I have the probably unenviable task of writing a data migration query to populate existing records with a value for a new column being added to a table on a production database. The table has somewhere in the order of 200,000 rows.
The source of the value is in some XML that is stored in the database. I have some XPath that will pull out the value I want, and using extractValue to get the value out seems all good, until the number of records being updated by the query starts getting larger than the few I had in my test DB.
Once the record set grows to some random amount of size, somewhere around 500 rows, then I start getting the error "ORA-19025: EXTRACTVALUE returns value of only one node". Figuring that there was some odd row in the database for which there wasn't a unique result for the XPath, I tried to limit down the records in the query to isolate the bad record. But as soon as I shrunk the record set, the error disappeared. There is actually no row that will return more than one value for this XPath query. It looks like there's something fishy happening with extractValue.
Does anyone know anything about this? I'm not an SQL expert, and even then have spent more time on SQL Server than Oracle. So if I can't get this to work I guess I'm left to do some messing with cursors or something.
Any advice/help? If it helps, we're running 10g on the server. Thanks!
It's almost certain that at least one row from the table with the source XML has an invalid value. Rewrite the query to try and find it.
For example, use the XMLPath predicate that would give you the node in the second position (I don't currently have access to a db with XML objects, so I can't guarantee the following is syntactically perfect):
SELECT SourceKey
, EXTRACTVALUE(SourceXML, '/foo/bar/baz[1]')
, EXTRACTVALUE(SourceXML, '/foo/bar/baz[2]')
FROM SourceTable
WHERE EXTRACTVALUE(SourceXML, '/foo/bar/baz[2]') IS NOT NULL;
Related
I just want to check whether my query is correct. I have written a simple query on one table and against a field in that table where we are looking for all rows where the value in that field is starting with a certain characters and ending in certain characters, but must not contain certain characters in that field's value. Thus -
WHERE field_1 LIKE 'ABC%' AND field_1 LIKE '%XWY' AND field_1 NOT LIKE '%GHI12XY%'
The result is no rows, which is what we wanted, but I am not 100% sure whether the query is spot on and would like other whether this is correct
It looks correct to me. A good idea in all database software development is to create and load one or more test tables with rows that can be used to verify your logic. Then run your query against the test table(s) and see if you get the results you expect. Ideally, the rows in your test table will cover all the possibilities, for example, where you're supposed to get output, and where you're not supposed to get any.
Let's say I have the following 'items' table in my PostgreSQL database:
id
item
value
1
a
10
2
b
20
3
c
30
For some reason I can't control I need to run the following query:
select max(value) from items;
which will return 30 as the result.
At this point, I know that I can find the record that contains that value using simple select statements, etc. That's not the actual problem.
My real questions are:
Does PostgreSQL know (behind the scenes) what's is the ID of that
record, although the query shows only the max value of the column
'value'?
If yes, can I have access to that information and,
therefore, get the ID and other data from the found record?
I'm not allowed to create indexes and sequences, or change way the max value is retrieved. That's a given. I need to work from that point onward and find a solution (which I have, actually, from regular query work).
I'm just guessing that the database knows in which record that information (30) is and that I could have access to it.
I've been searching for an answer for a couple of hours but wasn't able to find anything.
What am I missing? Any ideas?
Note: postgres (PostgreSQL) 12.5 (Ubuntu 12.5-0ubuntu0.20.10.1)
You can simply extract the whole record that contains max(value) w/o bothering about Postgres internals like this:
select id, item, "value"
from items
order by "value" desc
limit 1;
I do not think that using undocumented "behind the scenes" ways is a good idea at all. The planner is smart enough to do exactly what you need w/o extra work.
Given a SELECT statement in Big Query and the Java SDK, what are my options to get the actual column names without fetching the data? I know I can execute the statement and then get the Schema via the TableResult. But is there a way to get the names without fetching data? We have a tool where we run arbitrary queries which are not known upfront and in my code I want to access the result columns by name.
Update: someone flagged this as duplicate of a 7 year old entry. I am however looking for a way to use the Java SDK alone to get the column names, not to do some magic with the query itself or query some metatable.
There are few options but the easiest is to add limit 0 to your query so for example:
SELECT * FROM projectId.datasetId.tableId limit 0
I'm having a table with 6 columns and I want to perform a select query based on all 6 columns, but one column's data is mistyped/incorrect and I get no data returned. What could be used to still have my data returned even though some data is incorrect, but I still want most relevant records to be returned?
Don't know how much this can help you, But you can give a try using SOUNDEX function in SQL server.
Check this link for information on SOUNDEX Function
I use PostgreSQL database and C to connect to it. With a help from dyntest.pgc I can access to number of columns and their (SQL3) types from a result table of a query.
Problem is that when result table is empty, I can't fetch a row to get this data. Does anyone have a solution for this?
Query can be SELECT 1,2,3 - so, I think I can't use INFORMATION SCHEMA for this because there is no base table.
I'm not familiar with ecpg, but with libpq you should be able to call PQnfields to get the number of fields and then call various PQf* routines (like PQftype, PQfname) to get detailed info. Those functions take a PGResult, which you have even if there are no rows.
Problem is that when result table is empty, I can't fetch a row to get this data. Does anyone have a solution for this?
I am not sure to really get what you want, but it seems the answer is in the question. If the table is empty, there are no rows...
The only solution here seems you must wait a non empty result table, and then get the needed informations.