I have question about "Subquery in Order by clause". The below request returns the error. Is it means that Subquery in Order by clause must be scalar?
select *
from employees
order by (select * from employees where first_name ='Steven' and last_name='King');
Error:
ORA-00913: too many values
00913. 00000 - "too many values"
Yes, it means that if you use a subquery in ORDER BY it must be scalar.
With select * your subquery returns multiple columns and the DBMS would not know which of these to use for the sorting. And if you selected one column only, you would still have to make sure you only select one row of course. (The difference is that Oracle sees the too-many-columns problem immediately, but detect too many rows only when fetching the data.)
This would be allowed:
select * from employees
order by (select birthdate from employees where employee_id = 12345);
This is a scalar query, because it returns only one value (one column, one row). But of course this still makes as little sense as your original query, because the subquery result is independent from the main query, i.e. it returns the same value for every row in the table and thus no sorting takes effect.
A last remark: A subquery in ORDER BY makes very seldomly sense, because that would mean you order by something you don't display. The exception is when looking up a sortkey. E.g.:
select *
from products p
where type = 'shirt' and color = 'blue' and size in ('S', 'M', 'L', 'XL')
order by (select sortkey from sizes s where s.size = p.size);
It means that valid options for ORDER BY clause can be
expression,
position or
column alias
A subquery is neither of these.
Related
Am trying to list top 3 records from atable based on some amount stored in a column FTE_TMUSD which is of varchar datatype
below is the query i tried
SELECT *FROM
(
SELECT * FROM FSE_TM_ENTRY
ORDER BY FTE_TMUSD desc
)
WHERE rownum <= 3
ORDER BY FTE_TMUSD DESC ;
o/p i got
972,9680,963 -->FTE_TMUSD values which are not displayed in desc
I am expecting an o/p which will display the top 3 records of values
That should work; inline view is ordered by FTE_TMUSD in descending order, and you're selecting values from it.
What looks suspicious are values you specified as the result. It appears that FTE_TMUSD's datatype is VARCHAR2 (ah, yes - it is, you said so). It means that values are sorted as strings, not numbers - and it seems that you expect numbers. So, apply TO_NUMBER to that column. Note that it'll fail if column contains anything but numbers (for example, if there's a value 972C).
Also, an alternative to your query might be use of analytic functions, such as row_number:
with temp as
(select f.*,
row_number() over (order by to_number(f.fte_tmusd) desc) rn
from fse_tm_entry f
)
select *
from temp
where rn <= 3;
I have a table with 3 columns:
table1: ID, CODE, RESULT, RESULT2, RESULT3
I have this SAS code:
data table1
set table1;
BY ID, CODE;
IF FIRST.CODE and RESULT='A' THEN OUTPUT;
ELSE IF LAST.CODE and RESULT NE 'A' THEN OUTPUT;
RUN;
So we are grouping the data by ID and CODE, and then writing to the dataset if certain conditions are met. I want to write a hive query to replicate this. This is what I have:
proc sql;
create table temp as
select *, row_number() over (partition by ID, CODE) as rowNum
from table1;
create table temp2 as
select a.ID, a.CODE, a.RESULT, a.RESULT2, a.RESULT3
from temp a
inner join (select ID, CODE, max(rowNum) as maxRowNum
from temp
group by ID, CODE) b
on a.ID=b.ID and a.CODE=b.CODE
where (a.rowNum=1 and a.RESULT='A') or (a.rowNum=b.maxRowNum and a.RESULT NE 'A');
quit;
There are two issues I see with this.
1) The row that is first or last in each BY group is entirely dependant on the order of rows in table1 in SAS, we aren't ordering by anything. I don't think row order is preserved when translating to a hive query.
2) The SAS code is taking the first row in each BY GROUP or the last, not both. I think that my HIVE query is taking both, resulting in more rows than I want.
Any suggestions or insight on how to improve my query is appreciated. Is it even possible to replicate this SAS code in HIVE?
The SAS code has a by statement (BY ID CODE;), which tells SAS that the set dataset is sorted at those levels. So, not a random selection for first. and last..
That said, we can replicate this in HIVE by using the first_value and last_value window functions.
FIRST.CODE should replicate to
first_value(code) over (partition by Id order by code)fcode
Similarly, LAST.CODE would be
last_value(code) over (partition by Id order by code)lcode
Once you have the fcode and lcode columns, use case when statements for the result column criteria. Like,
case when (code=fcode and result='A') or (code=lcode and result<>'A')
then 1 else 0 end as op_flag
Then the fetch the table with where op_flag = 1
SAMPLE
select id, code, result from (
select *,
first_value(code) over (partition by id order by code)fcode,
last_value(code) over (partition by id order by code)lcode
from footab) f
where (code=fcode and result='A') or (code=lcode and result<>'A')
Regarding point 1) the BY group processing requires the input data to be sorted or indexed on BY variables, so though the code contains no ordering, the source data is processed in order. If the input data was not indexed/sorted, SAS will throw error.
Regarding this, possible differences are on rows with same values of BY variables, especially if the RESULT is different.
In SAS, I would pre-sort data by ID, CODE, RESULT, then use BY ID CODE in order to not be influenced by order of rows.
Regarding 2) FIRST and LAST can be both true in SAS. Since your condition for first and last on RESULT is different, I guess this is not a source of differences.
I guess you could add another field as
row_number() over (partition by ID, CODE desc) as rowNumDesc
to detect last row with rowNumDesc = 1 (so that you skip the join).
EDIT:
I think the two programs above both include random selection of rows for groups with same values of ID and CODE variables, especially with same values of RESULT. But you should get same number of rows from both. If not, just debug it.
However the random aspect in SAS code/storage is based on physical order of rows, while the ROW_NUMBERs randomness within a group will be influenced by the implementation of the function in the engine.
I have two hive tables (t1 and t2) that I would like to compare. The second table has 5 additional columns that are not in the first table. Other than the five disjoint fields, the two tables should be identical. I am trying to write a query to check this. Here is what I have so far:
SELECT * FROM t1
UNION ALL
select * from t2
GROUP BY some_value
HAVING count(*) == 2
If the tables are identical, this should return 0 records. However, since the second table contains 5 extra fields, I need to change the second select statement to reflect this. There are almost 60 column names so I would really hate to write it like this:
SELECT * FROM t1
UNION ALL
select field1, field2, field3,...,fieldn from t2
GROUP BY some_value
HAVING count(*) == 2
I have looked around and I know there is no select * EXCEPT syntax, but is there a way to do this query without having to explicity name each column that I want included in the final result?
You should have used UNION DISTINCT for the logic you are applying.
However, the number and names of columns returned by each select_statement have to be the same otherwise a schema error is thrown.
You could have a look at this Python program that handles such comparisons of Hive tables (comparing all the rows and all the columns), and would show you in a webpage the differences that might appear: https://github.com/bolcom/hive_compared_bq
To skip the 5 extra fields, you could use the "--ignore-columns" option.
The easiest way to ask my question is with a Hypothetical Scenario.
Lets say we have 3 tables. Singapore_Prices, Produce_val, and Bosses_unreasonable_demands.
So Prices is a pretty simple table. Item column containing a name, and a Price column containing a number.
Produce_Val is also simple 2 column table. Type column containing what type the produce is (Fruit or veggie) and then Name column (Tomato, pineapple, etc.)
The Bosses_unreasonable_demands only contains one column, Fruit, which CAN contain the names of some fruits.
OK? Ok.
SO, My boss wants me to write a query that returns the prices for every fruit in his unreasonable demands table. Simple enough. BUT, if he doesn't have any entries in his table, he just wants me to output the prices of ALL fruits that exist in produce_val.
Now, assuming I don't know where the DBA who designed this silly hypothetical system lives (and therefore can't get him to fix this), our query would look like this:
if <Logic to determine if Bosses demands are empty>
Then
select Item, Price
from Singapore_Prices
where Item in (select Fruit from Bosses_Unreasonable_demands)
Else
select Item, Price
from Singapore_Prices
where Item in (select Name from Produce_val where type = 'Fruit')
end if;
(Well, we'd select those into a variable, and then output the variable, probably with bulk-collect shenanigans, but that's not important)
Which works. It is entirely functional, and won't be slow, even if we extend it out to 2000 other stores other than Singapore. (Well, no slower than anything else that touches 2000 some tables) BUT, I'm still doing two different select statements that are practically identical. My Comp Sci teacher rolls in their grave every time my fingers hit ctrl-V. I can cut this code in half and only do one select statement. I KNOW I can.
I just have no earthly idea how. I can't use cursors as an in statement, I can't use nested tables or varrays, I can't use cleverly crafted strings, I... I just... I don't know. I don't know how to do this. Is there a way? Does it exist?
Or do I have to copy/paste forever?
Your best bet would be dynamic SQL, because you can't parameterize table or column names.
You will have a SQL query template, have a logic to determine tables and columns that you want to query, then blend them together and execute.
Another aproach, (still a lot of ctrl-v like code) is to use set construction UNION ALL:
select 1st query where boss_condition
union all
select 2nd query where not boss_condition
Try this:
SELECT *
FROM (SELECT s.*, 'BOSS' AS FRUIT_SOURCE
FROM BOSSES_UNREASONABLE_DEMANDS b
INNER JOIN SINGAPORE_FRUIT_LIST s
ON s.ITEM = b.FRUIT
CROSS JOIN (SELECT COUNT(*) AS BOSS_COUNT
FROM BOSSES_UNREASONABLE_DEMANDS)) x
UNION ALL
(SELECT s.*, 'NORMAL' AS FRUIT_SOURCE
FROM PRODUCE_VAL p
INNER JOIN SINGAPORE_FRUIT_LIST s
ON (s.ITEM = p.NAME AND
s.TYPE = 'Fruit')
CROSS JOIN (SELECT COUNT(*) AS BOSS_COUNT
FROM BOSSES_UNREASONABLE_DEMANDS)) n
WHERE (BOSS_COUNT > 0 AND FRUIT_SOURCE = 'BOSS') OR
(BOSS_COUNT = 0 AND FRUIT_SOURCE = 'NORMAL')
Share and enjoy.
I think you can use nested tables. Assume you have a schema-level nested table type FRUIT_NAME_LIST (defined using CREATE TYPE).
SELECT fruit
BULK COLLECT INTO my_fruit_name_list
FROM bosses_unreasonable_demands
;
IF my_fruit_name_list.count = 0 THEN
SELECT name
BULK COLLECT INTO my_fruit_name_list
FROM produce_val
WHERE type='Fruit'
;
END IF;
SELECT item, price
FROM singapore_prices
WHERE item MEMBER OF my_fruit_name_list
;
(or, WHERE item IN (SELECT column_value FROM TABLE(CAST(my_fruit_name_list AS fruit_name_list)) if you like that better)
I am trying to understand why this would throw an error-
select count((select 1 br from dual
union
select 2 br from dual))
from dual;
ORA-01427: single-row subquery returns more than one row
But This won't-
select count(br)
from (select 1 br from dual
union
select 2 br from dual);
BR
----------
2
Take a look at the syntax of COUNT function here:
This function accepts the expression as it's argument.
Now take a look at the definition of the expression here.
An expression is a combination of one or more values, operators, and SQL functions that evaluates to a value.
A value - means single, one, scalar, individual, simple, atomic value
Not many values like a vector, an array, a table or a resultset.
Just one value, like 2 or 10.
The expression can have many forms, could be even a subquery, but SQL restricts this subquery to a special form called a scalar subquery, see this:
expression :=
A scalar subquery is defined here
A scalar subquery expression is a subquery that returns exactly one column value from one row.
Since the subquery in your query returns two rows, it doesn't conforms to the definition of the scalar subquery, and this is the reason of this error:
ORA-01427: single-row subquery returns more than one row
EDIT: Question #2: But isn't count supposed to count the number of rows in a result set?
Yes, of course. Count is one of aggregate functions.
See this chapter: http://docs.oracle.com/cd/E11882_01/server.112/e26088/functions003.htm#SQLRF20035
and also examples here: http://docs.oracle.com/cd/E11882_01/server.112/e26088/statements_10002.htm#SQLRF55380
aggregate functions return a single result row based on groups of rows, rather than on single rows. Aggregate functions can appear in select lists and in ORDER BY and HAVING clauses. They are commonly used with the GROUP BY clause in a SELECT statement, where Oracle Database divides the rows of a queried table or view into groups. In a query containing a GROUP BY clause, the elements of the select list can be aggregate functions, GROUP BY expressions, constants, or expressions involving one of these. Oracle applies the aggregate functions to each group of rows and returns a single result row for each group.
If you omit the GROUP BY clause, then Oracle applies aggregate functions in the select list to all the rows in the queried table or view. You use aggregate functions in the HAVING clause to eliminate groups from the output based on the results of the aggregate functions, rather than on the values of the individual rows of the queried table or view.
In simple words, aggregate functions can only be used in queries with GROUP BY and HAVING clauses, like this:
SELECT count( x )
FROM table
......
GROUP BY yyy
The special case is when you omit GROUP BY:
If you omit the GROUP BY clause, then Oracle applies aggregate functions in the select list to all the rows in the queried table or view.
SELECT count( x )
FROM table
But still, in these queries, count can accept only the expression (the scalar subquery) or * as it's argument.