SELECT C1,C2,C3 FROM Tbl
ORDER BY
IF (VariableA > VariableB , C1 DESC , C1 ASC);
Here VariableA and VariableB are the variables declared in
Stored procedure
How could I do this?
This might help -
SELECT C1,C2,C3 FROM Tbl
ORDER BY
CASE WHEN VariableA > VariableB THEN C1 END DESC ,
CASE WHEN VariableA <= VariableB THEN C1 END ASC;
It should be noted that we don't include an ELSE for each CASE, which means any other value will return NULL and be discarded from the ORDER BY.
Related
I'm currently migrating data from legacy system to the current system.
I have this INSERT statement inside a stored procedure.
INSERT INTO TABLE_1
(PRIMARY_ID, SEQUENCE_ID, DESCR)
SELECT LEGACY_ID PRIMARY_ID
, (SELECT COUNT(*) + 1
FROM TABLE_1 T1
WHERE T1.PRIMARY_ID = L1.LEGACY_ID) SEQUENCE_ID
, L1.DESCR
FROM LEGACY_TABLE L1;
However, whenever I have multiple values of LEGACY_ID from LEGACY_TABLE, the query for the SEQUENCE_ID doesn't increment.
Why is this so? I can't seem to find any documentation on how the INSERT INTO SELECT statement works behind the scenes. I am guessing that it selects all the values from the table you are selecting and then inserts them simultaneously after, that's why it doesn't increment the COUNT(*) value?
What other workarounds can I do? I cannot create a SEQUENCE because the SEQUENCE_ID must be based on the number of PRIMARY_ID that are present. They are both primary ids.
Thanks in advance.
Yes, The SELECT will be executed FIRST and only then the INSERT happens.
A Simple PL/SQL block below, will be a simpler approach, though not efficient.
DECLARE
V_SEQUENCE_ID NUMBER;
V_COMMIT_LIMIT:= 20000;
V_ITEM_COUNT := 0;
BEGIN
FOR REC IN (SELECT LEGACY_ID,DESCR FROM LEGACY_TABLE)
LOOP
V_SEQUENCE_ID:= 0;
SELECT COUNT(*)+1 INTO V_SEQUENCE_ID FROM TABLE_1 T1
WHERE T1.PRIMARY_ID = REC.LEGACY_ID
INSERT INTO TABLE_1
(PRIMARY_ID, SEQUENCE_ID, DESCR)
VALUES
(REC.LEGACY_ID,V_SEQUENCE_ID,REC.DESCR);
V_ITEM_COUNT := V_ITEM_COUNT + 1;
IF(V_ITEM_COUNT >= V_COMMIT_LIMIT)
THEN
COMMIT;
V_ITEM_COUNT := 0;
END IF;
END LOOP;
COMMIT;
END;
/
EDIT: Using CTE:
WITH TABLE_1_PRIM_CT(PRIMARY_ID, SEQUENCE_ID) AS
(
SELECT L1.LEGACY_ID,COUNT(*)
FROM LEGACY_TABLE L1
LEFT OUTER JOIN TABLE_1 T1
ON(L1.LEGACY_ID = T1.PRIMARY_ID)
GROUP BY L1.LEGACY_ID
)
INSERT INTO TABLE_1
(SELECT L1.LEGACY_ID,
CTE.SEQUENCE_ID+ (ROW_NUMBER() OVER (PARTITION BY L1.LEGACY_ID ORDER BY null)),
L1.DESCR
FROM TABLE_1_PRIM_CT CTE, LEGACY_TABLE L1
WHERE L1.LEGACY_ID = CTE.PRIMARY_ID);
PS: With your Millions of Rows, this is going to create a temp table
of same size, during execution. Do Explain Plan before actual execution.
I want to write a SQK script with insert query in Oracle where one of the value will be fetched from cursor and rest all will be retrieved from table.
For example, consider Employee table:
Emp_No | Emp_Name
1 | AAA
...........
I am reading the table into a cursor.
Cursor c1 is select emp_no, emp_name from employee;
I am iterating the cursor and adding to a table along with information from another table.
for empCur in c1
loop
insert into employee_info(emp_no, emp_name, address, age, ... ) values (empCur.emp_no, empCur.emp_name, select t.address, t.age, ... from employee_temp_table t where t.emp_no=empCur.emp_no)
end loop;
Is my script valid? If not is there any other way to achieve it? Since few values are in cursor and few are in another table I am not sure how to handle this.
Your script isn't correct because this
select t.address, t.age, ... from employee_temp_table t where t.emp_no=empCur.emp_no
is not a valid expression. You may use a scalar subquery (one-row, one-column subquery) only, like this:
insert into t1(col1, col2, col3) values (1, (select col1 from t2), (select col2 from t2));
Or you may try insert from select:
for empCur in c1 loop
insert into employee_info(emp_no, emp_name, address, age, ... )
select empCur.emp_no, empCur.emp_name, t.address, t.age, ... from employee_temp_table t where t.emp_no=empCur.emp_no;
end loop;
If you want to use the cursor, why not just join the tables inside the cursor?
for empCur in ( select e.emp_no, e.emp_name, t.address, t.age ...
from employee e join employee_temp_table t on ( t.emp_no = e.emp_no )
) loop
insert into employee_info(...) values ( empCur.emp_no, ...);
end loop;
Or with a sql insert: (if you can choose sql over pl/sql - T Kyte says do it)
insert into employee_info
select e.emp_no, e.emp_name, t.address, t.age ...
from employee e join employee_temp_table t on ( t.emp_no = e.emp_no );
I was wondering if the following code is a good practice
CURSOR c_price_hist_parent IS
select tran_type, reason, event,
unit_cost, unit_retail, selling_unit_retail,
selling_uom, multi_units, multi_unit_retail,
multi_selling_uom
from price_hist
where rowid = ( SELECT row_id
from ( SELECT rowid row_id
FROM price_hist
WHERE item = l_item_parent
and tran_type in (4,8)
and loc = l_location
and ACTION_DATE <= l_create_date
order by action_date desc
)
where rownum = 1
);
If we delete a row and then insert the same row all the columns remain same but the rowid doesn't, so in this case it will not match. Please let me know your thoughts.
As mentioned before, using rownum can be tricky, because inserts or deletes can happen at the same time which could change rownums.
If I understand your query correctly, you are simply trying to get the record with the latest action_date. Why not do the following:
CURSOR c_price_hist_parent IS
select sub.tran_type, sub.reason, sub.event,
sub.unit_cost, sub.unit_retail, sub.selling_unit_retail,
sub.selling_uom, sub.multi_units, sub.multi_unit_retail,
sub.multi_selling_uom
from (
select *
from price_hist
where item = l_item_parent
and tran_type in (4,8)
and loc = l_location
and ACTION_DATE <= l_create_date
order by action_date desc
) sub
where rownum = 1
);
I have sql like below inside a Multi-Step Table valued function..I have shortened the query a bit to make it easy to understand.
CREATE FUNCTION [dbo].[fn_ph]
(
-- Add the parameters for the function here
#pAsOfDate date,
#pAccountId nvarchar(15)
)
RETURNS #HH TABLE
(
-- Add the column definitions for the TABLE variable here
AsOfDate date,
AccountId nvarchar(15),
LongName varchar(100),
ShortName varchar(100)
)
AS
BEGIN
declare #longOrShortIndicator int
select #longOrShortIndicator = COUNT(distinct LongOrShortIndicator) from table1 a
select a.*,
case
when a.SecType='CASH' and #longOrShortIndicator > 1 then 'C'
else a.LongOrShortIndicator
end as LongOrShortIndicator
from Table1 a
END
The expression when a.SecType='CASH' and #longOrShortIndicator > 1 then 'C' is the bottleneck.
if i remove the #longOrShortIndicator > 1 the query runs fast
If i run the query outside of the function it returns fast...
Why is the local variable slowing down the entire query? Any help would be appreciated.
thanks
The listing does not show what you want to do with #HH, your return table, but in #longOrShortIndicator you are obviously counting rows in table1. If you're doing it many times, e.g. for all rows of your return table, then it is slow indeed, it would be slow even on the death star.
Guessing here: maybe you could try moving the #LongOrShortIndicator variable out of the query and into an IF statement:
declare #longOrShortIndicator int
select #longOrShortIndicator = COUNT(distinct LongOrShortIndicator) from table1 a
IF #longOrShortIndicator > 1 BEGIN
select a.*,
CASE when a.SecType='CASH' then 'C'
else a.LongOrShortIndicator
end as LongOrShortIndicator
from Table1 a
END ELSE BEGIN
select a.*, a.LongOrShortIndicator
from Table1 a
END
Is there a way to make selecting random rows faster in oracle with a table that has million of rows. I tried to use sample(x) and dbms_random.value and its taking a long time to run.
Thanks!
Using appropriate values of sample(x) is the fastest way you can. It's block-random and row-random within blocks, so if you only want one random row:
select dbms_rowid.rowid_relative_fno(rowid) as fileno,
dbms_rowid.rowid_block_number(rowid) as blockno,
dbms_rowid.rowid_row_number(rowid) as offset
from (select rowid from [my_big_table] sample (.01))
where rownum = 1
I'm using a subpartitioned table, and I'm getting pretty good randomness even grabbing multiple rows:
select dbms_rowid.rowid_relative_fno(rowid) as fileno,
dbms_rowid.rowid_block_number(rowid) as blockno,
dbms_rowid.rowid_row_number(rowid) as offset
from (select rowid from [my_big_table] sample (.01))
where rownum <= 5
FILENO BLOCKNO OFFSET
---------- ---------- ----------
152 2454936 11
152 2463140 32
152 2335208 2
152 2429207 23
152 2746125 28
I suspect you should probably tune your SAMPLE clause to use an appropriate sample size for what you're fetching.
Start with Adam's answer first, but if SAMPLE just isn't fast enough, even with the ROWNUM optimization, you can use block samples:
....FROM [table] SAMPLE BLOCK (0.01)
This applies the sampling at the block level instead of for each row. This does mean that it can skip large swathes of data from the table so the sample percent will be very rough. It's not unusual for a SAMPLE BLOCK with a low percentage to return zero rows.
Here's the same question on AskTom:
http://asktom.oracle.com/pls/apex/f?p=100:11:0::::P11_QUESTION_ID:6075151195522
If you know how big your table is, use sample block as described above. If you don't, you can modify the routine below to get however many rows you want.
Copied from: http://asktom.oracle.com/pls/apex/f?p=100:11:0::::P11_QUESTION_ID:6075151195522#56174726207861
create or replace function get_random_rowid
( table_name varchar2
) return urowid
as
sql_v varchar2(100);
urowid_t dbms_sql.urowid_table;
cursor_v integer;
status_v integer;
rows_v integer;
begin
for exp_v in -6..2 loop
exit when (urowid_t.count > 0);
if (exp_v < 2) then
sql_v := 'select rowid from ' || table_name
|| ' sample block (' || power(10, exp_v) || ')';
else
sql_v := 'select rowid from ' || table_name;
end if;
cursor_v := dbms_sql.open_cursor;
dbms_sql.parse(cursor_v, sql_v, dbms_sql.native);
dbms_sql.define_array(cursor_v, 1, urowid_t, 100, 0);
status_v := dbms_sql.execute(cursor_v);
loop
rows_v := dbms_sql.fetch_rows(cursor_v);
dbms_sql.column_value(cursor_v, 1, urowid_t);
exit when rows_v != 100;
end loop;
dbms_sql.close_cursor(cursor_v);
end loop;
if (urowid_t.count > 0) then
return urowid_t(trunc(dbms_random.value(0, urowid_t.count)));
end if;
return null;
exception when others then
if (dbms_sql.is_open(cursor_v)) then
dbms_sql.close_cursor(cursor_v);
end if;
raise;
end;
/
show errors
Below Solution to this question is not the exact answer but in many scenarios you try to select a row and try to use it for some purpose and then update its status with "used" or "done" so that you do not select it again.
Solution:
Below query is useful but that way if your table is large, I just tried and see that you definitely face performance problem with this query.
SELECT * FROM
( SELECT * FROM table
ORDER BY dbms_random.value )
WHERE rownum = 1
So if you set a rownum like below then you can work around the performance problem. By incrementing rownum you can reduce the possiblities. But in this case you will always get rows from the same 1000 rows. If you get a row from 1000 and update its status with "USED", you will almost get different row everytime you query with "ACTIVE"
SELECT * FROM
( SELECT * FROM table
where rownum < 1000
and status = 'ACTIVE'
ORDER BY dbms_random.value )
WHERE rownum = 1
update the rows status after selecting it, If you can not update that means another transaction has already used it. Then You should try to get a new row and update its status. By the way, getting the same row by two different transaction possibility is 0.001 since rownum is 1000.
Someone told sample(x) is the fastest way you can.
But for me this method works slightly faster than sample(x) method.
It should take fraction of the second (0.2 in my case) no matter what is the size of the table. If it takes longer try to use hints (--+ leading(e) use_nl(e t) rowid(t)) can help
SELECT *
FROM My_User.My_Table
WHERE ROWID = (SELECT MAX(t.ROWID) KEEP(DENSE_RANK FIRST ORDER BY dbms_random.value)
FROM (SELECT o.Data_Object_Id,
e.Relative_Fno,
e.Block_Id + TRUNC(Dbms_Random.Value(0, e.Blocks)) AS Block_Id
FROM Dba_Extents e
JOIN Dba_Objects o ON o.Owner = e.Owner AND o.Object_Type = e.Segment_Type AND o.Object_Name = e.Segment_Name
WHERE e.Segment_Name = 'MY_TABLE'
AND(e.Segment_Type, e.Owner, e.Extent_Id) =
(SELECT MAX(e.Segment_Type) AS Segment_Type,
MAX(e.Owner) AS Owner,
MAX(e.Extent_Id) KEEP(DENSE_RANK FIRST ORDER BY Dbms_Random.Value) AS Extent_Id
FROM Dba_Extents e
WHERE e.Segment_Name = 'MY_TABLE'
AND e.Owner = 'MY_USER'
AND e.Segment_Type = 'TABLE')) e
JOIN My_User.My_Table t
ON t.Rowid BETWEEN Dbms_Rowid.Rowid_Create(1, Data_Object_Id, Relative_Fno, Block_Id, 0)
AND Dbms_Rowid.Rowid_Create(1, Data_Object_Id, Relative_Fno, Block_Id, 32767))
Version with retries when no rows returned:
WITH gen AS ((SELECT --+ inline leading(e) use_nl(e t) rowid(t)
MAX(t.ROWID) KEEP(DENSE_RANK FIRST ORDER BY dbms_random.value) Row_Id
FROM (SELECT o.Data_Object_Id,
e.Relative_Fno,
e.Block_Id + TRUNC(Dbms_Random.Value(0, e.Blocks)) AS Block_Id
FROM Dba_Extents e
JOIN Dba_Objects o ON o.Owner = e.Owner AND o.Object_Type = e.Segment_Type AND o.Object_Name = e.Segment_Name
WHERE e.Segment_Name = 'MY_TABLE'
AND(e.Segment_Type, e.Owner, e.Extent_Id) =
(SELECT MAX(e.Segment_Type) AS Segment_Type,
MAX(e.Owner) AS Owner,
MAX(e.Extent_Id) KEEP(DENSE_RANK FIRST ORDER BY Dbms_Random.Value) AS Extent_Id
FROM Dba_Extents e
WHERE e.Segment_Name = 'MY_TABLE'
AND e.Owner = 'MY_USER'
AND e.Segment_Type = 'TABLE')) e
JOIN MY_USER.MY_TABLE t ON t.ROWID BETWEEN Dbms_Rowid.Rowid_Create(1, Data_Object_Id, Relative_Fno, Block_Id, 0)
AND Dbms_Rowid.Rowid_Create(1, Data_Object_Id, Relative_Fno, Block_Id, 32767))),
Retries(Cnt, Row_Id) AS (SELECT 1, gen.Row_Id
FROM Dual
LEFT JOIN gen ON 1=1
UNION ALL
SELECT Cnt + 1, gen.Row_Id
FROM Retries
LEFT JOIN gen ON 1=1
WHERE Retries.Row_Id IS NULL AND Retries.Cnt < 10)
SELECT *
FROM MY_USER.MY_TABLE
WHERE ROWID = (SELECT Row_Id
FROM Retries
WHERE Row_Id IS NOT NULL)
Can you use pseudorandom rows?
select * from (
select * from ... where... order by ora_hash(rowid)
) where rownum<100