使用PowerShell导出含GUID的SQL数据集至CSV时，如何将唯一标识符转为大写

When exporting a SQL dataset where the first column contains unique identifiers (GUIDs), PowerShell/.NET automatically converts GUIDs to lowercase. Since the downstream system requires GUIDs to be in uppercase, what's the cleanest way to achieve this? The current export code is:
$DataSet.Tables[0] | Export-Csv $OuputFile -NoTypeInformation

Cleanest Ways to Fix This #

1. Transform the GUID Column Directly (Most Straightforward) #

The simplest and most readable approach is to tweak the GUID values as part of your pipeline before exporting. Use Select-Object to target either the known column name or the first column dynamically, converting each GUID to uppercase:

# If you know the exact column name (swap 'GuidColumn' with your actual column name)
$DataSet.Tables[0] | 
  Select-Object @{Name='GuidColumn'; Expression={$_.GuidColumn.ToString().ToUpper()}}, * -ExcludeProperty GuidColumn |
  Export-Csv $OutputFile -NoTypeInformation

# If you need to target the first column dynamically (no hardcoded name)
$firstCol = $DataSet.Tables[0].Columns[0].ColumnName
$DataSet.Tables[0] | 
  Select-Object @{Name=$firstCol; Expression={$_.$firstCol.ToString().ToUpper()}}, * -ExcludeProperty $firstCol |
  Export-Csv $OutputFile -NoTypeInformation

2. Reusable Type Converter (For Multiple Scripts/Datasets) #

If you're dealing with this requirement across multiple datasets or scripts, a custom type converter will make this behavior automatic without repeating code each time:

# Add a custom type converter for GUIDs that outputs uppercase
Add-Type @"
using System;
using System.ComponentModel;
public class UppercaseGuidConverter : TypeConverter {
    public override object ConvertTo(ITypeDescriptorContext context, System.Globalization.CultureInfo culture, object value, Type destinationType) {
        if (value is Guid guid && destinationType == typeof(string)) {
            return guid.ToString("D").ToUpper();
        }
        return base.ConvertTo(context, culture, value, destinationType);
    }
}
"@

# Attach the converter to your first (GUID) column
$DataSet.Tables[0].Columns[0].ExtendedProperties["TypeConverter"] = [UppercaseGuidConverter]::new()

# Now export like normal—GUIDs will be uppercase automatically
$DataSet.Tables[0] | Export-Csv $OutputFile -NoTypeInformation

3. Post-Process the CSV (Quick One-Liner Hack) #

If you don't want to modify the dataset itself, export normally then do a find-and-replace on the CSV file. Just note this works best if your CSV doesn't have other lowercase strings that match GUID formatting:

# Export as usual first
$DataSet.Tables[0] | Export-Csv $OutputFile -NoTypeInformation

# Replace all lowercase GUIDs with uppercase versions
(Get-Content $OutputFile) -replace '\b[a-f0-9]{8}-[a-f0-9]{4}-[a-f0-9]{4}-[a-f0-9]{4}-[a-f0-9]{12}\b', { $_.Value.ToUpper() } | Set-Content $OutputFile

My Recommendation #

Stick with the first method for one-off tasks—it's efficient, easy to read, and avoids extra steps like file I/O or custom type setup. If you need this behavior consistently across multiple projects, the type converter approach will save you time in the long run.

内容的提问来源于stack exchange，提问作者Alec Thomas