sql distinct语句在powershel脚本中不起作用

# 加载.NET Framework中的必要程序集
Add-Type -Path "C:\path\to\System.Data.dll"

# 设置数据库连接字符串
$connectionString = "Data Source=your_server;Initial Catalog=your_database;User ID=your_username;Password=your_password"

# 创建数据库连接对象
$connection = New-Object System.Data.SqlClient.SqlConnection($connectionString)

# 打开数据库连接
$connection.Open()

# 创建SQL查询语句
$query = "SELECT DISTINCT column_name FROM table_name"

# 创建数据库命令对象
$command = New-Object System.Data.SqlClient.SqlCommand($query, $connection)

# 执行查询并获取结果
$result = $command.ExecuteReader()

# 遍历结果集并输出唯一值
while ($result.Read()) {
    $value = $result["column_name"]
    Write-Output $value
}

# 关闭结果集和数据库连接
$result.Close()
$connection.Close()