I have a table that looks like this :
CREATE OR REPLACE TYPE tip_orase AS VARRAY(10) of VARCHAR2(50)
/
CREATE table excursie_try (
cod_excursie NUMBER(4),
denumire VARCHAR2(20),
orase tip_orase,
status varchar2(20)
);
And i need to find out 'cod_excursie' of the entry that has in orase the lowest number of entries.
I can do this with a lot of work by counting for each entry the number of cities and selecting a minimum. Then making a query to give 'cod_excursie' of the entry that has the lowest number of entries in orase.
Is there a simpler way ? I tried something like:
select cod_excursie
from excursie_try, (select max(orase.count()) m
from excursie_try) T
where orase.count = T.m
and ROWNUM <= 1;
but it does not work. Any ideas or i have to take the LONG way ?
Try this:
select cod_excursie from (
select et.cod_excursie,
(select count(*) from table(et.orase)) n
from excursie_try et order by 2 desc
) where rownum = 1;
(select count(*) from table(et.orase)) is a single-row subquery, I used TABLE to emulate sql table on varray.
order by 2 desc in the subquery + where rownum = 1 is used for top-N reporting.
Related
I would like to query an Oracle DB table for the number of rows containing each distinct value in a CLOB column.
This returns all rows containing a value:
select * from mytable where dbms_lob.instr(mycol,'value') > 0;
Using DBMS_LOB, this returns the number of rows containing that value:
select count(*) from mytable where dbms_lob.instr(mycol,'value') > 0;
But is it possible to query for the number of times (rows in which) each distinct value appears?
Depending on what that column really contains, see whether TO_CHAR helps.
SQL> create table mytable (mycol clob);
Table created.
SQL> insert into mytable
2 select 'Query to count distinct values' from dual union all
3 select 'I have no idea which values are popular' from dual;
2 rows created.
SQL> select count(*), to_char(mycol) toc
2 from mytable
3 where dbms_lob.instr(mycol,'value') > 0
4 group by to_char(mycol);
COUNT(*) TOC
---------- ----------------------------------------
1 Query to count distinct values
1 I have no idea which values are popular
SQL>
If your CLOB values are more than 4000 bytes (and if not, why are they CLOBs?) then it's not perfect - collisions are possible, if unlikely - but you could hash the CLOB values.
If you want to count the number of distinct values:
select count(distinct dbms_crypto.hash(src=>mycol, typ=>2))
from mytable
where dbms_lob.instr(mycol,'value') > 0;
If you want to count how many times each distinct value appears:
select mycol, cnt
from (
select mycol,
count(*) over (partition by dbms_crypto.hash(src=>mycol, typ=>2)) as cnt,
row_number() over (partition by dbms_crypto.hash(src=>mycol, typ=>2) order by null) as rn
from mytable
where dbms_lob.instr(mycol,'value') > 0
)
where rn = 1;
Both are likely to be fairly expensive and slow with a lot of data.
(typ=>2 gives the numeric value for dbms_crypto.hash_md5, as you can't refer to the package constant in a SQL call, at least up to 12cR1...)
Rather more crudely, but possibly significantly quicker, you could base the count on the just the first 4000 characters - which may or may not be plausible for your actual data:
select count(distinct dbms_lob.substr(mycol, 4000, 1))
from mytable
where dbms_lob.instr(mycol,'value') > 0;
select dbms_lob.substr(mycol, 4000, 1), count(*)
from mytable
where dbms_lob.instr(mycol,'value') > 0
group by dbms_lob.substr(mycol, 4000, 1);
Standard Oracle functions do not support distinction of CLOB values. But, if you have access to DBMS_CRYPTO.HASH function, you can compare CLOB hashes instead, and thus, get the desired output:
select myCol, h.num from
myTable t join
(select min(rowid) rid, count(rowid) num
from myTable
where dbms_lob.instr(mycol,'value') > 0
group by DBMS_CRYPTO.HASH(myCol, 3)) h
on t.rowid = h.rid;
Also, note, that there's a very little possibility of hash collision. But if that's ok with you, you can use this approach.
select rownum into v_rownum
from waitlist
where p_callnum=callnum
order by sysdate;
tried doing this but gives too many values.
and if I do p_snum=snum, it will keep returning 1. I need it to return 2 if it's #2 on the waitlist.
select rn into v_rownum
from (select callnum,
row_number() over (order by sysdate) rn
from waitlist)
where p_snum=snum;
Almost got it to work. Running into issues in the first select. I believe I might have to use v_count instead. Also Ordering by Sysdate even if a second apart will order it correctly.
SNU CALLNUM TIME
--- ---------- ---------
101 10125 11-DEC-18
103 10125 11-DEC-18
BTW time is = date which I entered people into waitlist using sysdate. So I suppose ordering by time could work.
create table waitlist(
snum varchar2(3),
callnum number(8),
time date,
constraint fk_waitlist_snum foreign key(snum) references students(snum),
constraint fk_waitlist_callnum foreign key(callnum) references schclasses(callnum),
primary key(snum,callnum)
);
is the waitlist table.
I used Scott's DEPT table to create your WAITLIST; department numbers represent CALLNUM column:
SQL> select * From waitlist;
CALLNUM WAITER
---------- --------------------
10 ACCOUNTING
20 RESEARCH
30 SALES
40 OPERATIONS
How to fetch data you need?
using analytic function (ROW_NUMBER) which orders values by CALLNUMs, you'll know the order
that query will be used as an inline view for the main query that returns number in the waitlist for any CALLNUM
Here's how:
SQL> select rn
2 from (select callnum,
3 row_number() over (order by callnum) rn
4 from waitlist
5 )
6 where callnum = 30;
RN
----------
3
SQL>
rownum in oracle is a generated column, it does not refer to any specific row, it is just the nth row in a set.
With a select into it can only return one row (hence the two many rows error) so rownum will always be 1.
Without more details about your table structure, and how you are uniquely identifying records it is hard to give assist you further with a solution.
CREATE OR REPLACE TYPE nvarchar2_list_type AS TABLE OF NVARCHAR2(100);
CREATE TABLE test_table(
id number primary key,
cars_list nvarchar2_list_type
)
NESTED TABLE cars_list STORE AS cars_list_storage_table;
insert into test_table(id, cars_list)
values(1, nvarchar2_list_type( 'AUDI', 'MERCEDES') );
All above operations completed success, 1 rows inserted in table test_table, now i write this function:
create or replace function get_cnt
return number
as
ret_val number;
begin
SELECT cars_list.COUNT
INTO ret_val
from test_table where id = 1;
return ret_val;
end;
This gives error: ORA-00904: "CARS_LIST"."COUNT": invalid identifier
Tell please what is wrong here?
As I know, COUNT method must be used just so (from here)
No, you cannot use count method in this situation. You have SQL nested table at hand, count method is used only with PL/SQL collections.
To count number of nested table's elements you can either unnest that nested table or use scalar sub-query:
Unnesting:
SQL> select id
2 , count(*) as cnt
3 from test_table t
4 cross join table(t.cars_list)
5 group by id
6 ;
ID CNT
---------- ----------
1 2
Scalar sub-query:
SQL> select id
2 , (select count(column_value)
3 from table(t.cars_list)) as cnt
4 from test_table t
5 ;
ID CNT
---------- ----------
1 2
Use
Select
Cardinality(cars_list) from test_table
I can't explain why that doesn't work, but this does:
select (select count(*) from table(cars_list))
into ret_val
from test_table
where id = 1;
Oracle is expecting column name or function in its select list, but what you are giving is collection build in method that operates on collections only.
You can achieve the same using scalar sub query
SELECT (select count(1) from table(cars_list)) as "COUNT"
FROM test_table
WHERE id = 1;
I need to write one procedure to pick the record for given rows
for example
procedure test1
(
start_ind number,
end_ind number,
p_out ref cursor
)
begin
opecn p_out for
select * from test where rownum between start_ind and end_ind;
end;
when we pass start_ind 1 and end_ind 10 its working.But when we change start_ind to 5
then query looks like
select * from test where rownum between 5 and 10;
and its fails and not shows the output.
Please assist how to fix this issue.Thanks!
The rownum is assigned and then the where condition evaluated. Since you'll never have a rownum 1-4 in your result set, you never get to rownum 5. You need something like this:
SELECT * FROM (
SELECT rownum AS rn, t.*
FROM (
SELECT t.*
FROM test t
ORDER BY t.whatever
)
WHERE ROWNUM <= 10
)
WHERE rn >= 5
You'll also want an order by clause in the inner select, or which rows you get will be undefined.
This article by Tom Kyte pretty much tells you everything you need to know: http://www.oracle.com/technetwork/issue-archive/2006/06-sep/o56asktom-086197.html
SELECT *
from (SELECT rownum AS rn, t.*
FROM MyTable t
WHERE ROWNUM <= 10
ORDER BY t.NOT-Whatever
-- (its highly important to use primary or unique key of MyTable)
WHERE rn > 5
As a hint, :
Typically we use store-procedures for data validation, access control, extensive or complex processing that requires execution of several SQL statements. Stored procedures may return result sets, i.e. the results of a SELECT statement. Such result sets can be processed using cursors, by other stored procedures, by associating a result set locator, or by applications
I think you are going to use the ruw-number to fetch paged queries.
Try to create a generic select query based on the idea mentioned above.
Two possibilities:
1) Your table is an index-organized table. So its data is sorted. You would select those first rows you want to avoid and based on that get the next rows you are looking for:
create or replace procedure get_records
(
vi_start_ind integer,
vi_end_ind integer,
vo_cursor out sys_refcursor
) as
begin
open vo_cursor for
select *
from test
where rownum <= vi_end_ind - vi_start_ind + 1
and rowid not in
(
select rowid
from test
where rownum < vi_start_ind
)
;
end;
2) Your table is not index-organized, which is normally the case. Then its records are not sorted. To get records m to n, you would have to tell the system what order you have in mind:
create or replace procedure get_records
(
vi_start_ind number,
vi_end_ind number,
vo_cursor out sys_refcursor
) as
begin
open vo_cursor for
select *
from test
where rownum <= vi_end_ind - vi_start_ind + 1
and rowid not in
(
select rowid from
(
select rowid
from test
order by somthing
)
where rownum < vi_start_ind
)
order by something
;
end;
All this said, think it over what you want to achieve. If you want to use this procedure to read your table block for block, keep in mind that it will read the same data again and again. To know what rows 1,000,001 to 1,000,100 are, the dbms must read through one million rows first.
What is the easiest way to INSERT a row if it doesn't exist, in PL/SQL (oracle)?
I want something like:
IF NOT EXISTS (SELECT * FROM table WHERE name = 'jonny') THEN
INSERT INTO table VALUES ("jonny", null);
END IF;
But it's not working.
Note: this table has 2 fields, say, name and age. But only name is PK.
INSERT INTO table
SELECT 'jonny', NULL
FROM dual -- Not Oracle? No need for dual, drop that line
WHERE NOT EXISTS (SELECT NULL -- canonical way, but you can select
-- anything as EXISTS only checks existence
FROM table
WHERE name = 'jonny'
)
Assuming you are on 10g, you can also use the MERGE statement. This allows you to insert the row if it doesn't exist and ignore the row if it does exist. People tend to think of MERGE when they want to do an "upsert" (INSERT if the row doesn't exist and UPDATE if the row does exist) but the UPDATE part is optional now so it can also be used here.
SQL> create table foo (
2 name varchar2(10) primary key,
3 age number
4 );
Table created.
SQL> ed
Wrote file afiedt.buf
1 merge into foo a
2 using (select 'johnny' name, null age from dual) b
3 on (a.name = b.name)
4 when not matched then
5 insert( name, age)
6* values( b.name, b.age)
SQL> /
1 row merged.
SQL> /
0 rows merged.
SQL> select * from foo;
NAME AGE
---------- ----------
johnny
If name is a PK, then just insert and catch the error. The reason to do this rather than any check is that it will work even with multiple clients inserting at the same time. If you check and then insert, you have to hold a lock during that time, or expect the error anyway.
The code for this would be something like
BEGIN
INSERT INTO table( name, age )
VALUES( 'johnny', null );
EXCEPTION
WHEN dup_val_on_index
THEN
NULL; -- Intentionally ignore duplicates
END;
I found the examples a bit tricky to follow for the situation where you want to ensure a row exists in the destination table (especially when you have two columns as the primary key), but the primary key might not exist there at all so there's nothing to select.
This is what worked for me:
MERGE INTO table1 D
USING (
-- These are the row(s) you want to insert.
SELECT
'val1' AS FIELD_A,
'val2' AS FIELD_B
FROM DUAL
) S ON (
-- This is the criteria to find the above row(s) in the
-- destination table. S refers to the rows in the SELECT
-- statement above, D refers to the destination table.
D.FIELD_A = S.FIELD_A
AND D.FIELD_B = S.FIELD_B
)
-- This is the INSERT statement to run for each row that
-- doesn't exist in the destination table.
WHEN NOT MATCHED THEN INSERT (
FIELD_A,
FIELD_B,
FIELD_C
) VALUES (
S.FIELD_A,
S.FIELD_B,
'val3'
)
The key points are:
The SELECT statement inside the USING block must always return rows. If there are no rows returned from this query, no rows will be inserted or updated. Here I select from DUAL so there will always be exactly one row.
The ON condition is what sets the criteria for matching rows. If ON does not have a match then the INSERT statement is run.
You can also add a WHEN MATCHED THEN UPDATE clause if you want more control over the updates too.
Using parts of #benoit answer, I will use this:
DECLARE
varTmp NUMBER:=0;
BEGIN
-- checks
SELECT nvl((SELECT 1 FROM table WHERE name = 'john'), 0) INTO varTmp FROM dual;
-- insert
IF (varTmp = 1) THEN
INSERT INTO table (john, null)
END IF;
END;
Sorry for I don't use any full given answer, but I need IF check because my code is much more complex than this example table with name and age fields. I need a very clear code. Well thanks, I learned a lot! I'll accept #benoit answer.
In addition to the perfect and valid answers given so far, there is also the ignore_row_on_dupkey_index hint you might want to use:
create table tq84_a (
name varchar2 (20) primary key,
age number
);
insert /*+ ignore_row_on_dupkey_index(tq84_a(name)) */ into tq84_a values ('Johnny', 77);
insert /*+ ignore_row_on_dupkey_index(tq84_a(name)) */ into tq84_a values ('Pete' , 28);
insert /*+ ignore_row_on_dupkey_index(tq84_a(name)) */ into tq84_a values ('Sue' , 35);
insert /*+ ignore_row_on_dupkey_index(tq84_a(name)) */ into tq84_a values ('Johnny', null);
select * from tq84_a;
The hint is described on Tahiti.
you can use this syntax:
INSERT INTO table_name ( name, age )
select 'jonny', 18 from dual
where not exists(select 1 from table_name where name = 'jonny');
if its open an pop for asking as "enter substitution variable" then use this before the above queries:
set define off;
INSERT INTO table_name ( name, age )
select 'jonny', 18 from dual
where not exists(select 1 from table_name where name = 'jonny');
You should use Merge:
For example:
MERGE INTO employees e
USING (SELECT * FROM hr_records WHERE start_date > ADD_MONTHS(SYSDATE, -1)) h
ON (e.id = h.emp_id)
WHEN MATCHED THEN
UPDATE SET e.address = h.address
WHEN NOT MATCHED THEN
INSERT (id, address)
VALUES (h.emp_id, h.address);
or
MERGE INTO employees e
USING hr_records h
ON (e.id = h.emp_id)
WHEN MATCHED THEN
UPDATE SET e.address = h.address
WHEN NOT MATCHED THEN
INSERT (id, address)
VALUES (h.emp_id, h.address);
https://oracle-base.com/articles/9i/merge-statement
CTE and only CTE :-)
just throw out extra stuff. Here is almost complete and verbose form for all cases of life. And you can use any concise form.
INSERT INTO reports r
(r.id, r.name, r.key, r.param)
--
-- Invoke this script from "WITH" to the end (";")
-- to debug and see prepared values.
WITH
-- Some new data to add.
newData AS(
SELECT 'Name 1' name, 'key_new_1' key FROM DUAL
UNION SELECT 'Name 2' NAME, 'key_new_2' key FROM DUAL
UNION SELECT 'Name 3' NAME, 'key_new_3' key FROM DUAL
),
-- Any single row for copying with each new row from "newData",
-- if you will of course.
copyData AS(
SELECT r.*
FROM reports r
WHERE r.key = 'key_existing'
-- ! Prevent more than one row to return.
AND FALSE -- do something here for than!
),
-- Last used ID from the "reports" table (it depends on your case).
-- (not going to work with concurrent transactions)
maxId AS (SELECT MAX(id) AS id FROM reports),
--
-- Some construction of all data for insertion.
SELECT maxId.id + ROWNUM, newData.name, newData.key, copyData.param
FROM copyData
-- matrix multiplication :)
-- (or a recursion if you're imperative coder)
CROSS JOIN newData
CROSS JOIN maxId
--
-- Let's prevent re-insertion.
WHERE NOT EXISTS (
SELECT 1 FROM reports rs
WHERE rs.name IN(
SELECT name FROM newData
));
I call it "IF NOT EXISTS" on steroids. So, this helps me and I mostly do so.