select data from last 2 rows sql

Question

Im using an odbc-jdbc bridge in my project and I need select 2 pieces of data from the database and save the data to 2 variables on the java side of my application. Here is an example of my table.

SITE_ID ------- DEV_ID ------- SCHEDULE_TIME ------- VALUE_ENUM ------- IDX
---------------------------------------------------------------------------
1               3000           09:30:00              1                    1
1               3000           11:30:00              0                    2
1               3000           12:00:00              1                    3
1               3000           14:00:00              0                    4
1               3000           18:30:00              1                    5
1               3000           20:30:00              0                    6
1               4000           05:00:00              1                    1 
1               4000           13:30:00              0                    2
1               4000           16:30:00              1                    3
1               4000           18:30:00              0                    4

What I want to do is select SCHEDULE_TIME for the last 2 IDX's where DEV_ID is 3000, so I would like to save 18:30:00 and 20:30:00 in a variables, some examples of statements Ive tried are:

select SCHEDULE_TIME from ARRAY_BAC_SCH_Schedule order by IDX desc limit 1 where DEV_ID = 3000
select SCHEDULE_TIME from ARRAY_BAC_SCH_Schedule order by IDX desc limit (1,1) where DEV_ID = 3000

SELECT TOP 1 SCHEDULE_TIME FROM ARRAY_BAC_SCH_Schedule WHERE DEV_ID = 3000 ORDER BY IDX DESC

Right now Im just worrying about how to get the select statement to work in Query tool before I implement it in the java side. Thanks, Beef.

Answer 1

For SQL Server you should use

SELECT TOP 2 SCHEDULE_TIME from (select SCHEDULE_TIME FROM ARRAY_BAC_SCH_Schedule WHERE DEV_ID = 3000 ORDER BY IDX DESC) as inner

like Hemal told you.

Be careful with queries like

select TOP 2 SCHEDULE_TIME FROM ARRAY_BAC_SCH_Schedule WHERE DEV_ID = 3000 ORDER BY IDX DESC

because that is wrong. SQL Server does the top and then the order.

In PostgreSQL or MySQL you should use limit and the end of the query. The limit is after the where part.

In Oracle you should use rownum inside the where part.

Answer 2

Maybe I'm missing something. Is there a reason you wouldn't just run:

select SCHEDULE_TIME from ARRAY_BAC_SCH_Schedule order by IDX desc limit 2 where DEV_ID = 3000

This should return 2 rows, containing 20:30:00 and 18:30:00.

Answer 3

if it is mysql then

 select SCHEDULE_TIME from ARRAY_BAC_SCH_Schedule where DEV_ID = 3000 order by IDX desc limit 2

Answer 4

I think

SELECT TOP 2 * from (select SCHEDULE_TIME FROM ARRAY_BAC_SCH_Schedule WHERE DEV_ID = 3000 ORDER BY IDX DESC) as inner

Answer 5

The specifics will vary a little based on your DB, but your query should look something like this:

SELECT TOP 2 SCHEDULE_TIME 
FROM ARRAY_BAC_SCH_Schedule
WHERE DEV_ID = 3000
ORDER BY IDX Desc

Or, on one line:

SELECT TOP 2 SCHEDULE_TIME FROM ARRAY_BAC_SCH_Schedule WHERE DEV_ID = 3000 ORDER BY IDX Desc

Answer 6

You can do that with subquerys:

select * from array_bac_sch_schedule where (value_enum,idx) in (select value_enum,idx from array_bac_sch_schedule where dev_id=3000) order by schedule_time desc limit 2;

I took value_enum and idx as primary key.