Who to Insert data into ODD/EVEN rows only in SQL - sql

Question

I have one table with gender as one of the columns.
In gender column only M or F are allowed.
Now i want to sort the table so that while displaying the table in gender field M and F will come alternetivly.
I have Tried....
I have tried to create one(new) table with the same structure as my existing table.
Now using high leval insert i want to insert M to odd rows and F to even rows.
After that i want to join those two statements using union operator.
I am able to insert to ( new ) the table only male or female but not to the even or odd rows...
Can any body help me regarding this....
Thanks in Advance....

Answer 1

Don't consider a table to be "sorted". The SQL server may return the rows in any order depending on execution plan, index, joins etc. If you want a strict order you need to have an ordered column, like an identity column. Usually it is better to apply the desired sorting when selecting data.
However the interleaving of M and F is a little bit tricky, you need to use the ROW_NUMBER function.
Valid SQL Server code:
CREATE TABLE #GenderTable(
[Name] [nchar](10) NOT NULL,
[Gender] [char](1) NOT NULL
)
-- Create sample data
insert into #GenderTable (Name, Gender) values
('Adam', 'M'),
('Ben', 'M'),
('Casesar', 'M'),
('Alice', 'F'),
('Beatrice', 'F'),
('Cecilia', 'F')
SELECT * FROM #GenderTable
SELECT * FROM #GenderTable
order by ROW_NUMBER() over (partition by gender order by name), Gender
DROP TABLE #GenderTable
This gives the output
Name Gender
Adam M
Ben M
Casesar M
Alice F
Beatrice F
Cecilia F
and
Name Gender
Alice F
Adam M
Beatrice F
Ben M
Cecilia F
Casesar M
If you use another DBMS the syntax may differ.

Answer 2

I think the best way to do it would be to have two queries (one for M, one for F) and then join them together. The catch would be you would have to calculate the "rank" of each query and then sort accordingly.
Something like the following should do what you need:
select * from
(select
#rownum:=#rownum+1 rank,
t.*
from people_table t,
(SELECT #rownum:=0) r
where t.gender = 'M'
union
select
#rownum:=#rownum+1 rank,
t.*
from people_table t,
(SELECT #rownum:=0) r
where t.gender = 'F') joined
order by joined.rank, joined.gender;

Answer 3

If you are using SQL Server, you can seed your two tables with an IDENTITY column as follows. Make one odd and one even and then union and sort by this column.
Note that you can only truly alternate if there are the same number of male and female records. If there are more of one than the other, you will end up with non-alternating rows at the end.
CREATE TABLE MaleTable(Id INT IDENTITY(1,2) NOT NULL, Gender CHAR(1) NOT NULL)
INSERT INTO MaleTable(Gender) SELECT 'M'
INSERT INTO MaleTable(Gender) SELECT 'M'
INSERT INTO MaleTable(Gender) SELECT 'M'
CREATE TABLE FemaleTable(Id INT IDENTITY(2,2) NOT NULL, Gender CHAR(1) NOT NULL)
INSERT INTO FemaleTable(Gender) SELECT 'F'
INSERT INTO FemaleTable(Gender) SELECT 'F'
INSERT INTO FemaleTable(Gender) SELECT 'F'
SELECT u.Id
,u.Gender
FROM (
SELECT Id, Gender
FROM FemaleTable
UNION
SELECT Id, Gender
FROM MaleTable
) u
ORDER BY u.Id ASC
See here for a working example