im getting an column ambiguously defined im trying to write a query to get data from three different tables my query is
select flight_no,
country_code,
destination,
depatue_time,
arrival_time
from flight,
country,
flight_availibility
where country_code='MCT'
and destination='IND'
order by flight_no;
and im getting error can anybody tell me what is wrong!!!
The error is telling you that you're asking for a column that shares a name from more than one of those tables. You want 'flight_no' - but, there may be a column named 'flight_no' in both the flight and country tables.
To avoid this, use aliases in your FROM clause.
Example
select a.col1, b.col1
from table1 a, table2 b
where a.id = b.id;
This isn't ambiguous, because you're explicitly telling Oracle which columns named 'col1' you want - you're not making it guess.
This isn't part of your question, but your query as you write it will cause the database to join every record in each table to every other record in the other two tables. This is known as a Cartesian Join or Product.
Is it necessarily wrong? Maybe not. But 99% of the time, it's not what you want. You only want the rows that 'match' - so use a WHERE clause and filter out the rows.
Or go the ANSI JOIN way and do it in the FROM clause.
The error occurred because same column name having in the 2 tables , so when we run the query using only column name , this error is occurring
Try the below to avoid those issue :
select a.flight_no,b.country_code,a.destination,c.depature_time,c.arrival_time
from
flight a ,
country b
Related
I currently face the problem, that I get an exception when executing a query generated by the entity framework.
The query worked until I've joined another table using .include() to the existing entity. Now, whenever I execute the query, I get an Oracle error ORA-12704 character set mismatch.
I narrowed the problem down to the following:
Before joining the table, the generated SQL is a simple query with some join statements. After joining another table, the generated SQL cointains two subqueries which are combined using UNION ALL. In one of the subqueries, a lot of helper-columns are selected.
They look like this:
SELECT
... some other columns...
TO_NUMBER(NULL) AS C1,
TO_CHAR(NULL) AS C2,
...
If I remove those columns and also the corresponding ones in the other subquery, no error is thrown. When I replace the columns with NULL instead of TO_XXX(NULL), the query also works as expected.
Is there any way force the entity-framework not to use these problematic casts?
The problem is caused with the usage of a NVARCHAR2 column in combination with the function TO_CHAR (that returns VARCHAR2 data type) as illustrated below
create table tab
(txt nvarchar2(10));
select txt from tab
union all
select to_char(null) from dual;
ORA-12704: character set mismatch
So your goal is to motivate the tool to generate a query that uses either TO_NCHAR(null) or cast(null as nvarchar2(10)) - both will work.
To do this, you need to add the following data-annotation to the property of the corresponding entity:
[Column(TypeName = "NVARCHAR2")]
The given TypeName must match with the type of the column in the database.
After this addition, the entityframework will generate the correct casts. In this case, the following cast ist generated:
SELECT
...
TO_NCHAR(NULL),
...
You should see no problem with the to_number(null) if the corresponding UNIONcolumn is of a number datatype.
I am trying to subtract two columns and fetch the result if the difference is greater then 100 in hive. I have written the following query:
select District.ID,Year,(volume_IN-volume_OUT) as d1 from petrol where d1>100;
but I am getting error.
The table column names are:
District.ID, Distributer name, volume_IN ,volume_OUT, Year
Please help me, Is there any error in the query. I am new to the hive.
One of the Limitations of hive is you cannot refer the alias you used in the same query
Try writing a subquery, may be something like below
select * from (select District_ID,year, (volume_IN-volume_OUT) as d1 from petrol) t1 where d1>100;
So I am having a big table of AbstractID, SentenceID, WordID, and Word. Some words show in multiple files. I would like to count how many files every word shows, and then create a new table of with Word and Count. Below is a piece of my data.
My sql query is below:
CREATE TABLE WORDLIST(WORD, TOTALCOUNT) AS
(
SELECT WORD FROM ASSIGNMENT2 WHERE
(
SELECT WORD, COUNT(*) FROM (select DISTINCT FILEID, WORD FROM ASSIGNMENT2)
GROUP BY WORD ORDER BY COUNT(*) DESC));
It is giving me an error:
"Error report:
SQL Error: ORA-00936: missing expression
00936. 00000 - "missing expression"
*Cause:
*Action:"
How do I correct this? Thanks.
You're rather overcomplicating the query. The error is because your outer where clause doesn't have a condition; you're selecting multiple things, which isn't right anyway, but then not comparing those to anything. And you don't need to enclose the query in a set of parentheses.
You can just do:
CREATE TABLE WORDLIST (WORD, TOTALCOUNT) AS
SELECT WORD, COUNT(DISTINCT FILEID)
FROM ASSIGNMENT2
GROUP BY WORD;
There's no point ordering the query as it won't affect future queries against the new table - you still have to order those, as there is no inherent order of rows within the table. (And I think an order by will cause an error in a create-as statement, but can't immediately check that).
Creating a table to hold this information seems odd though as it will go out of date quickly. Perhaps you wanted a view really?
I have a requirement to do a nested select within a where clause in a Hive query. A sample code snippet would be as follows;
select *
from TableA
where TA_timestamp > (select timestmp from TableB where id="hourDim")
Is this possible or am I doing something wrong here, because I am getting an error while running the above script ?!
To further elaborate on what I am trying to do, there is a cassandra keyspace that I publish statistics with a timestamp. Periodically (hourly for example) this stats will be summarized using hive, once summarized that data will be stored separately with the corresponding hour. So when the query runs for the second time (and consecutive runs) the query should only run on the new data (i.e. - timestamp > previous_execution_timestamp). I am trying to do that by storing the latest executed timestamp in a separate hive table, and then use that value to filter out the raw stats.
Can this be achieved this using hive ?!
Subqueries inside a WHERE clause are not supported in Hive:
https://cwiki.apache.org/confluence/display/Hive/LanguageManual+SubQueries
However, often you can use a JOIN statement instead to get to the same result:
https://karmasphere.com/hive-queries-on-table-data#join_syntax
For example, this query:
SELECT a.KEY, a.value
FROM a
WHERE a.KEY IN
(SELECT b.KEY FROM B);
can be rewritten to:
SELECT a.KEY, a.val
FROM a LEFT SEMI JOIN b ON (a.KEY = b.KEY)
Looking at the business requirements underlying your question, it occurs that you might get more efficient results by partitioning your Hive table using hour. If the data can be written to use this factor as the partition key, then your query to update the summary will be much faster and require fewer resources.
Partitions can get out of hand when they reach the scale of millions, but this seems like a case that will not tease that limitation.
It will work if you put in :
select *
from TableA
where TA_timestamp in (select timestmp from TableB where id="hourDim")
EXPLANATION : As > , < , = need one exact figure in the right side, while here we are getting multiple values which can be taken only with 'IN' clause.
I am new to Oracle and working with a fairly large database. I would like to perform a query that will select the desired columns, order by a certain column and also limit the results. According to everything I have read, the below query should be working but it is returning "ORA-00918: column ambiguously defined":
SELECT * FROM(SELECT * FROM EAI.EAI_EVENT_LOG e,
EAI.EAI_EVENT_LOG_MESSAGE e1 WHERE e.SOURCE_URL LIKE '%.XML'
ORDER BY e.REQUEST_DATE_TIME DESC) WHERE ROWNUM <= 20
Any suggestions would be greatly appreciated :D
The error message means your result set contains two columns with the same name. Each column in a query's projection needs to have a unique name. Presumably you have a column (or columns) with the same name in both EAI_EVENT_LOG and EAI_EVENT_LOG_MESSAGE.
You also want to join on that column. At the moment you are generating a cross join between the two tables. In other words, if you have a hundred records in EAI_EVENT_LOG and two hundred records EAI_EVENT_LOG_MESSAGE your result set will be twenty thousand records (without the rownum). This is probably your intention.
"By switching to innerjoin, will that eliminate the error with the
current code?"
No, you'll still need to handle having two columns with the same name. Basically this comes from using SELECT * on two multiple tables. SELECT * is bad practice. It's convenient but it is always better to specify the exact columns you want in the query's projection. That way you can include (say) e.TRANSACTION_ID and exclude e1.TRANSACTION_ID, and avoid the ORA-00918 exception.
Maybe you have some columns in both EAI_EVENT_LOG and EAI_EVENT_LOG_MESSAGE tables having identical names? Instead of SELECT * list all columns you want to select.
Other problem I see is that you are selecting from two tables but you're not joining them in the WHERE clause hence the result set will be the cross product of those two table.
You need to stop using SQL '89 implicit join syntax.
Not because it doesn't work, but because it is evil.
Right now you have a cross join which in 99,9% of the cases is not what you want.
Also every sub-select needs to have it's own alias.
SELECT * FROM
(SELECT e.*, e1.* FROM EAI.EAI_EVENT_LOG e
INNER JOIN EAI.EAI_EVENT_LOG_MESSAGE e1 on (......)
WHERE e.SOURCE_URL LIKE '%.XML'
ORDER BY e.REQUEST_DATE_TIME DESC) s WHERE ROWNUM <= 20
Please specify a join criterion on the dotted line.
Normally you do a join on a keyfield e.g. ON (e.id = e1.event_id)
It's bad idea to use select *, it's better to specify exactly which fields you want:
SELECT e.field1 as customer_id
,e.field2 as customer_name
.....