd.Parameters["@tag2"] = "scruffy" 
cmd.Parameters["@tag3"] = "rubyonrails" 

这工作出色，但我想下面的功能良好。如果用户决定不输入任何值（在本例中，如果标签数组为空），那么我希望返回所有结果。有效地只是一个SELECT * FROM标签。

Answer 1

如何像

string[] tags = new string[] { "ruby", "rails", "scruffy", "rubyonrails" }; 
string cmdText = "SELECT * FROM Tags {0}"; 

string[] paramNames = tags.Select(
      (s, i) => "@tag" + i.ToString() 
     ).ToArray(); 

string cmdWhere = paramNames.Length > 0 ? String.Format("WHERE Name IN ({0})", string.Join(",", paramNames)) : ""; 
using (SqlCommand cmd = new SqlCommand(string.Format(cmdText, cmdWhere))) 
{ 
    for (int i = 0; i < paramNames.Length; i++) 
    { 
     cmd.Parameters.AddWithValue(paramNames[i], tags[i]); 
    } 
} 

因此，如果你没有参数，你在末尾没有添加where子句。

Answer 2

放在哪里子句的变量中，使的CommandText像cmd.CommandText = SELECT + WHERE 时：SELECT = "SELECT * FROM Tags" WHERE = "WHERE " + "Name IN (@tag0 ....)" 如果没有参数变量会在哪里=“”

Answer 3

尝试为

string[] tags = new string[] { "ruby", "rails", "scruffy", "rubyonrails" }; 
string cmdText = "SELECT * FROM Tags" ; 

string cond=" WHERE Name IN ({0})"; 

string[] paramNames = tags.Select(
    (s, i) => "@tag" + i.ToString() 
).ToArray(); 

if(paramNames.Length>0){ 
    string inClause = string.Join(",", paramNames); 
    cmdText=string.Concat(cmdText,string.Format(cond, inClause)); 
} 
using (SqlCommand cmd = new SqlCommand(cmdText) { 
    for(int i = 0; i < paramNames.Length; i++) { 
     cmd.Parameters.AddWithValue(paramNames[i], tags[i]); 
    } 
} 

Answer 4

而不是每个项目一个参数，为什么不将它们连接起来？

我不知道这是否会在MS Access工作，但这里是我使用的MS SQL：

DECLARE @tagIds nvarchar(max) 

SELECT * FROM Tags where @tagIds is null or tagId IN (select number from dbo.iter_intlist_to_tbl(@tagIds)) 

所以@tagIds是一个逗号分隔的编号清单，我只是用函数解析它。如果@tagIds为空，则返回所有标记。

的iter_intlist_to_tbl()功能如下：

CREATE FUNCTION [dbo].[iter_intlist_to_tbl] (@list nvarchar(MAX)) 
    RETURNS @tbl TABLE (listpos int IDENTITY(1, 1) NOT NULL, 
         number int NOT NULL) AS 
BEGIN 
    DECLARE @startpos int, 
      @endpos int, 
      @textpos int, 
      @chunklen smallint, 
      @str  nvarchar(4000), 
      @tmpstr nvarchar(4000), 
      @leftover nvarchar(4000) 

    SET @textpos = 1 
    SET @leftover = '' 
    WHILE @textpos <= datalength(@list)/2 
    BEGIN 
     SET @chunklen = 4000 - datalength(@leftover)/2 
     SET @tmpstr = ltrim(@leftover + 
        substring(@list, @textpos, @chunklen)) 
     SET @textpos = @textpos + @chunklen 

     SET @startpos = 0 
     SET @endpos = charindex(',' COLLATE database_default, @tmpstr) 

     WHILE @endpos > 0 
     BEGIN 
     SET @str = substring(@tmpstr, @startpos + 1, 
           @endpos - @startpos - 1) 
     IF @str <> '' 
      INSERT @tbl (number) VALUES(convert(int, @str)) 
     SET @startpos = @endpos 
     SET @endpos = charindex(',' COLLATE database_default, 
           @tmpstr, @startpos + 1) 
     END 

     SET @leftover = right(@tmpstr, datalength(@tmpstr)/2 - @startpos) 
    END 

    IF ltrim(rtrim(@leftover)) <> '' 
     INSERT @tbl (number) VALUES(convert(int, @leftover)) 

    RETURN 
END 
GO 

对分析逗号分隔列表的详细信息，请参阅http://www.sommarskog.se/arrays-in-sql-2005.html。虽然我想你会在MS Access不同的方法来做这

Answer 5

我认为，如果任何标签的为空

if (@tag0 is null or @tag1 is null or @tag2 is null or @tag3 is null) 
begin 
    select * from tags 
end 
else 
    begin 
    SELECT * FROM Tags WHERE Name IN (@tag0,@tag1,@tag2,@tag3) 
end 

Answer 6

我已经修改了我现有的。这将工作。

string cmdText = "SELECT * FROM Tags "; 
     string[] tags = new string[] { "ruby", "rails", "scruffy", "rubyonrails" }; 
     string where = null; 
     if (tags != null) 
     { 
      where = "WHERE Name IN ("; 
      foreach (string tag in tags) 
      { 
       where += "'" + tag + "',"; 
      } 
      where = where.TrimEnd(',') + ")"; 
     } 
     if (!string.IsNullOrEmpty(where)) 
     { 
      cmdText += where; 
     }