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-- 1.) Problematic way
-- This example will fail on a second execution (when first table not dropped, even in case it is executed in different connection or user context).
-- PK_SomeTable will already exist in tempdb
CREATE TABLE #SomeTable
    (
      Id INT IDENTITY(1, 1) ,
      [Name] [varchar](255) NULL ,
      CONSTRAINT [PK_SomeTable] PRIMARY KEY CLUSTERED ( [Id] ASC )
    )
-- Output:
/*
Msg 2714, Level 16, State 5, Line 3
There is already an object named 'PK_SomeTable' in the database.
Msg 1750, Level 16, State 0, Line 3
Could not create constraint. See previous errors.
*/

-- 2.) safer way 
-- Remind: always drop a temporary table when no longer needed
CREATE TABLE #SomeTable
    (
      Id INT IDENTITY(1, 1) PRIMARY KEY CLUSTERED,
      [Name] [varchar](255) NULL ,
      CONSTRAINT [PK_SomeTable] PRIMARY KEY CLUSTERED ( [Id] ASC )
    )
 /*
 Do some work
 */
 DROP TABLE #SomeTable