Oracle SQL LAG Function - sql

Question

I'd appreciate some help with this code, I'm getting a 'missing keyword' error. I've never used the Lag function before, so hopefully I using it correctly. Thanks for your help. Gav
CREATE VIEW GS_Date AS
SELECT
DATE_DATE,
DATE_FLAG,
CASE WHEN LAG ( DATE_FLAG) OVER ( ORDER BY DATE_DATE ) = '1' THEN DATE_STEP = ( LAG ( DATE_FLAG) OVER ( ORDER BY DATE_DATE ) ) + '1'
WHEN LAG ( DATE_FLAG) OVER ( ORDER BY DATE_DATE ) = '0' AND LAG ( DATE_FLAG) OVER ( ORDER BY DATE_DATE ) = '-1' THEN DATE_STEP = ( LAG ( DATE_FLAG) OVER ( ORDER BY DATE_DATE ) ) + '1'
ELSE DATE_STEP = LAG ( DATE_FLAG) OVER ( ORDER BY DATE_DATE ) END AS DATE_STEP
FROM DATE_GROUP

Answer 1

The problem is with the CASE expression; you were using LAG correctly.
Other points: Don't add strings like '1' and '-1' to numbers. Add numbers - you don't need the single quotes.
Also, if in a computation something is common and only the "last part" is different, you can use the CASE expression "at the end". Like below:
Note: On re-reading the original post, the formula needs to be more complicated (I didn't get it exactly right). Not changing the answer, since it still illustrates the same ideas I meant to share. BUT: Looking at the original post, there is a condition "when LAG = 0 and LAG = -1" - that can never be true. What was meant is probably "OR" instead of "AND". In the formula I wrote below, this means one more WHEN...THEN... branch.
LAG(DATE_FLAG) OVER (ORDER BY DATE)
+ CASE LAG(DATE_FLAG) OVER (ORDER BY DATE ) WHEN 1 THEN 1
WHEN 0 THEN -1
ELSE 0 END AS DATE_STEP
Further edit: Looking at it again, it seems when the flag is 1, 0 or -1 then we must add 1, otherwise add 0... then it's easier to use a "simple CASE expression" instead of a "searched CASE expression" as I did. Something like:
LAG(...) ...
+ CASE WHEN LAG(...) ... IN (-1, 0, 1) THEN 1
ELSE 0 END AS DATE_STEP

Answer 2

Try like this
CREATE VIEW GS_Date AS
SELECT DATE_DATE,
DATE_FLAG,
CASE
WHEN LAG(DATE_FLAG) OVER(ORDER BY DATE_DATE) = '1' THEN
(LAG(DATE_FLAG) OVER(ORDER BY DATE_DATE)) + '1'
WHEN LAG(DATE_FLAG) OVER(ORDER BY DATE_DATE) = '0' AND LAG(DATE_FLAG) OVER(ORDER BY DATE_DATE) = '-1' THEN
(LAG(DATE_FLAG) OVER(ORDER BY DATE_DATE)) + '1'
ELSE
LAG(DATE_FLAG) OVER(ORDER BY DATE_DATE)
END AS DATE_STEP
FROM DATE_GROUP

Answer 3

So you don't have to keep writing LAG( ... ) OVER ( ... ) statements, get the LAG value in a sub-query and then use CASE or DECODE in the outer query:
CREATE VIEW GS_Date AS
SELECT DATE_DATE,
DATE_FLAG,
DECODE(
DATE_STEP,
1, 2,
0, 1,
-1, 0,
DATE_STEP
) AS DATE_STEP
FROM (
SELECT DATE_DATE,
DATE_FLAG,
LAG ( DATE_FLAG ) OVER ( ORDER BY DATE_DATE ) AS DATE_STEP
FROM DATE_GROUP
)'
Also, your second WHEN clause will never be true:
WHEN LAG ( DATE_FLAG ) OVER ( ORDER BY DATE_DATE ) = '0'
AND LAG ( DATE_FLAG ) OVER ( ORDER BY DATE_DATE ) = '-1'
THEN ...
Since the value can never be both -1 and 0. I've assumed you meant to use OR rather than AND.