This question already has an answer here:
Alternate method to global temp tables for Oracle Stored Procedure
(1 answer)
Closed 8 years ago.
I need a way to temporarily store and use multiple values returned from an Oracle query. In SQL Server, I stored my values in a temp table, did my work, then dropped the table. I'm discovering the Oracle equivalent isn't as clear cut.
Here's a SQL Server example of what I'm trying to do:
select id into #temp from SomeTable where SomeColumn = 'Some Value'
:
(do whatever I need to do with #temp data)
:
drop table #temp
I can code my way around SQL Server pretty well, but am almost clueless when it comes to Oracle syntax. I've been reading various Oracle references, and they haven't been very helpful. I did read that Oracle temp tables work differently than SQL, and are often not recommended.
I'm looking into the temp table route, but if there's a better way to do this that doesn't use temp tables, I'm all ears. Anyone know a better way to do this in Oracle?
Thanks in advance.
As with many things, that depends. It depends on how much data you'll be retrieving and how you want to use it. If you don't have too much data to work with ("too much" meaning, oh, say, more than a couple thousand rows) and you want to manipulate the data procedurally, i.e. in a PL/SQL procedure or script, AND you don't want to access it using DML, i.e. you don't want to say something like SELECT * FROM your_temp_data... than loading the data into a PL/SQL collection, as #EgorSkriptunoff mentions above, might be a workable solution.
However, if the temp data is large (more than a couple thousand rows) and/or you need to be able to do something like SELECT * FROM your_temp_data... then your best bet it to use Oracle's Global Temp Tables. A GTT is a table which is used to hold data which should only last as long as either a single transaction or a complete session (i.e. as long as you're attached to the database). Documentation here and here, and another write-up on them here.
Share and enjoy.
Related
Is this considered good practice?
Been trying to merge data from 2 different tables (dsb_nb_users_option & dsb_nb_default_options) for the number of users existing on dsb_nb_users table.
Would a JOIN statement be the best option?
Or a sub-query would work better for me to access the data laying on dsb_nb_users table?
This might be an operation i will have to perform a few times so i want to understand the mechanics of it.
INSERT INTO dsb_nb_users_option(dsb_nb_users_option.code, dsb_nb_users_option.code_value, dsb_nb_users_option.status)
SELECT dsb_nb_default_option.code, dsb_nb_default_option.code_value, dsb_nb_default_option.status
FROM dsb_nb_default_options
WHERE dsb_nb_users.user_id IS NOT NULL;
Thank you for your time!!
On the face of it, I see nothing wrong with your query to achieve your goal. That said, I see several things worth pointing out.
First, please learn to format your code - for your own sanity as well as that of others who have to read it. At the very least, put each column name on a line of its own, indented. A good IDE tool like SQL Developer will do this for you. Like this:
INSERT INTO dsb_nb_users_option (
dsb_nb_users_option.code,
dsb_nb_users_option.code_value,
dsb_nb_users_option.status
)
SELECT
dsb_nb_default_option.code,
dsb_nb_default_option.code_value,
dsb_nb_default_option.status
FROM
dsb_nb_default_options
WHERE
dsb_nb_users.user_id IS NOT NULL;
Now that I've made your code more easily readable, a couple of other things jump out at me. First, it is not necessary to prefix every column name with the table name. So your code gets even easier to read.
INSERT INTO dsb_nb_users_option (
code,
code_value,
status
)
SELECT
code,
code_value,
status
FROM
dsb_nb_default_options
WHERE
dsb_nb_users.user_id IS NOT NULL;
Note that there are times you need to qualify a column name, either because oracle requires it to avoid ambiguity to the parser, or because the developer needs it to avoid ambiguity to himself and those that follow. In this case we usually use table name aliasing to shorten the code.
select a.userid,
a.username,
b.user_mobile_phone
from users a,
join user_telephones b on a.userid=b.userid;
Finally, and more critical your your overall design, It appears that you are unnecessarily duplicating data across multiple tables. This goes against all the rules of data design. Have you read up on 'data normalization'? It's the foundation of relational database theory.
Questions have been asked in the past that seems to handle pieces of my full question, but I'm not finding a totally good answer.
Here is the situation:
I'm importing data from an old, but operational and production, Oracle server.
One of the columns is created as LONG RAW.
I will not be able to convert the table to a BLOB.
I would like to use a global temporary table to pull out data each time I call to the server.
This feels like a good answer, from here: How to create a temporary table in Oracle
CREATE GLOBAL TEMPORARY TABLE newtable
ON COMMIT PRESERVE ROWS
AS SELECT
MYID, TO_LOB("LONGRAWDATA") "BLOBDATA"
FROM oldtable WHERE .....;
I do not want the table hanging around, and I'd only do a chunk of rows at a time, to pull out the old table in pieces, each time killing the table. Is it acceptable behavior to do the CREATE, then do the SELECT, then DROP?
Thanks..
--- EDIT ---
Just as a follow up, I decided to take an even different approach to this.
Branching the strong-oracle package, I was able to do what I originally hoped to do, which was to pull the data directly from the table without doing a conversion.
Here is the issue I've posted. If I am allowed to publish my code to a branch, I'll post a follow up here for completeness.
Oracle ODBC Driver Release 11.2.0.1.0 says that Prefetch for LONG RAW data types is supported, which is true.
One caveat is that LONG RAW can technically be up to 2GB in size. I had to set a hard max size of 10MB in the code, which is adequate for my use, so far at least. This probably could be a variable sent in to the connection.
This fix is a bit off original topic now however, but it might be useful to someone else.
With Oracle GTTs, it is not be necessary to drop and create each time, and you don't need to worry about data "hanging around." In fact, it's inadvisable to drop and re-create. The structure itself persists, but the data in it does not. The data only persists within each session. You can test this by opening up two separate clients, loading data with one, and you will notice it's not there in the second client.
In effect, each time you open a session, it's like you are reading a completely different table, which was just truncated.
If you want to empty the table within your stored procedure, you can always truncate it. Within a stored proc, you will need to execute immediate if you do this.
This is really handy, but it also can make debugging a bear if you are implementing GTTs through code.
Out of curiosity, why a chunk at a time and not the entire dataset? What kind of data volumes are you talking about?
-- EDIT --
Per our comments conversation, this is very raw and untested, but I hope it will give you an idea what I mean:
CREATE OR REPLACE PROCEDURE LOAD_DATA()
AS
TOTAL_ROWS number;
TABLE_ROWS number := 1;
ROWS_AT_A_TIME number := 100;
BEGIN
select count (*)
into TOTAL_ROWS
from oldtable;
WHILE TABLE_ROWS <= TOTAL_ROWS
LOOP
execute immediate 'truncate table MY_TEMP_TABLE';
insert into MY_TEMP_TABLE
SELECT
MYID, TO_LOB(LONGRAWDATA) as BLOBDATA
FROM oldtable
WHERE ROWNUM between TABLE_ROWS and TABLE_ROWS + ROWS_AT_A_TIME;
insert into MY_REMOTE_TABLE#MY_REMOTE_SERVER
select * from MY_TEMP_TABLE;
commit;
TABLE_ROWS := TABLE_ROWS + ROWS_AT_A_TIME;
END LOOP;
commit;
end LOAD_DATA;
Lets suppose I created one table--
Create table t1 (aa varchar2(5),bb varchar2(5),cc varchar2(5));
Inserted values in it--
insert into T1 values ('a','b','c');
commit;
Now in one scenario, if i wanted to update all columns with same value then I am doing by this way--
UPDATE T1 SET AA='x',BB='x',CC='x';
Is there any another way by which this update task can be accomplished considering in real time there may be quite large number of columns and all has to be updated with same value in one go?
I am using Oracle 11.2.0.1.0 - 64bit Production
Note: Usually there are very less any scenarios where same values are being updated for all columns. But for example consider a school database and a good student scores 10/10 marks in all subjects. :-)
Thanks.
There is no way to do it in pure SQL. You must list down all the columns explicitly in the UPDATE statement.
And, believe me it is not a difficult task using a good text editor. Using the metadata you could get the list of column names in few seconds, all you need to do is prepare the SQL statement as per the syntax.
If you really want to do it dynamically, then you need to do it in PL/SQL and (ab)use EXECUTE IMMEDIATE. I would personally not suggest it unless you are just doing it for learning purpose.
You could try this:
UPDATE T1 SET AA='x',BB=AA,CC=AA;
I'm using Oracle SQL Developer version 4.02.15.21.
I need to write a query that accesses multiple databases. All that I'm trying to do is get a list of all the IDs present in "TableX" (There is an instance of Table1 in each of these databases, but with different values) in each database and union all of the results together into one big list.
My problem comes with accessing more than 4 databases -- I get this error: ORA-02020: too many database links in use. I cannot change the INIT.ORA file's open_links maximum limit.
So I've tried dynamically opening/closing these links:
SELECT Local.PUID FROM TableX Local
UNION ALL
----
SELECT Xdb1.PUID FROM TableX#db1 Xdb1;
ALTER SESSION CLOSE DATABASE LINK db1
UNION ALL
----
SELECT Xdb2.PUID FROM TableX#db2 Xdb2;
ALTER SESSION CLOSE DATABASE LINK db2
UNION ALL
----
SELECT Xdb3.PUID FROM TableX#db3 Xdb3;
ALTER SESSION CLOSE DATABASE LINK db3
UNION ALL
----
SELECT Xdb4.PUID FROM TableX#db4 Xdb4;
ALTER SESSION CLOSE DATABASE LINK db4
UNION ALL
----
SELECT Xdb5.PUID FROM TableX#db5 Xdb5;
ALTER SESSION CLOSE DATABASE LINK db5
However this produces 'ORA-02081: database link is not open.' On whichever db is being closed out last.
Can someone please suggest an alternative or adjustment to the above?
Please provide a small sample of your suggestion with syntactically correct SQL if possible.
If you can't change the open_links setting, you cannot have a single query that selects from all the databases you want to query.
If your requirement is to query a large number of databases via database links, it seems highly reasonable to change the open_links setting. If you have one set of people telling you that you need to do X (query data from a large number of tables) and another set of people telling you that you cannot do X, it almost always makes sense to have those two sets of people talk and figure out which imperative wins.
If we can solve the problem without writing a single query, then you have options. You can write a bit of PL/SQL, for example, that selects the data from each table in turn and does something with it. Depending on the number of database links involved, it may make sense to write a loop that generates a dynamic SQL statement for each database link, executes the SQL, and then closes the database link.
If you want need to provide a user with the ability to run a single query that returns all the data, you can write a pipelined table function that implements this sort of loop with dynamic SQL and then let the user query the pipelined table function. This isn't really a single query that fetches the data from all the tables. But it is as close as you're likely to get without modifying the open_links limit.
This question already has answers here:
Does Oracle have an equivalent of SQL Server's table variables?
(4 answers)
Closed 8 years ago.
I've recently started a new position as a developer and I'm having a bit of trouble with PL/SQL. I've used MS SQL for a number of years but I'm finding PL/SQL a bit trickier.
One of the things I used to do when writing functions and stored procedures in MS SQL was to put reoccuring result sets into a table variable so I wouldn't have to requery them throughout my procedure.
Something like this:
declare #badPeople table(recordPointer int)
insert into #badPeople
select BP_Record_Pointer
from People
where BP_Bad = 1
I'm looking at doing something similar in PL/SQL but I'm not quite sure how to get started. Any ideas if this is even possible?
declare
type t_number is table of number;
v_numbers t_number;
begin
select BP_Record_Pointer
bulk collect into v_numbers
from People
where BP_Bad = 1;
end;
This will create a nested table containing the values from your table. It's important to note that the table will go out-of-scope at the end of the anonymous block, so anything you want to do with it needs to be done inside that block.
In Oracle unlike MS SQL cursors are not considered the devil and something to avoid. So typically in Oracle you will make use of cursors much more often than you would in MS SQL. Of course if you can do it with only SQL and no cursor that is best, but don't be afraid to test and use cursors in Oracle. Get a good book on PL/SQL, this is a good one http://www.amazon.com/Oracle-PL-SQL-Programming-4th/dp/0596009771. The post by Gratzy is another option you can use. So get a good book that you can use to figure out when to use what. PL/SQL is a very rich environment compared to T-SQL. While it has more of a learning curve once you get over the initial curve it's a really easy and power full language. And on top of that it's a lot of fun.