Removing trailing zeros in case statement - sql

Question

I've been trying to remove the trailing zeros from a column of a table. It works well when I try to remove the zeros from the column. However, when I use it with 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. For example, I've hard coded the column as a constant value; while 1=0 (false), it is retrieving the value removing the zeros. It should be true in the else statement.
SELECT CASE WHEN 1=0 THEN cast(CAST(123.45000 AS decimal(6,2)) as float)
ELSE
'123.456700'
END
SELECT CASE WHEN 1=0 THEN CONVERT(DOUBLE PRECISION, 123.456700)
ELSE
'123.456700'
END
Why is this happening? Can anyone help me with this?
The above is well explained by #Tim below.
However, it doesn't remove the zeros at all in a table. It doesn't recognize the flag at all. Here is an example:
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)
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

Answer 1

As #JNevill commented, what is happening here is that an implicit conversion is happening in the ELSE branch of your CASE expression, converting the string literal into a float, thereby removing the trailing zeroes when it gets printed. One option would be to cast the IF portion to VARCHAR:
SELECT
CASE WHEN 1=0
THEN CAST(CAST(123.45000 AS decimal(6,2)) AS varchar(max)) -- a string
ELSE '123.456700' END -- also a string
Demo
Note that in certain versions of SQL (other than yours) your CASE expression would not even run without error. It just so happens that a silent conversion is taking place here.

Answer 2

You can't remove trailing zeroes from a decimal data type. The decimal/numeric data types are fixed point data type:
Numeric data types that have fixed precision and scale. Decimal and numeric are synonyms and can be used interchangeably.
This means that the decimal point is in a fixed position within the stored number, unlike float and read which are floating point data types - so for a decimal(9,2) there will always be two digits to the right of the decimal point - and for numeric(5,3) where will always be three digits to the left of the decimal point.
If precision is not very important, you can convert to float - but you should be aware that unlike decimal, float is an approximate data type.
Please note that you would still have to convert both branches of the case statement to a varhcar otherwise SQL Server will implicitly convert both branches to float and it will look like the flag is being ignored.
DECLARE #flag INT = 1
SELECT
CASE WHEN #flag = 1
THEN CAST(CAST(amount AS float) as varchar(30))
ELSE CAST(amount as varchar(30))
END As [Remove trailing zeros],
-- This is to show the opposite branch
CASE WHEN #flag = 0
THEN CAST(CAST(amount AS float) as varchar(30))
ELSE CAST(amount as varchar(30))
END As [Include trailing zeros]
FROM #tablea
Results:
Remove trailing zeros Include trailing zeros
1.1 1.10
1 1.00
0.9 0.90
0.09 0.09

Answer 3

#Tim, thanks. It works in the demo you showed. But it doesn't remove the zeros at all in a table. It doesn't recognize the flag at all. Here is an example:
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)
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