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using a SELECT statement in a  THEN  of a CASE statement.

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Last Modified: 2017-04-24
I am trying to make a conversion script that takes a measurement and converts it to a different unit.
Example centimeter to milometers.   I don’t want to make the field case sensitive in case someone would put  Inch or inch in @p2 I want it to return the same value but certain  values need to be case sensitive ‘mm’ could be Mega meters  or Millimeters. Therefore I was trying to use  a select statement in the then section of the where clause an it is giving me Incorrect syntax near the keyword 'select'.
Below is the code

declare  @P1 VARCHAR(max) –- value of the measurement
declare @P2 VARCHAR(max) –- original unit
declare  @P3 VARCHAR(max)—new unit
DECLARE @pos INT;
DECLARE @cleanInput VARCHAR(100);

set @P1 = '12'
set @P2 = 'm'
set @P3 = 'inch'

 SET @cleanInput ='';
      SET @pos = 1;

      WHILE @pos <= Len(@P1)
        BEGIN
            SET @cleanInput= @cleanInput + CASE WHEN Isnumeric(Substring(@P1,
                             @pos
                             , 1)
                             )
                             = 1 THEN Substring(
                             @p1, @pos, 1) ELSE '' END;
            SET @pos = @pos + 1;
        END;

      --SET @cleanInput = Replace(@CleanInput, ',', '');
      SET @cleanInput = Replace(@CleanInput, '$', '');


 set @cleanInput =  case
                                     when @P2 = 'mm' then select (  cast (@cleanInput as float) *multiplier
                                                                                                 from [L_Conversion_Table ]                                          
                                                                                                       where ASCII( type) = ASCII(@P2))
                                    Else @cleanInput
                                                                                    
                                    end
Comment
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HainKurtSr. System Analyst
CERTIFIED EXPERT

Commented:
try

declare @mm as float;
select @mm = multiplier
from [L_Conversion_Table ]                                          
where ASCII( type) = ASCII(@P2));

 if (@P2 = 'mm') set @cleanInput = cast (@cleanInput as float) *multiplier;

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SQL Server Consultant
Commented:
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Author

Commented:
(select (  cast (@cleanInput as float) *multiplier
                                                                                                 from [L_Conversion_Table ]                                          
                                                                                                       where ASCII( type) = ASCII(@P2)))

it then gives me incorrect Incorrect syntax near the keyword 'from'.
Megan BrooksSQL Server Consultant

Commented:
I don't think the syntax of your SELECT is correct. You have an open parenthesis from after the SELECT keyword that is not closed before FROM. Debug your query first, wrap it in parentheses, and then you should be able to use it as an expression in CASE.
HainKurtSr. System Analyst
CERTIFIED EXPERT

Commented:
or try
if @P2 = 'mm' 
 select @cleanInput = cast (@cleanInput as float) *multiplier
  from [L_Conversion_Table ]                                          
 where ASCII( type) = ASCII(@P2);

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