Is it possible to use two NamedParameterStatement for a single query?
I need to find the ids (Primary and foreign key) for the given value using one NamedParameterStatement, and then all other details related to the ids from other tables.
for example
select code1, code2 code 3
from master table where id in (select id from master table where (date between or any other values))
The description for other codes are in other table
Here I need to pass the result of inner query to the outer query ( I may get the many ids). And I know how to pass the result to another query in JDBC?
Related
I am new to Hive and have some problems. I try to find a answer here and other sites but with no luck... I also tried many different querys that come to my mind, also without success.
I have my source table and i want to create new table like this.
Were:
id would be number of distinct counties as auto increment numbers and primary key
counties as distinct names of counties (from source table)
You could follow this approach.
A CTAS(Create Table As Select)
with your example this CTAS could work
CREATE TABLE t_county
ROW FORMAT DELIMITED FIELDS TERMINATED BY ','
STORED AS TEXTFILE AS
WITH t AS(
SELECT DISTINCT county, ROW_NUMBER() OVER() AS id
FROM counties)
SELECT id, county
FROM t;
You cannot have primary key or foreign keys on Hive as you have primary key on RBDMSs like Oracle or MySql because Hive is schema on read instead of schema on write like Oracle so you cannot implement constraints of any kind on Hive.
I can not give you the exact answer because of it suppose to you must try to do it by yourself and then if you have a problem or a doubt come here and tell us. But, what i can tell you is that you can use the insertstatement to create a new table using data from another table, I.E:
create table CARS (name string);
insert table CARS select x, y from TABLE_2;
You can also use the overwrite statement if you desire to delete all the existing data that you have inside that table (CARS).
So, the operation will be
CREATE TABLE ==> INSERT OPERATION (OVERWRITE?) + QUERY OPERATION
Hive is not an RDBMS database, so there is no concept of primary key or foreign key.
But you can add auto increment column in Hive. Please try as:
Create table new_table as
select reflect("java.util.UUID", "randomUUID") id, countries from my_source_table;
I know that ROWID is distinct for each row in different tables.But,I am seeing somewhere that two tables are being merged using rowid.So,I also tried to see it,but I am getting the blank output.
I have person table which looks as:
scrowid is the column which contains rowid as:
alter table ot.person
add scrowid VARCHAR2(200) PRIMARY KEY;
I populated this person table as:
insert into ot.person(id,name,age,scrowid)
select id,name, age,a.rowid from ot.per a;
After this I also created another table ot.temp_person by same steps.Both table has same table structure and datatypes.So, i wanted to see them using inner join and I tried them as:
select * from ot.person p inner join ot.temp_person tp ON p.scrowid=tp.scrowid
I got my output as empty table:
Is there is any possible way I can merge two tables using rowid? Or I have forgotten some steps?If there is any way to join these two tables using rowid then suggest me.
Define scrowid as datatype ROWID or UROWID then it may work.
However, in general the ROWID may change at any time unless you lock the record, so it would be a poor key to join your tables.
I think perhaps you misunderstood the merging of two tables via rowid, unless what you actually saw was a Union, Cross Join, or Full Outer Join. Any attempt to match rowid, requardless of you define it, doomed to fail. This results from it being an internal definition. Rowid in not just a data type it is an internal structure (That is an older version of description but Oracle doesn't link documentation versions.) Those fields are basically:
- The data object number of the object
- The data block in the datafile in which the row resides
- The position of the row in the data block (first row is 0)
- The datafile in which the row resides (first file is 1). The file
number is relative to the tablespace.
So while it's possible for different tables to have the same rowid, it would be exteremly unlikely. Thus making an inner join on them always return null.
Just want to know is this possible.
Say that if i have value 'X' and iam sure that this is referenced in some other tables as PK value but not sure about exactly which table is that, so i would like to know the list of those tables.
Pseudo query of above what i mentioned
SELECT TABLE_NAME FROM DBA_TABLES WHERE <<ATLEAST ONE OF THE TABLE ROW PK VALUE IS MATCHING EQUAL TO 'X'>>;
I have a table A and a table B.
Table B has a relationship with A with the key a_id.
I already created the document in a in table A.
I'm wondering how to insert data in a single query using a doc in table B with foreign key A.
r.db('DB').table('B').insert([{
'b_data': ...,
'a_id': r.db('DB').table('a').filter(r.row['name'] == 'some_name')
} for p in a]).run(conn)
You are on the right track, but ReQL differs from the logic of SQL in that it is usually more like a flow. So your query needs to start with the source of the data so it can flow into the insert portion. So here is a version of what I think you want (in Python format):
r.db('DB').table('a').filter({'name':'some_name}).for_each(
r.db('DB').table('b').insert(
{'name':r.row['name'],'b_data':'something'}
)
).run(conn)
I recently was reading about Oracle Index Organized Tables (IOTs) but am not sure I quite understand WHEN to use them. So I have a small table:
create table categories
(
id VARCHAR2(36),
group VARCHAR2(100),
category VARCHAR2(100
)
create unique index (group, category, id) COMPRESS 2;
The id column is a foreign key from another table entries and my common query is:
select e.id, e.time, e.title from entries e, categories c where e.id=c.id AND e.group=? AND c.category=? ORDER by e.time
The entries table is indexed properly.
Both of these tables have millions (16M currently) of rows and currently this query really stinks (note: I have it wrapped in a pagination query also so I only get back the first 20, but for simplicity I omitted that).
Since I am basically indexing the entire table, does it make sense to create this table as an IOT?
EDIT by popular demand:
create table entries
(
id VARCHAR2(36),
time TIMESTAMP,
group VARCHAR2(100),
title VARCHAR2(500),
....
)
create index (group, time) compress 1;
My real question I dont think depends on this though. Basically if you have a table with few columns (3 in this example) and you are planning on putting a composite index on all three rows is there any reason not to use an IOT?
IOTs are great for a number of purposes, including this case where you're gonna have an index on all (or most) of the columns anyway - but the benefit only materialises if you don't have the extra index - the idea is that the table itself is an index, so put the columns in the order that you want the index to be in. In your case, you're accessing category by id, so it makes sense for that to be the first column. So effectively you've got an index on (id, group, category). I don't know why you'd want an additional index on (group, category, id).
Your query:
SELECT e.id, e.time, e.title
FROM entries e, categories c
WHERE e.id=c.id AND e.group=? AND c.category=?
ORDER by e.time
You're joining the tables by ID, but you have no index on entries.id - so the query is probably doing a hash or sort merge join. I wouldn't mind seeing a plan for what your system is doing now to confirm.
If you're doing a pagination query (i.e. only interested in a small number of rows) you want to get the first rows back as quick as possible; for this to happen you'll probably want a nested loop on entries, e.g.:
NESTED LOOPS
ACCESS TABLE BY ROWID - ENTRIES
INDEX RANGE SCAN - (index on ENTRIES.group,time)
ACCESS TABLE BY ROWID - CATEGORIES
INDEX RANGE SCAN - (index on CATEGORIES.ID)
Since the join to CATEGORIES is on ID, you'll want an index on ID; if you make it an IOT, and make ID the leading column, that might be sufficient.
The performance of the plan I've shown above will be dependent on how many rows match the given "group" - i.e. how selective an average "group" is.
Have you looked at dba-oracle.com, asktom.com, IOUG, another asktom.com?
There are penalties to pay for IOTs - e.g., poorer insert performance
Can you prototype it and compare performance?
Also, perhaps you might want to consider a hash cluster.
IOT's are a trade off. You are getting access performance for decreased insert/update performance. We typically use them for reference data that is batch loaded daily and not updated during the day. This is not to say it's the only way to use them, just how we use them.
Few things here:
You mention pagination - have you considered the first_rows hint?
Is that the order your index is in, with group as the first field? If so I'd consider moving ID to be the first column since that index will not be used.
foreign keys should have an index on the column. Consider addind an index on the foreign key (id column).
Are you sure it's not the ORDER BY causing slowness?
What version of Oracle are you using?
I ASSUME there is a primary key on table entries for field id, correct?
Why the WHERE condition does not include "c.group = e.group" ?
Try to:
Remove the order by condition
Change the index definition from "create unique index (group,
category, id)" to "create unique index (id, group, category)"
Reorganise table categories as an IOT on (group, category, id)
Reorganise table categories as an IOT on (id, group, category)
In each of the above case use EXPLAIN PLAN to review the cost