Explain the COLUMNS_UPDATED function and its relation to Sparse Column

The COLUMNS_UPDATED function returns a varbinary value to indicate all the columns that were updated during a DML action. The bits that are returned by the COLUMNS_UPDATED function are as follows:

• When a sparse column is explicitly updated, the corresponding bit for that sparse column is set to 1, and the bit for the column set is set to 1.
• When a column set is explicitly updated, the bit for the column set is set to 1, and the bits for all the sparse columns in that table are set to 1.
• For insert operations, all bits are set to 1.