如何从选择查询中选择 7 行或更多行？ 即使表返回少于 7 行

Question

I want a script that gives me an exact 7 rows. For example, if my table returns only 2 rows then we have to add another 5 rows with all columns contains a null value. But if the table returns more than 7 rows then select all returned rows. Please Help!

Answer 1

Try this below logic-

Demo Here for less than 7 rows

Demo Here for more than 7 rows

WITH CTE(rn,id,name)
as
(
  select 1, null, null union all
  select 2, null, null union all
  select 3, null, null union all
  select 4, null, null union all
  select 5, null, null union all
  select 6, null, null union all
  select 7, null, null
)


SELECT a.id,a.name 
FROM
(
    select 
    ROW_NUMBER() OVER(order by id) rn,id,name
    from your_table
)A
full join CTE ON A.rn = cte.rn

Answer 2

The query is below:

with cte1 as (
  select col1,col2,...,row_number() over(order by col1) as rn,count(*) over() as cnt from table1
  union all select null,null,...,rn,cnt+1 from cte1 where rn=1 and cnt<7
)
select col1,col2,... from cte1;

dbfiddle

Answer 3

I would phrase this as:

With the FULL JOIN method, you need to list the columns you want or get seqnum in the result set:

SELECT t.*  -- or list the columns to avoid seqnum
FROM (SELECT t.*, ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) as seqnum
      FROM t
     ) t FULL JOIN
     (VALUES (1), (2), (3), (4), (5), (6), (7)) v(n)
     ON seqnum = v.n;

An alternative that does not require listing all the columns is:

select t.*
from t
union all
select t.*
from (values (1), (2), (3), (4), (5), (6), (7)) v(n) left join
     t
     on 1 = 0   -- never true
where v.n <= 7 - (select count(*) from t)

Answer 4

Create a dummy table with 2 Fields

CREATE TABLE dummy (
  id INT NOT NULL,
  NullVals VARCHAR(5) DEFAULT NULL,
  PRIMARY KEY (id));

Now insert these values to this table:

INSERT INTO dummy (id, NullVals) VALUES 
  (1, NULL),
  (2, NULL),
  (3, NULL),
  (4, NULL),
  (5, NULL),
  (6, NULL),
  (7, NULL);

run your query as follows:

Select acolumn from abc_table where acolumn like 'something'

union All

select NullVals from dummy
where id <= 7-(select count(*) from abc_table where acolumn like 'something');

Also you can replace the dummy table with CTE