Substitute the Lag() function with another similiar option in Sybase - sql

Question

With the help of some of the users here in stackoverflow, I reached to the following query. The problem is that this query works well in SQL Server, but not in Sybase as it doesn't support LAG(). I have been trying to get it to work but no success.
The query is quite complicated but help in subsituting the LAG() function with something similar would be appreciated.
SELECT created
, bname
, total_share
FROM (
SELECT TT.created
, TT.bname
, TT.total_share
, lag(TT.total_share) OVER (
PARTITION BY TT.bname ORDER BY TT.created
) AS prev_share
FROM (
SELECT DISTINCT t.created AS created
, t.NAME AS bname
, t.total_share
FROM (
SELECT cast(fsp.created AS VARCHAR(19)) AS created
, e.NAME
, e.initials
, fsp.modified
, CASE
WHEN cl.price_per_item = 0
THEN CAST('' AS DECIMAL(18, 2))
ELSE CAST((fsp.new_price / cl.price_per_item * 100) AS DECIMAL(18, 2))
END AS new_share
, CASE
WHEN cl.price_per_item = 0
THEN CAST('' AS DECIMAL(18, 2))
ELSE CAST((prev / cl.price_per_item * 100) AS DECIMAL(18, 2))
END AS old_share
, fs.STATE
, CASE
WHEN fsp.prev_price IS NULL
THEN 0
ELSE fsp.prev_price
END AS prev
, fsp.new_price AS nprice
, (prev - nprice) AS diff
, new_share - old_share AS diff_share
, old_share + diff_share AS total_share
FROM project_manager pm
INNER JOIN dba.project p ON pm.project = p.id
LEFT JOIN dba.contract c ON p.id = c.project
LEFT JOIN dba.contract_line cl ON cl.contract = c.id
LEFT JOIN dba.product pt ON cl.product = pt.id
LEFT JOIN dba.specified_product sp ON sp.product = pt.id
LEFT JOIN dba.frozen_sale fs ON fs.spec_product = sp.id
AND fs.contract = c.id
AND fs.line = cl.idx
LEFT JOIN dba.frozen_sale_split fsp ON fsp.frozen_sale = fs.id
AND fsp.employee = pm.consultant
LEFT JOIN dba.employee e ON fsp.employee = e.person
LEFT JOIN dba.person ps ON fsp.creator = ps.id
WHERE p.id = 50000002735
AND e.NAME IS NOT NULL
) AS t
) TT /* here */
) x
WHERE (
prev_share IS NULL
OR prev_share total_share
)
ORDER BY created
, bname

Answer 1

The following code is untested, but the approach is to use the row_number window function to assign a sequential number (rnum in the code) to each row, ordered by the created value. This is done in the initial CTE. The main query then joins that CTE to itself, with a join condition of a difference of one in the rnum values.
with inp as (
SELECT TT.created
, TT.bname
, TT.total_share
, row_number over(order by TT.created) as rnum
FROM (
SELECT DISTINCT t.created AS created
, t.NAME AS bname
, t.total_share
FROM (
SELECT cast(fsp.created AS VARCHAR(19)) AS created
, e.NAME
, e.initials
, fsp.modified
, CASE
WHEN cl.price_per_item = 0
THEN CAST('' AS DECIMAL(18, 2))
ELSE CAST((fsp.new_price / cl.price_per_item * 100) AS DECIMAL(18, 2))
END AS new_share
, CASE
WHEN cl.price_per_item = 0
THEN CAST('' AS DECIMAL(18, 2))
ELSE CAST((prev / cl.price_per_item * 100) AS DECIMAL(18, 2))
END AS old_share
, fs.STATE
, CASE
WHEN fsp.prev_price IS NULL
THEN 0
ELSE fsp.prev_price
END AS prev
, fsp.new_price AS nprice
, (prev - nprice) AS diff
, new_share - old_share AS diff_share
, old_share + diff_share AS total_share
FROM project_manager pm
INNER JOIN dba.project p ON pm.project = p.id
LEFT JOIN dba.contract c ON p.id = c.project
LEFT JOIN dba.contract_line cl ON cl.contract = c.id
LEFT JOIN dba.product pt ON cl.product = pt.id
LEFT JOIN dba.specified_product sp ON sp.product = pt.id
LEFT JOIN dba.frozen_sale fs ON fs.spec_product = sp.id
AND fs.contract = c.id
AND fs.line = cl.idx
LEFT JOIN dba.frozen_sale_split fsp ON fsp.frozen_sale = fs.id
AND fsp.employee = pm.consultant
LEFT JOIN dba.employee e ON fsp.employee = e.person
LEFT JOIN dba.person ps ON fsp.creator = ps.id
WHERE p.id = 50000002735
AND e.NAME IS NOT NULL
) AS t
) TT
)
SELECT
created
, bname
, total_share
, prev.total_share as prev_share
FROM
inp
left join inp as prev on prev.rnum=inp.rnum-1
and prev.bname=inp.bname
WHERE (
prev.total_share IS NULL
OR prev.total_share total_share
)
ORDER BY
created
, bname