Create a transaction saved search to fetch the document number of invoice and IF

1. Navigate to List > Search > Saved Searches > New

2. Click Transaction

3. Search Title: Enter Title

4. Click Criteria tab

• Select Type as ‘Sales Order’

5.In the Results tab,

• Select Formula(Numeric)
• Formula: CASE WHEN {applyingtransaction.type} = ‘Invoice’   THEN {applyingtransaction.number}   ELSE NULL END
• Provide label as Invoice#

To get invoice date,

• Select Formula(Numeric)
• Formula: CASE WHEN {applyingtransaction.type} = ‘Invoice’   THEN {applyingtransaction.trandate}   ELSE NULL END
• Provide label as Invoice Date

Save the search