SharePoint Validations

RJF61 You can add validation in SharePoint lists at two places:

1. Column validation: You can add validation to specific column from column settings. This cannot reference other columns in list in validation formula
2. List validation: You can add validation to list item based on any supported column values from List settings  > Validation settings. You can reference multiple columns in this validation formula and use nested IF expressions as per your requirements.

Documentation: Introduction to SharePoint formulas and functions 

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