Combining two rows in one select query - sql

Question

Hi I am having a hard time combining two records (from a single table) on a single query. The idea is, DATE_FIELD column is a date type and ColA is an integer data type.
To further illustrate my inquiry, I have attached an image below
1.) Is the raw table.
2.) Is the desired output.
P.S. The filter for DATE_FIELD is not a simple "WHERE DATE_FIELD IN" clause.
For example, I wanted to get the DATE_FIELD=12/30/2013. Then I need to get the Previous Sept DATE_FIELD also, which is 9/30/2013 programatically by using this query that I got from the web:
CASE
WHEN MONTH(DATE_FIELD) < 10
THEN
(cast(CAST((DATE_FIELD) - 1) as char(4)) + RIGHT('00' + LTRIM(09),2) + RIGHT('00' + LTRIM(30),2) AS Date))
ELSE
( cast(CAST((YEAR(DATE_FIELD)) as char(4)) + RIGHT('00' + LTRIM(09),2) + RIGHT('00' + LTRIM(30),2) AS Date))
END
Here is my current sql script (which cannot get the ColA equivalent for Previous Sept filter:
SELECT DATE_FIELD, ColA,
CASE
WHEN MONTH(DATE_FIELD) < 10
THEN
(cast(CAST((YEAR(DATE_FIELD) - 1) as char(4)) + RIGHT('00' + LTRIM(09),2) + RIGHT('00' + LTRIM(30),2) AS Date))
ELSE
( cast(CAST((YEAR(DATE_FIELD)) as char(4)) + RIGHT('00' + LTRIM(09),2) + RIGHT('00' + LTRIM(30),2) AS Date))
END AS PREVIOUS,
(
SELECT ColA
FROM TABLE_A
WHERE DATE_FIELD =
CASE
WHEN MONTH(DATE_FIELD) < 10
THEN
(cast(CAST((YEAR(DATE_FIELD) - 1) as char(4)) + RIGHT('00' + LTRIM(09),2) + RIGHT('00' + LTRIM(30),2) AS Date))
ELSE
( cast(CAST((YEAR(DATE_FIELD)) as char(4)) + RIGHT('00' + LTRIM(09),2) + RIGHT('00' + LTRIM(30),2) AS Date))
END
) AS PYE_colA
FROM TABLE_A
WHERE DATE_FIELD = '12/30/2013'
Thanks!

Answer 1

Do a cross join with the same table and use your CASE structure only in the where clause:
SELECT a.DATE_FIELD AS DATE_FIELD_1,
a.ColA AS ColA_1,
b.DATE_FIELD AS DATE_FIELD_2,
b.ColA AS ColA_2
FROM TABLE_A a
CROSS JOIN TABLE_A b
WHERE DATE_FIELD_1 = 'your date'
AND DATE_FIELD_2 = (
CASE
WHEN MONTH(DATE_FIELD_1) < 10
THEN
(cast(CAST((YEAR(DATE_FIELD_1) - 1) as char(4)) + RIGHT('00' + LTRIM(09),2) + RIGHT('00' + LTRIM(30),2) AS Date))
ELSE
( cast(CAST((YEAR(DATE_FIELD_1)) as char(4)) + RIGHT('00' + LTRIM(09),2) + RIGHT('00' + LTRIM(30),2) AS Date))
END)
;
Another possibility based on Thorsten Kettners remarks:
SELECT a.DATE_FIELD AS DATE_FIELD_1,
a.ColA AS ColA_1,
b.DATE_FIELD AS DATE_FIELD_2,
b.ColA AS ColA_2
FROM TABLE_A a
INNER JOIN TABLE_A b
ON b.DATE_FIELD = (
CASE
WHEN MONTH(a.DATE_FIELD) < 10
THEN
(cast(CAST((YEAR(a.DATE_FIELD) - 1) as char(4)) + RIGHT('00' + LTRIM(09),2) + RIGHT('00' + LTRIM(30),2) AS Date))
ELSE
( cast(CAST((YEAR(a.DATE_FIELD)) as char(4)) + RIGHT('00' + LTRIM(09),2) + RIGHT('00' + LTRIM(30),2) AS Date))
END)
WHERE a.DATE_FIELD = 'your date'
;