COALESCE is a function in SQL that returns the first non-null value in a list of arguments. It evaluates the arguments in order and returns the first non-null value from the argument list. If all the values in the list are NULL, then the function returns NULL. The SQL Coalesce function is used to handle NULL values and replace them with user-defined values during the expression evaluation process. The function can have multiple expressions in it, and the data types of the expressions must be the same. The SQL Coalesce function is a syntactic shortcut for the CASE expression in SQL. It is used to select the columns and replace NULL values with a default value. The COALESCE function can be used in a function to make it more general, and by putting it in a computed column, you can improve its accuracy.