SQL使用列值将列名称作为公式，同时派生其他列

Question

I have a table, in which one of the column values will have the formula. What is the query to get the result.

| Student | Dept  | col1 | col2 | col3 | col4             | col5  |
|-----------------------------------------------------------------|
| 100     | ECE   | 10   | 45   | 45   | col1+col2        |  55   | 
| 101     | EEE   | 25   | 25   | 25   | col1*col2        | 625   |
| 102     | MECH  | 45   | 50   | 50   | col1/col2        |   0.9 |
| 103     | CIVIL | 35   | 30   |  3   | (Col1/Col2)*Col3 |   3.5 |
| 104     | BIO   | 45   | 90   | 90   | Col1-Col2        | -45   |
| 105     | CSE   | 60   | 16   | 65   | Col1%Col2        |  12   |

I need to write a query to derive col5 and the value should be the result of col4 for each record.

Answer 1

declare @Student int,@Dept varchar(100),@col1 int,@col2 int,@col3 int,@col4 varchar(100)
declare @stmt nvarchar(max),@params nvarchar(max),@col5 numeric(12,2)
declare @resultset table (Student int,Dept varchar(100),col1 int,col2 int,col3 int,col4 varchar(100),col5 numeric(12,2))


declare c cursor local fast_forward for select * from t

open c

while 1=1
begin

    fetch next from c into @Student ,@Dept ,@col1 ,@col2 ,@col3 ,@col4 
    if @@fetch_status != 0 break

    set @stmt = 'select @result=' +  replace(replace(replace (@col4,'Col1',@col1),'Col2',@col2),'Col3',@col3)
    set @params = N'@result numeric(12,2) out'

    exec sp_executesql @stmt,@params,@col5 out

    insert into @resultset values (@Student ,@Dept ,@col1 ,@col2 ,@col3 ,@col4 ,@col5)

end

close       c
deallocate  c

select * from @resultset

Answer 2

CREATE TABLE #CalCulation(Student INT, Dept VARCHAR(100) , col1 DECIMAL(12,2), col2 DECIMAL(12,2), col3 DECIMAL(12,2), col4 VARCHAR(100), col5  DECIMAL(12,2) ,UpFlg TINYINT DEFAULT(0))
CREATE TABLE #Calc(Id INT ,Result DECIMAL(12,2))
DECLARE @Id INT,@Col1 DECIMAL(12,2),@col2 DECIMAL(12,2), @col3 DECIMAL(12,2),@col4 VARCHAR(100),@ExecQuery VARCHAR(200)

INSERT INTO #CalCulation( Student , Dept , col1 , col2 , col3 , col4 )
SELECT 100,'ECE', 10   , 45   , 45   , 'col1+col2' UNION ALL 
SELECT 101,'EEE', 25   , 25   , 25   , 'col1*col2' UNION ALL
SELECT 102,'MECH', 45   , 50   , 50   , 'col1/col2' UNION ALL
SELECT 103,'CIVIL', 35   , 30   ,  3   , '(Col1/Col2)*Col3' UNION ALL
SELECT 104,'BIO', 45   , 90   , 90   , 'Col1-Col2' UNION ALL
SELECT 105,'CSE', 60   , 16   , 65   , 'Col1%Col2' 

WHILE EXISTS(SELECT 1 FROM #CalCulation WHERE UpFlg = 0)
BEGIN

     SELECT Top 1 @Id = Student, @col1 = col1 , @col2 = col2, @col3 = col3,@col4 = col4 FROM #CalCulation WHERE UpFlg = 0

     SET @ExecQuery = 'SELECT '+ CAST(@Id AS VARCHAR) +' ,SUM (' + REPLACE(REPLACE(REPLACE (@col4,'Col1',@col1),'Col2',@col2),'Col3',@col3) +')' 

     INSERT INTO #Calc (Id ,Result)
     EXEC (@ExecQuery) 

     UPDATE #CalCulation SET UpFlg = 1  WHERE Student = @Id
END

UPDATE #CalCulation SET col5 = Result
FROM #Calc WHERE Id = Student

SELECT * FROM #CalCulation