How to get column values in one comma separated value

In Sql Server you can use it.

DECLARE @UserMaster TABLE( 

    UserID INT NOT NULL, 

    UserName varchar(30) NOT NULL 

); 

INSERT INTO @UserMaster VALUES (1,'Rakesh')

INSERT INTO @UserMaster VALUES (2,'Ashish')

INSERT INTO @UserMaster VALUES (3,'Sagar')

SELECT * FROM @UserMaster

DECLARE @CSV VARCHAR(MAX) 

SELECT @CSV = COALESCE(@CSV + ', ', '') + UserName from @UserMaster 

SELECT @CSV AS Result

MYSQL: To get column values as one comma separated value use GROUP_CONCAT( ) function as

GROUP_CONCAT(  `column_name` )

for example

SELECT GROUP_CONCAT(  `column_name` ) 
FROM  `table_name` 
WHERE 1 
LIMIT 0 , 30

You tagged the question with both sql-server and plsql so I will provide answers for both SQL Server and Oracle.

In SQL Server you can use FOR XML PATH to concatenate multiple rows together:

select distinct t.[user],
  STUFF((SELECT distinct ', ' + t1.department
         from yourtable t1
         where t.[user] = t1.[user]
            FOR XML PATH(''), TYPE
            ).value('.', 'NVARCHAR(MAX)') 
        ,1,2,'') department
from yourtable t;

See SQL Fiddle with Demo.

In Oracle 11g+ you can use LISTAGG:

select "User",
  listagg(department, ',') within group (order by "User") as departments
from yourtable
group by "User"

See SQL Fiddle with Demo

Prior to Oracle 11g, you could use the wm_concat function:

select "User",
  wm_concat(department) departments
from yourtable
group by "User"