Re: Display group title only at the first record within each group

CN <cnliou9@fastmail.fm> writes:

> Hi!
>
> Such layout is commonly seen on real world reports where duplicated
> group titles are discarded except for the first one.
>
> CREATE TABLE x(name TEXT,dt DATE,amount INTEGER);
>
> COPY x FROM stdin;
> john    2016-8-20       80
> mary    2016-8-17       20
> john    2016-7-8        30
> john    2016-8-19       40
> mary    2016-8-17       30
> john    2016-7-8        50
> \.
>
> My desired result follows:
>
> john    2016-07-08      50
>                     30
>         2016-08-19      40
>         2016-08-20      80
> mary    2016-08-17      20
>                     30

Use window functions:

SELECT CASE      WHEN lag(name) OVER (PARTITION BY name ORDER BY name, dt) IS NULL      THEN name      ELSE NULL
END,     CASE      WHEN lag(dt) OVER (PARTITION BY name, dt ORDER BY name, dt) IS NULL      THEN dt      ELSE NULL
END,     amount
 
FROM x
ORDER BY name, dt