CHAR Datatype and ConCat in Oracle and SQL Server.

Char is a Fixed length data type, provided by database to stored Character Data.
It will allocate fix bytes as per length specified for CHAR datatype and will pad with Space for remaining chunks.

With Variable declare as CHAR(20), Byte allocated will be always 20.

DECLARE @Var CHAR(20)='Hello'
SELECT DATALENGTH(@Var) as DataLen
GO

Output :
DataLen
20


Now lets see how it behave in case of CONCAT for Oracle and SQL Server.

SQL Server:
We are declaring a CHAR Datatype with Length(20), and trying to ConCat.

DECLARE @Var CHAR(20)='Hello-'
SET @Var= @Var+'SQL Server'
SELECT @Var
GO

OUTPUT: "Hello- "

In Case of SQL Server, even after Concat it only displaying previous assign Data due to initial padded space.
With we Declare CHAR(20) and assign it “Hello-“, it is actualy Stored as

“Hello-00000000000000”

0 represent Space and total DataLength is 20.

So any Concat is Beyond length specified for @Var i.e. 20, Hence Concat is not possible.
But it wont throw any Exception or Error, it will whitewash any ConCat.

Oracle:

SET serveroutput ON;
DECLARE
var_1 CHAR(20000) := 'HELLO-';
BEGIN
var_1 := var_1 || 'ORACLE';
dbms_output.put_line(var_1);
END;

Output:
ORA-06502: PL/SQL: numeric or value error: character string buffer too small
ORA-06512: at line 4
06502. 00000 - "PL/SQL: numeric or value error%s"

Oracle will Throw exception for such Concat with CHAR Datatype.
Unless we Use TRIM, Oracle will throw exception for any Concat with CHAR Datatype.