Incorrect syntax near the keyword 'IN' - sql

Question

Getting error near IN and here is my code

 DECLARE @DateFrom DateTime ='2018-04-01',
            @DateTo DateTime = '2018-05-31'

            WHILE @DateTo < @DateFrom 
            BEGIN
            set @DateFrom = DATEADD(D,1,@DateFrom)
             SET @DateFrom = DATENAME(DW, @DateFrom) IN ( 'tuesday','friday',null)
            END

I am getting error like

Incorrect syntax near the keyword 'IN'.

Answer 1

If this is really mysql there are lots of errors 1) You don't declare @ variables 2) To allocate a value to a variable use a set statement or if it's a declared variable you can default a value 3) While statements syntax is incorrect it should be while something DO ... END WHILE 4) Every statement must be terminated 5) Multi code procedures must enclosed in a BEGIN..END block 5) This code must be in a stored program (procedure,trigger,function) 6) Delimiters possibly not set.

This at least syntaxs But I don't get what you are trying to do with the in statement.

drop procedure if exists p;

delimiter $$
create procedure p()
begin
set @DateFrom ='2018-04-01',
    @DateTo   = '2018-05-31';

   WHILE @DateTo < @DateFrom do 
      set @DateFrom = DATEADD(D,1,@DateFrom);
      SET @DateFrom = DATENAME(DW, @DateFrom) IN ( 'tuesday','friday',null);

   END while;
end $$
delimiter ;

Answer 2

DECLARE @DateFrom DateTime ='2018-04-01',
@DateTo DateTime = '2018-05-31'

WHILE @DateTo < @DateFrom 
BEGIN
set @DateFrom = DATEADD(D,1,@DateFrom)
    SET @DateFrom = case when DATENAME(DW, @DateFrom) IN ( 'tuesday','friday',null) then @DateFrom else null end

END