Question

need help/guide for sql select query, I have 2 table stock and stock_history, in stock will have initial values for stock
and before update the stock table,stock_history will be inserted 1st from stock table, my case is need to get status of stock based on selection date,
this is to track open stock balance and close stock balance, close stock balance is easy where just need to fetch data from table stock
for particular timestamp, but the critical part is when to fetch data for open stock balance where need trace the status for specific timestamp,
this only can be done by refering the history table, so i need the sql where need to select data from both stock and stock_history

status table
id  desc
--  ----
01  consignment
02  customer
03  bank
04  safekeep
05  exit

stock
-----
ref_no   serial_no      status  timeStamp
1        001            04        2012-03-01 09:03:00

stock_history
-------------
ref_no   serial_no  status  timeStamp
1        001        01      2012-03-01 09:00:00
1        001        03      2012-03-01 09:01:00
1        001        02      2012-03-01 09:02:00

 so, when choose for date 
 01/03/12 time 9:01   =   1    001  03  2012-03-01 09:01:00
 01/03/12 time 9:01   =   1    001  03  2012-03-01 09:01:00

please help, thanks in advance

Answer 1

You can use the UNION operator to select from multiple tables:

SELECT * FROM stock
UNION ALL
SELECT * FROM stock_history
WHERE ...

That said, I’d suggest restructuring your schema. Why have a separate “stock” and “stock_history” table? You really only need one “stock” table to store both — the “current” stock is just the one with the highest status. Or you could even be explicit and maintain an “is_current” flag row.

Update: Changed UNION to UNION ALL. The ALL means just combine the rows for both tables, no extra processing. Leaving it off will attempt to remove any duplicate rows first, which could be less efficient (and makes no difference in the results here since duplicates are not possible with your schema). Hat tip to @SmartestVEGA.