What does coalesce do ?

Answer 1

The COALESCE function in SQL returns the first non-NULL expression among its arguments.
Syntax
COALESCE ("expression 1", "expressions 2", ...)

Example
DECLARE @Name 1 varchar(20)
DECLARE @Name 2 varchar(20)

SET @Name2 = 'Jack'

SELECT COALESCE(@Name1, @Name2) As 'Chosen Name'

-- Results
=========================
Chosen Name
-----------
Jack

Answer 2

can you explain thé syntax please ? @Akwin

Answer 3

Coalesce returns the first non null value.
Syntax
COALESCE( expression1, expression2, ... expression_n )

Example
SELECT COALESCE(NULL, NULL, 'Akwin', NULL, 'Lopez');
result : Akwin

the above example returns the first non null value
Return Types
Returns the data type of expression with the highest data type precedence. If all expressions are nonnullable, the result is typed as nonnullable.

Remarks
If all arguments are NULL, COALESCE returns NULL. At least one of the null values must be a typed NULL.

@Dhana Sekar , Hope I have cleared your doubt