Question

我试图从MySQL获取一些值 - 列为行，反之亦然 - 在DataGridView上显示。我有这个代码，应该在MySQL-

中运行

SET @header = CONCAT('SELECT \'sl\', ',
    (SELECT GROUP_CONCAT(CONCAT(' \'', sl, '\'')) FROM cars where sl=1),
    ' LIMIT 0, 0');

SET @a = -1;
SET @line1 = CONCAT(
    'SELECT \'Plate\',',
    (
        SELECT GROUP_CONCAT(
            CONCAT(' (SELECT Plate FROM cars LIMIT ',
                @a:=@a+1,
                ', 1)')
            )
        FROM cars where sl=1
    ));

SET @a := -1;
SET @line2 = CONCAT(
    'SELECT \'Brand\',',
    (
        SELECT GROUP_CONCAT(
            CONCAT(' (SELECT Brand FROM cars LIMIT ',
                @a:=@a+1,
                ', 1)')
            )
        FROM cars where sl=1
    ));

SET @query = CONCAT('(',
    @header,
    ') UNION (',
    @line1,
    ') UNION (',
    @line2,
    ')'
);

PREPARE my_query FROM @query;
EXECUTE my_query;

现在，当我尝试通过ExecuteNonQuery命令运行此操作时，将所有这些代码保存在字符串中，我收到MySQLException错误 - Fatal error encountered during command execution.

我试图将代码拆分为单独的字符串，但会弹出相同的错误。还尝试增加CommandTimeout，但没有任何效果。

有没有特殊的方法来运行这些语句？或者代码有问题吗？请注意，这在命令行客户端上没有任何错误的情况下有效运行。

PS：代码用于Q＃3288014 - 感谢Anax

编辑：

我找到了同样的工作，但都在VB中完成。

Dim sa() As String = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
Dim sa2() As String = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
connect()
Dim reader As MySqlDataReader
execstr = "describe cars"
Dim cmd As New MySqlCommand(execstr, connection)
reader = cmd.ExecuteReader()
Dim i As Integer = 0
While reader.Read
    sa(i) = reader.GetString(0)
    i = i + 1
End While
reader.Close()
connection.Close()
connect()
execstr = "select*from cars where sl=1;"
Dim cmd2 As New MySqlCommand(execstr, connection)
reader = cmd2.ExecuteReader()
While reader.Read
   For i1 As Integer = 0 To sa.Length - 1
        sa2(i1) = reader.GetString(i1)
   Next
End While
reader.Close()
connection.Close()
reader.Close()
connection.Close()
Dim t As New DataTable
t.Columns.Add(sa(0))
t.Columns.Add(sa2(0))
For y As Integer = 1 To sa.Length - 1
    t.Rows.Add(sa(y), sa2(y))
Next
DataGridView1.DataSource = t

有趣地发现，在MySQL中的字符串中可以完成所有操作，在VB中需要这么多代码。

Answer 1

您无法在单个或一系列ExecuteNonQuery命令中执行此操作。这个例子显示了你将放在mysql上的存储过程中的代码。您使用DataAdapter或DataReader调用存储过程。

MySql在VB.net中执行Set和Concat语句

1 个答案: