删除尾随零以及case语句

Question

I've been trying to remove the trailing zeros from a column of a table. When I use a case statement (to remove the zeros when a flag is turned on, and to keep them when a flag is turned off) it doesn't work properly. It doesn't recognize the flag. @Tim Biegeleisen has helped me explain the implicit conversion that was happening though.

I want to remove or retain the zeros interchangeably. When the flag is on for example, I would like 0.091000 be 0.091; and when the flag is off, I want it be the same 0.091000. For example, this works properly to retrieve removing the zeros and retaining the zeros separately.

CREATE TABLE #tablea 
(item CHAR(2), name VARCHAR(10), amount DECIMAL(9,2)) 

INSERT INTO #tablea 
VALUES ('AB', 'D1', 1.10), 
       ('AB', 'D2', 1.00), 
       ('AB', 'D3', 0.90), 
       ('AB', 'D4', 0.09)    

SELECT  CAST(CAST(amount AS DECIMAL(6,2)) AS VARCHAR(max)), cast(CAST(amount 
AS decimal(6,2)) as float)  
FROM #tablea 

It displays two columns: one with the zeros and one without the zeros.

However, it doesn't remove the zeros at all in a table. It doesn't recognize the flag at all. Here is an example:

DECLARE @flag INT = 1

SELECT CASE WHEN @flag = 1 
THEN CAST(CAST(amount AS DECIMAL(6,2)) AS VARCHAR(max))
ELSE amount END 
FROM #tablea 

Can anyone help me with this?

Answer 1

A CASE expression will always return a value of the same data type, according to the data type precedence rules . In your case, considering a branch is returning a varchar and the other one is returning a decimal , the result will always be a decimal .

To get the desired results, change the CASE expression to return the same data type in both branches:

DECLARE @flag INT = 1

SELECT CASE WHEN @flag = 1 
THEN CAST(CAST(amount AS DECIMAL(6,2)) AS VARCHAR(100))
ELSE CAST(CAST(amount AS FLOAT) AS VARCHAR(100)) END 
FROM #tablea 

Answer 2

You can do this in this way...

    CREATE TABLE #tablea (item CHAR(2), name VARCHAR(10), amount decimal(18,6), flag int) 

    INSERT INTO #tablea 
    VALUES ('AB', 'D1', 1.10, 1), 
           ('AB', 'D2', 1.00, 0), 
           ('AB', 'D3', 0.90, 1), 
           ('AB', 'D4', 0.09, 0)    

    SELECT case when  flag = 1 then FORMAT(amount, 'n2') else FORMAT(amount, 'n4')  end amt FROM #tablea