我正在尝试从 MySQL 获取一些值 - 列作为行,反之亦然 - 以显示在DataGridView
. 我有这段代码,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
将所有这些代码保存在一个字符串中来通过命令运行它时,我得到一个MySQLException
错误-Fatal error encountered during command execution.
我试图将代码拆分为单独的字符串,但弹出相同的错误。也试图增加CommandTimeout
,但没有任何效果。
有什么特殊的方法可以运行这些语句吗?还是代码有问题?请注意,这在命令行客户端上有效运行,没有任何错误。
PS:代码来自 Q# 3288014 - 感谢 Anax
编辑:
我找到了解决同一件事的方法,但都是在 VB 中完成的。
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
有趣的是,在 MySQL 中所有可以在字符串中完成的事情,在 VB 中需要这么多代码。