Comparing 2 items at different dates
I don't have access to a Netezza device, but according to the wiki, 


  Netezza software was based on PostgreSQL 7.2,[9] but did not maintain
  compatibility.


so, I'll use the PostgreSQL option for the fiddle which you can find here. According to the documentation, Netezza has Window/Analytic functions.

What I did to answer your question was:

Create a share table:

CREATE TABLE share 
(
  t_date  DATE NOT NULL, -- BAD IDEA to use SQL keywords for fieldnames! 
  account INTEGER NOT NULL,
  price   INTEGER NOT NULL
);


Populate it:

INSERT INTO share 
VALUES
('2020-02-01',       100,                    200),
('2020-02-01',       101,                    200),
('2020-02-01',       102,                    200),
('2020-02-02',       100,                    210),
('2020-02-02',       101,                    200),
('2020-02-02',       102,                    200);


Then I ran the following query (using Window - or Analytic - functions):

SELECT
  ROW_NUMBER() OVER() as rn,
  t_date AS d, account AS a, 
  LAG(price) OVER () AS la, price, LEAD(price) OVER() AS le
FROM share;


Result:

rn  d   a   la  price   le
1   2020-02-01  100     200 200
2   2020-02-01  101 200 200 200
3   2020-02-01  102 200 200 210
4   2020-02-02  100 200 210 200
5   2020-02-02  101 210 200 200
6   2020-02-02  102 200 200 


The rn field is a proxy PRIMARY KEY - I presume your table has one? OK, so far so good. But, you can't put Window functions in a where clause, so this will be our basis for the following query:

SELECT 
  rn, d AS tx_date, a AS acct, la AS previous, price, le AS future,
  CASE
    WHEN le &gt; la THEN 'Increase'
    ELSE 'Decrease'
  END AS action
FROM
(
  SELECT
    ROW_NUMBER() OVER() as rn,
    t_date AS d, account AS a, 
    LAG(price) OVER () AS la, price, LEAD(price) OVER() AS le
  FROM share
) AS tab
WHERE le != la;


Result:

rn  tx_date     acct    previous    price   future  action
3   2020-02-01  102          200      200      210  Increase
5   2020-02-02  101          210      200      200  Decrease


So, this is, I think, pretty much what you wanted. Following tranaction 3, there was an increase and prior to transaction 5 there was a decrease. If you want the focus to be on transaction 4, then just play around with the SQL - it shouldn't be too difficult. Window/Analytic functions are very powerful and well worth learning! BTW, next time you ask a question, could you please provide your table structures as DDL (CREATE TABLE foo...) and your data as DML (INSERT INTO foo VALUES (...) - or use a fiddle. p.s. welcome to the forum!