Question

嗨，大家好我正在尝试编写一些代码来检查MySQL数据库是否存在，然后在控制台中写一行（如果存在或不存在）。

我做了一些谷歌搜索并发现了这段代码，但是我得到了一个语法错误，如果有人知道如何做到这一点，将不胜感激。

Function DoesDBExist(DBConnectionString As String, Logger As String)

    Dim exists As Byte = 0

    Dim conn As MySqlConnection = New MySqlConnection(DBConnectionString)

    Dim cmd As MySqlCommand = New MySqlCommand("SELECT case when exists " & _
       "(select 1 from sys.Databases SELECT case when exists " & _
       "(select 1 from sys.Databases where Name = @DbName) " & _
       "then 1 else 0 end as DbExists", conn)

    cmd.Parameters.AddWithValue("@DbName", "MDLUpdate")

    conn.Open()

    exists = CByte(cmd.ExecuteScalar())
    Console.WriteLine(exists)
    Console.ReadKey()
    conn.Close()

    Return CBool(exists)

End Function

请原谅我的标签，我不能100％确定使用哪些标签

Answer 1

您的代码可能是这样的

Function DoesDBExist(DBConnectionString As String, Logger As String) as Boolean

    Dim conn As MySqlConnection = New MySqlConnection(DBConnectionString)
    Dim cmd As MySqlCommand = new MySqlCommand("SELECT IF(EXISTS (SELECT SCHEMA_NAME " & _
        "FROM INFORMATION_SCHEMA.SCHEMATA WHERE SCHEMA_NAME = @DbName), 'Y','N')", conn) 
    cmd.Parameters.AddWithValue("@DbName", "MDLUpdate")
    conn.Open()
    Dim exists As String = cmd.ExecuteScalar().ToString()
    Console.WriteLine(exists)
    conn.Close()
    Return IF(exists = "Y", True, False)

End Function

检查MySQL数据库是否存在VB

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