cross and left to find missing, Sql Server

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create table categories (
   ArticleID   INTEGER  NOT NULL  
  ,ThemeID     INTEGER  NOT NULL
  ,ThemeName   VARCHAR(7) NOT NULL
  ,Code  BIT  NOT NULL
  ,CreatedTime VARCHAR(7) NOT NULL,
  primary key (ArticleID, ThemeID)
);

INSERT INTO categories (ArticleID, ThemeID,ThemeName,Code,CreatedTime) VALUES 
(1,1,'tob',1,'57:30.7'),
 (1,2,'ecig',1,'03:58.3'),
(1,5,'rnorm',0,'42:56.5'),
 (2,1,'tob',1,'57:30.7'),
 (2,2,'ecig',0,'03:58.3'),
(2,5,'rnorm',1,'42:56.5'),
(2,6,'raddict',0,'42:59.8'),
 (3,1,'tob',1,'57:30.7'),
 (3,2,'ecig',0,'03:58.3'),
 (3,5,'rnorm',0,'42:56.5'),
 (21,1,'tob',1,'57:30.7'),
 (21,2,'ecig',0,'03:58.3'),
 (21,5,'rnorm',0,'42:56.5'),
 (21,6,'raddict',0,'42:59.8');

create table #mycategories (
  CatID INT  NOT NULL PRIMARY KEY, 
  CatName VARCHAR(7) NOT NULL,
  CreatedTime DATETIME  NOT NULL DEFAULT GETDATE()
);

insert into #mycategories (CatID, CatName) values 
(1,'tob'),
(2,'ecig'),
(5,'rnorm'),
(6,'raddict');

create table #myarticles (
   ArticleID INT  NOT NULL PRIMARY KEY,
   CreatedTime DATETIME  NOT NULL DEFAULT GETDATE()
);

INSERT INTO #myarticles (ArticleID)
select ArticleID 
from categories
group by ArticleID;

select a.ArticleID, c.CatName
from #myarticles a
cross join #mycategories c
left join categories ca on (ca.ArticleID = a.ArticleID and ca.ThemeID = c.CatID)
where ca.ArticleID is null;

View schema
Execution time: 0,03 sec, rows selected: 2, rows affected: 22, absolute service time: 0,22 sec, absolute service time: 0,21 sec