How to create a temporary table in oracle without knowing the number and name of columns.
For example:
Select columnA,columnB,* into temp_table from tableA.
Here,tableA maynot be a simple tablename but maybe derived from many queries.
How can this be achieved?Is there any alternative to this?
In Oracle, you have to first create a table, then insert into it. Or, create it directly (as in my example).
Note that I've created a "normal" table; if it were temporary, you could have chosen between a global or private (depending on database version you use).
For this discussion, I guess that it is just fine:
SQL> create table temp_table as
2 select a.*
3 from (select d.deptno, d.dname, e.ename --> this SELECT is your "tableA"
4 from emp e join dept d
5 on e.deptno = d.deptno
6 where job = 'CLERK'
7 ) a;
Table created.
SQL> select * from temp_table;
DEPTNO DNAME ENAME
---------- -------------------- ----------
10 ACCOUNTING MILLER
20 RESEARCH SMITH
20 RESEARCH ADAMS
30 SALES JAMES
SQL>
Alternatively, create a view and work with it:
SQL> create or replace view v_temp as
2 select d.deptno, d.dname, e.ename
3 from emp e join dept d
4 on e.deptno = d.deptno
5 where job = 'CLERK'
6 ;
View created.
SQL> select * from v_temp;
DEPTNO DNAME ENAME
---------- -------------------- ----------
10 ACCOUNTING MILLER
20 RESEARCH SMITH
20 RESEARCH ADAMS
30 SALES JAMES
SQL>
This statement creates temp_table which contains all columns and data from tableA and two other empty columns, varchar and numeric.
create table temp_table as
select cast (null as varchar2(10)) columnA,
cast (null as number(6)) columnB,
tableA.*
from tableA
If you need only structure, no data, then add:
where 1 = 0
I am not sure why you want to have a temp table as you do not know columns, but you can think of dynamic SQL to create table depending on columns required during your process and then drop it again. From my point of view I think it is not a good design.
I can suggest to think on using collection with 'x' number of columns with datatype as VARCHAR2. During transaction you can populate and process according to you need and it will also remain for that session.
Related
I would like to compare two SQL statements which produce the same result. For example
SELECT
id, name,
(SELECT street || ' ' || town from addresses WHERE addresses.id=customers.addressid) AS address
FROM customers;
-- vs
SELECT
id, name,
street || ' ' || town AS address
FROM customers c LEFT JOIN addresses a ON c.id=a.customerid;
Here I want to compare the performance of the subquery compared to using a join. I know about the other advantages and disadvantages of subqueries and joins, but I’m more interested in comparing their performance.
How can I do a performance comparison? Is there some sort of timing test?
Is there some sort of timing test?
Yes, in SQL*Plus, do it as
SQL> set timing on
and then run queries, each of them several times (to avoid caching issues) and compare time needed for each query to complete. Note that on small data sets you won't notice any difference, so - whichever you use, it'll be OK.
SQL> select e.deptno, (select d.dname from dept d where d.deptno = e.deptno) dname, e.ename
2 from emp e
3 where e.deptno = 20;
DEPTNO DNAME ENAME
---------- -------------- ----------
20 RESEARCH SMITH
20 RESEARCH JONES
20 RESEARCH SCOTT
20 RESEARCH ADAMS
20 RESEARCH FORD
Elapsed: 00:00:00.04
SQL> select e.deptno, d.dname, e.ename
2 from emp e join dept d on e.deptno = d.deptno
3 where e.deptno = 20;
DEPTNO DNAME ENAME
---------- -------------- ----------
20 RESEARCH SMITH
20 RESEARCH JONES
20 RESEARCH SCOTT
20 RESEARCH ADAMS
20 RESEARCH FORD
Elapsed: 00:00:00.03
SQL>
Other than that, did you compare explain plans? Did you collect statistics on tables and indexes (and do it regularly)? Are there any indexes (should be on columns used in joins, most probably)?
So i am trying to update my Vorschlagspakete table with some values i got from other tables. Precisely there are 3 values i want to write into the main table. Atm it looks like this:
update vorschlagspakete
set (paketid, verkaufsstelleid) = (
select k.paketid, k.verkaufsstelleid
from Konfiguration k, bewertung b
where k.konfigurationsid = b.konfigurationsid
group by k.paketid, k.verkaufsstelleid
having avg(b.sterne) >= 5);
But every time i tried this it results into ora-01427.
Error you got, ORA-01427, means too many rows (were returned by subquery). For example based on Scott's schema (as I don't have your tables), it looks like this:
SQL> update emp e set
2 (e.ename, e.job) = (select d.dname, d.loc from dept d);
(e.ename, e.job) = (select d.dname, d.loc from dept d)
*
ERROR at line 2:
ORA-01427: single-row subquery returns more than one row
Why wouldn't it work? Because subquery returns more than a single row!
SQL> select d.dname, d.loc from dept d;
DNAME LOC
-------------- -------------
ACCOUNTING NEW YORK
RESEARCH DALLAS
SALES CHICAGO
OPERATIONS BOSTON
SQL>
So, how would you put all those values into a single row of the EMP table? That won't work, obviously, so you have to do something to restrict number of rows. How? Well, it depends.
sometimes DISTINCT helps, e.g.
select distinct d.dname, d.loc from dept d
sometimes additional WHERE condition helps, e.g.
select d.dname, d.loc from dept d
where d.location = 'NEW YORK'
sometimes joining with the table to be updated helps, e.g.
select d.dname, d.loc from dept d where d.deptno = e.deptno
which leads to
SQL> update emp e set
2 (e.ename, e.job) = (select d.dname, d.loc from dept d where d.deptno = e.deptno);
14 rows updated.
What should you do? I don't know, we don't have your data. See whether something written above helps.
The situation is that, when I import a file into the database, one of the first thing I usually do is to assign an unique ID for each record.
I normally do below in TSQL
ALTER TABLE MyTable
ADD ID INT IDENTITY(1,1)
I am wondering if there is something similar in PL SQL?
All my search result come back with multiple steps.
Then I'd like to know what PL SQL programmer typically do to ID records after importing a file. Do they do that?
The main purpose for me to ID these records is to trace it back after manipulation/copying.
Again, I understand there is solution there, my further question is whether PL SQL programmer actually do that, or there is other alternative which making this step not necessary in PL SQL?
OK then, as you're on Oracle 11g, there's no identity column there so - back to multiple steps. Here's an example:
I'm creating a table that simulates your imported table:
SQL> create table tab_import as
2 select ename, job, sal
3 from emp
4 where deptno = 10;
Table created.
Add the ID column:
SQL> alter table tab_import add id number;
Table altered.
Create a sequence which will be used to populate the ID column:
SQL> create sequence seq_imp;
Sequence created.
Update current rows:
SQL> update tab_import set
2 id = seq_imp.nextval;
3 rows updated.
Create a trigger which will take care about future inserts (if any):
SQL> create or replace trigger trg_bi_imp
2 before insert on tab_import
3 for each row
4 begin
5 :new.id := seq_imp.nextval;
6 end;
7 /
Trigger created.
Check what's in the table at the moment:
SQL> select * from tab_import;
ENAME JOB SAL ID
---------- --------- ---------- ----------
CLARK MANAGER 2450 1
KING PRESIDENT 5000 2
MILLER CLERK 1300 3
Let's import some more rows:
SQL> insert into tab_import (ename, job, sal)
2 select ename, job, sal
3 from emp
4 where deptno = 20;
3 rows created.
The trigger had silently populated the ID column:
SQL> select * From tab_import;
ENAME JOB SAL ID
---------- --------- ---------- ----------
CLARK MANAGER 2450 1
KING PRESIDENT 5000 2
MILLER CLERK 1300 3
SMITH CLERK 800 4
JONES MANAGER 2975 5
FORD ANALYST 3000 6
6 rows selected.
SQL>
Shortly: you need to
alter table and add the ID column
create a sequence
create a trigger
The end.
The answer given by #Littlefoot would be my recommendation too - but still I thought I could mention the following variant which will work only if you do not intend to add more rows to the table later.
ALTER TABLE MyTable add id number(38,0);
update MyTable set id = rownum;
commit;
My test:
SQL> create table tst as select * from all_tables;
Table created.
SQL> alter table tst add id number(38,0);
Table altered.
SQL> update tst set id = rownum;
3815 rows updated.
SQL> alter table tst add constraint tstPk primary key (id);
Table altered.
SQL>
SQL> select id from tst where id < 15;
ID
----------
1
2
3
4
5
6
7
8
9
10
11
ID
----------
12
13
14
14 rows selected.
But as mentioned initially,- this only fixes numbering for the rows you have at the time of the update - your'e not going to get new id values for new rows anytime later - if you need that, go for the sequence solution.
You can add an id column to a table with a single statement (Oracle 11g, see dbfiddle):
alter table test_
add id raw( 16 ) default sys_guid() ;
Example:
-- create a table without an id column
create table test_ ( str )
as
select dbms_random.string( 'x', 16 )
from dual
connect by level <= 10 ;
select * from test_ ;
STR
ULWL9EXFG6CIO72Z
QOM0W1R9IJ2ZD3DW
YQWAP4HZNQ57C2UH
EETF2AXD4ZKNIBBF
W9SECJYDER793MQW
alter table test_
add id raw( 16 ) default sys_guid() ;
select * from test_ ;
STR ID
ULWL9EXFG6CIO72Z 0x782C6EBCAE2D7B9FE050A00A02005D65
QOM0W1R9IJ2ZD3DW 0x782C6EBCAE2E7B9FE050A00A02005D65
YQWAP4HZNQ57C2UH 0x782C6EBCAE2F7B9FE050A00A02005D65
EETF2AXD4ZKNIBBF 0x782C6EBCAE307B9FE050A00A02005D65
W9SECJYDER793MQW 0x782C6EBCAE317B9FE050A00A02005D65
Testing
-- Are the id values unique and not null? Yes.
alter table test_
add constraint pkey_test_ primary key ( id ) ;
-- When we insert more rows, will the id be generated? Yes.
begin
for i in 1 .. 100
loop
insert into test_ (str) values ( 'str' || to_char( i ) ) ;
end loop ;
end ;
/
select * from test_ order by id desc ;
-- last 10 rows of the result
STR ID
str100 0x782C806E16A5E998E050A00A02005D81
str99 0x782C806E16A4E998E050A00A02005D81
str98 0x782C806E16A3E998E050A00A02005D81
str97 0x782C806E16A2E998E050A00A02005D81
str96 0x782C806E16A1E998E050A00A02005D81
str95 0x782C806E16A0E998E050A00A02005D81
str94 0x782C806E169FE998E050A00A02005D81
str93 0x782C806E169EE998E050A00A02005D81
str92 0x782C806E169DE998E050A00A02005D81
str91 0x782C806E169CE998E050A00A02005D81
Regarding your other questions:
{1} Then I'd like to know what PL SQL programmer typically do to ID records after importing a file. Do they do that? The main purpose for me to ID these records is to trace it back after manipulation/copying.
-> As you know, the purpose of an id is: to identify a row. We don't "do anything to IDs". Thus, your usage of IDs seems legit.
{2} Again, I understand there is solution there, my further question is whether PL SQL programmer actually do that, or there is other alternative which making this step not necessary in PL SQL?
-> Not quite sure what you are asking here. Although there is a ROWID() pseudocolumn (see documentation), we should not use it to identify rows.
"You should not use ROWID as the primary key of a table. If you delete
and reinsert a row with the Import and Export utilities, for example,
then its rowid may change. If you delete a row, then Oracle may
reassign its rowid to a new row inserted later."
I have used mysql database in my application, but I want to migrate to Oracle.
The problem is in that query:
select * from users limit ?,1;"
That query returns every row one by one depending on ?.
How can i do that in oracle?
On Oracle 12c, you could use the row limiting feature using FETCH FIRST clause.
SQL> SELECT empno, sal, deptno FROM emp ORDER BY empno DESC
2 FETCH FIRST 1 ROWS ONLY;
EMPNO SAL DEPTNO
---------- ---------- ----------
7934 1300 10
SQL>
Prior 12c solution is ROWNUM, however, if you want the row to be first sorted, then you need to do it in a sub-query -
SQL> SELECT empno, sal, deptno FROM
2 ( SELECT * FROM emp ORDER BY empno DESC
3 ) WHERE ROWNUM = 1;
EMPNO SAL DEPTNO
---------- ---------- ----------
7934 1300 10
SQL>
If the order doesn't matter to you, if you just want any random row, simply use ROWNUM.
Depending on your requirement, you could also use ANALYTIC functions such as ROW_NUMBER, RANK, DENSE_RANK.
select * from (select rownum r, u.* from users u ) where r=1;
or if you want it sorted (replace x by columnnumber or columnname):
select * from (select rownum r, u.* from users u order by x) where r=1;
I was given a query to explain. Could someone please explain it to me:
select j.ip_num from
jobs j, address a
where j.jobtype='C' and
a.sel_code(+)='H' and
j.ip_num=a.ip_num and
a.ip_num is null order by a.ip_num
That query selects every JOB.IP_NUM which doesn't have a matching ADDRESS record or where the matching ADDRESS record has a SEL_CODE not equal to 'H'.
The (+) is Oracle's old outer join syntax. It is the only OUTER JOIN syntax supported in versions of Oracle before 9i.
In this query we get one row for every row in EMP which matches a department, plus a row for the DEPTNO=40, which has no employees:
SQL> select d.dname
2 , e.ename
3 from dept d
4 , emp e
5 where d.deptno = e.deptno(+)
6 /
DNAME ENAME
-------------- ----------
ACCOUNTING SCHNEIDER
ACCOUNTING BOEHMER
ACCOUNTING KISHORE
RESEARCH ROBERTSON
RESEARCH KULASH
RESEARCH GASPAROTTO
RESEARCH RIGBY
RESEARCH CLARKE
SALES HALL
SALES CAVE
SALES SPENCER
SALES BILLINGTON
SALES PADFIELD
SALES VAN WIJK
SALES KESTELYN
SALES LIRA
OPERATIONS PSMITH
HOUSEKEEPING VERREYNNE
HOUSEKEEPING FEUERSTEIN
HOUSEKEEPING PODER
HOUSEKEEPING TRICHLER
COMMUNICATIONS
22 rows selected.
SQL>
Now, if we put an additional filter on the EMP table like this, we simply get one record for each Department, because only one record in EMP now matches:
SQL> select d.dname
2 , e.ename
3 from dept d
4 , emp e
5 where d.deptno = e.deptno(+)
6 and e.ename(+) = 'CAVE'
7 /
DNAME ENAME
-------------- ----------
ACCOUNTING
RESEARCH
SALES CAVE
OPERATIONS
HOUSEKEEPING
COMMUNICATIONS
6 rows selected.
SQL>
/
To convert this query into the ANSI SQL syntax we have to do this:
SQL> select d.dname
2 , e.ename
3 from dept d
4 left outer join emp e
5 on ( d.deptno = e.deptno
6 and e.ename = 'CAVE' )
7 /
DNAME ENAME
-------------- ----------
ACCOUNTING
RESEARCH
SALES CAVE
OPERATIONS
HOUSEKEEPING
COMMUNICATIONS
6 rows selected.
SQL>
Note that if we don't include the additonal clause in the JOIN but leave it in the WHERE clause we get a different result:
SQL> select d.dname
2 , e.ename
3 from dept d
4 left outer join emp e
5 on ( d.deptno = e.deptno )
6 where e.ename = 'CAVE'
7 /
DNAME ENAME
-------------- ----------
SALES CAVE
SQL>
This is the equivalent of omitting the (+) in the second old skool query.
The query is joining the 2 tables jobs, and address. These tables are joining on the field ip_num but you are looking for the records that exist in the jobs table but do not exist in the address table.
This is a LEFT OUTER JOIN. This query could also be written
SELECT j.ip_num
FROM jobs j
LEFT OUTER JOIN address a
ON j.ip_num=a.ip_num
WHERE j.jobtype='C' AND
a.sel_code(+)='H' AND
a.ip_num is null
ORDER BY a.ip_num
It might be useful to see a visual picture joins http://www.codinghorror.com/blog/2007/10/a-visual-explanation-of-sql-joins.html