MariaDB's ORDER BY clause does not sort ascending? - sorting

I have the below simple SQL, which is executed against my MariaDB database.
The expected behavior is that the result is sorted by 'day' ASCENDING. However, when executed, the results are sorted in DESCENDING order. Very strange.
SELECT *
FROM
(
SELECT `day`,`count`
FROM
(
SELECT
DATE(`date`) AS `day`,
COUNT(*) as `count`
FROM `message` m
GROUP BY DATE(`date`)
ORDER BY `day` DESC, `count` DESC
) AS q
ORDER BY `day` ASC
) AS q
If I comment out the ORDER BY inside the inner query, the outer ORDER BY works correctly and sorts the results in ascending order without problem.
The problem I have is that the code inside the inner loop is generated code, so I can't remove that inner ORDER BY.
Why does MariaDB behave in this way? Is there some way to change the outer ORDER BY so that it gets the priority is deserves?
Note: I am using MariaDB version: 10.0.24-MariaDB

So, i worked it out.
According to MariaDB, the SQL standard does not require the ORDER BY of a subquery to be respected (unless it would affect the actual rows returned):
https://mariadb.com/kb/en/library/why-is-order-by-in-a-from-subquery-ignored/
If I move the ORDER BY to the very outside query, then it works as expected.

Related

How to add decode but also have count, group by and order by - not a group by expression

I'm rather new to Oracle. I'm trying to do a count of ports for a vendor/model. However, I only want ones with port_addr_status of 3 or 4. For some reason, I'm getting error
ORA-00979 not a group by expression
This is what I have so far. It works without the decode part, but I don't think the part with pi.port_addr.status in ('3','4') works without it. I'm open to working around that issue as well.
select
count(pi.port) as cnt, d.VENDOR, trim(d.model) as model,
decode(pi.PORT_ADDR_STATUS, '1', 'Unassigned', '2','Pending','3','In Service',
'4','Pending Disco', '5','Trouble', '6','Reserved',
'7','Reserved Capacity', pi.PORT_ADDR_STATUS)
from
table1 pi,
table2 d,
table3 c
where
pi.id = d.id and
pi.circuit_id = c.circuit_id
and pi.port_addr_status in ('3','4')
and (d.dslam_type_desc not in ('AGGREGATOR') or d.dslam_type_desc is null)
and d.DSLAM not like '%#%'
group by
d.VENDOR, d.model --, trim(d.model), pi.RACK, pi.SHELF, pi.SLOT, pi.PORT, pi.BROADBAND_CIRCUIT_ID, d.DSLAM,
order by
d.VENDOR asc, cnt desc
This is sample output:
1031 Adtran TA5000
10 Adtran TA1248V
3 Adtran TA1248
Since the decoded port type is not required in your output, just remove it from the select list. Group By should include everything in the select list except the aggregate functions. The below query should do the job:
select
count(pi.port) as cnt, d.VENDOR, trim(d.model) as model
from
table1 pi,
table2 d,
table3 c
where
pi.id = d.id and
pi.circuit_id = c.circuit_id
and pi.port_addr_status in ('3','4')
and (d.dslam_type_desc not in ('AGGREGATOR') or d.dslam_type_desc is null)
and d.DSLAM not like '%#%'
group by
d.VENDOR, trim(d.model)
order by
d.VENDOR asc, cnt desc
Note that the filter down to specific port types is achieved here:
and pi.port_addr_status in ('3','4')
in the where clause - the decode statement in your original query did nothing to solve your requirements and was the direct cause of the error. In a basic aggregate query like this, group by should have every item that is in the select list that is not an aggregate function.
You might use decode statement in the select list with an aggregation function preferably max as
max( decode(pi.PORT_ADDR_STATUS, '1', 'Unassigned', '2','Pending', .... )
The reason you're getting that error is:
when using a GROUP BY clause you are asking the DBMS to give you a single row corresponding to your GROUP BY list
in your case, you are asking for one row per (Vendor, Model) combination
since each of these rows represents possibly many "underlying" rows (say, e.g. 5 rows for Vendor=A and Model=B), the only other fields you can have in the select list must be aggregates (that's why the "count" field works, it counts the rows, i.e. it can take many row values and return a single value)
the DECODE function is not an aggregate function - it can't "collapse" multiple values into one value (like, say, MAX() can)
It looks to me as if your DECODE function returns strings, so I recommend you aggregate the strings with the LISTAGG function (so if your 5 rows have values of 'asdf', 'fdsa', 'qwer', 'rewq', and 'zxcv' the LISTAGG function would return a single string: 'asdf,fdsa,qwer,rewq,zxcv')
So you would replace your DECODE(...) call with, e.g. LISTAGG(DECODE(...), ',')
Reference for LISTAGG function: https://docs.oracle.com/cd/E11882_01/server.112/e41084/functions089.htm#SQLRF30030

Using TOP in ORACLE SQL 9

Hello I'am very new to writing SQL and I am trying to find the appropriate way to use TOP in Oracle SQl 9:
My example:
select * from example e, test t
where e.id = t.id
and country = 'USA'
order by state ASC;
What I am trying to do is take the bottom 20 % of my query but I know you cannot use TOP. After researching I still have not found an applicable answer. I know you have to first order them but am unsure of how to then take the bottom 20%(which would be TOP since the order is ASC)
In general (like if you want the top or bottom 17.2% of the rows) you can use row_number() and count() (analytic functions) to get the result.
20% is easier - you are looking for the top (or bottom) quintile. For this, you can use the ntile() function, like so:
select [column_names]
from (
select e.*, t.*, ntile(5) over (order by state) as nt
from ..... etc
)
where nt = 1;
The subquery is your query. The column_names in the outer query are whatever you actually need; you could also use select * but that will show the ntile too (which will be 1 in all rows).
If sorting something in ASCending order gives us the top set then surely sorting in DESCending order can give us the bottom set.
This solution uses the function NTILE() to divide the records into five buckets. The first bucket is the set we want (because sorted in descending order). Sorting in ascending order and taking the fifth quintile would have the same outcome.
select * from (
select e.*
, t.*
, ntile(5) over (order by state desc) nt
from example e, test t
where e.id = t.id
and country = 'USA'
)
where nt = 1
order by state desc
/
You don't say what your sort criteria are, so I've guessed.

Using PARTITION BY and the order is messing up when I insert. Why?

I wanted to order the employees by time they started an assignment, so that the results would look like this:
So I am using a query similar to:
SELECT a.employeename, b.assignmenttime, ROW_NUMBER() OVER (PARTITION BY a.employeename order by b.assignmenttime) sequence
FROM emplyee a, tasks b
WHERE a.id = b.id
ORDER BY a.employeename, b.assignmenttime
This is inside a procedure and every time the procedure gets called I want the results to be written to a table.
So I have:
INSERT INTO MyTable (Emp,Time,Sequence)
SELECT a.employeename, b.assignmenttime, ROW_NUMBER() OVER (PARTITION BY a.employeename order by b.assignmenttime) sequence
FROM emplyee a, tasks b
WHERE a.id = b.id
ORDER BY a.employeename, b.assignmenttime;
commit;
This is all fine except when the records are written to the table the order gets messed up sometimes and I end up with
As you can see the sequence is not in order. A normal query always returns the records in the right order but why when I call the procedure the records get written out of order in the table? What do I have to do to fix this? Using oracle 10g

Vertica subquery with limit

I found problem in writing subquery with limit 1 to get the top record.
Here is my problem example.
Table Master(id,set)
Table Detail(id,set,code)
i am trying to get the latest code for each set in Master table.
Following is the query which i tried but got an error that limit 1 is not supported for correlated subqueries and it should contain GROUP By clause.
select id,set,(select code from detail where set=master.set order by id desc limit 1) from master;
And the result wolud be like
please help me if this is wrong way, i am new to this vertica database.
thnk you.
I'm not sure about that particular error, but you can use the rank() analytic function to produce results like this:
select id, set, code from (
select M.id, D.set, D.code, rank() over (partition by D.set order by D.id desc) as rank
from detail as D
right outer join master as M
on D.set = M.set) as ranks
where rank = 1
order by id;
The inner subquery uses the rank() function to assign a rank to each row within a set. The outer query just picks out rows with rank 1.

Oracle: MIN() Statement causes empty row returns

I'm having a small issue with sorting the data returned from a query, with the aim of getting the oldest updated value in dataset so that I can update only that record. Here's what I'm doing:
WHERE ROWNUM = 1 AND TABLE1.ID != V_IGNOREID
AND TABLE1.LASTREADTIME = (SELECT MIN(TABLE1.LASTREADTIME) FROM TABLE1)
ORDER BY TABLE1.LASTREADTIME DESC;
It makes no difference as to whether the ORDER BY statement is included or not. If I only use the ROWNUM and equality checks, I get data, but it alternates between only two rows, which is why I'm trying to use the LASTREADTIME data (so that I can modify more than these two rows). Anybody have any thoughts on this, or any suggestions as to how I can use the MIN function effectively?
Cheers
select * from (
-- your original select without rownum and with order by
)
WHERE ROWNUM = 1
EDIT some explanation
I think the order by clause is applied on the resultset after the where clause. So if the rownum = 1 is in the same select statement with the order by, then it will be applied first and the order by will order only 1 row, which will be the first row of the unordered resultset.

Resources