How do I update data in a table based on conditions from another table?

 You can update data in one table using values from another table by using a join in the UPDATE statement:

UPDATE t1

SET t1.ColumnToUpdate = t2.NewValue

FROM YourTable1 t1

INNER JOIN YourTable2 t2

    ON t1.ID = t2.ID

WHERE t2.ConditionColumn = 'SomeValue';

This updates ColumnToUpdate in YourTable1 with values from NewValue in YourTable2 where a condition is met.