I have the following MERGE statement.Is there a way to convert this into an update statement without using MERGE?
MERGE INTO tab1
USING (SELECT tab1.col1, tab2.col2
FROM tab1, tab2
WHERE tab1.col1 = tab2.col1) tab3
ON (tab1.col1 = tab3.col1)
WHEN MATCHED THEN UPDATE SET col2 = tab3.col2
What you are asking about is called "update through join", and contrary to a widely held belief, it is possible in Oracle. But there is a catch.
Obviously, the update - no matter how you attempt to perform it - is not well defined unless column col1 is unique in table tab2. That column is used for lookup in the update process; if its values are not unique, the update will be ambiguous. I ignore here idiotic retorts such as "uniqueness is needed only for those values also found in tab1.col1", or "there is no ambiguity as long as all values in tab2.col2 are equal when the corresponding values in tab2.col1 are equal".
The "catch" is this. The uniqueness of tab2.col1 may be a matter of data (you know it when you inspect the data), or a matter of metadata (there is a unique constraint, or a unique index, or a PK constraint, etc., on tab2.col1, which the parser can inspect without ever looking at the actual data).
merge will work even when uniqueness is only known by inspecting the data. It will still throw an error if uniqueness is violated - but that will be a runtime error (only after the data in tab2 is accessed from disk). By contrast, updating through a join requires the same uniqueness to be known ahead of time, through the metadata (or in other ways: for example if the second rowset - not a table but the table-like result of a query - is the result of an aggregation grouping on the join column; then the uniqueness is guaranteed by the definition of "aggregation").
Here is a brief example to show the difference.
Test data:
create table tab1 (col1 number, col2 number);
insert into tab1 (col1, col2) values (1, 3);
create table tab2 (col1 number, col2 number);
insert into tab2 (col1, col2) values (1, 6);
commit;
merge statement (with check at the end):
merge into tab1
using(
select tab1.col1,
tab2.col2
from tab1,tab2
where tab1.col1 = tab2.col1) tab3
on(tab1.col1 = tab3.col1)
when matched then
update
set col2 = tab3.col2;
1 row merged.
select * from tab1;
COL1 COL2
---------- ----------
1 6
Now let's restore table tab1 to its original data for the next test(s):
rollback;
select * from tab1;
COL1 COL2
---------- ----------
1 3
Update through join - with no uniqueness guaranteed in the metadata (will result in error):
update
( select t1.col2 as t1_c2, t2.col2 as t2_c2
from tab1 t1 join tab2 t2 on t1.col1 = t2.col1
)
set t1_c2 = t2_c2;
Error report -
SQL Error: ORA-01779: cannot modify a column which maps to a non key-preserved table
01779. 00000 - "cannot modify a column which maps to a non key-preserved table"
*Cause: An attempt was made to insert or update columns of a join view which
map to a non-key-preserved table.
*Action: Modify the underlying base tables directly.
Now let's add a unique constraint on the lookup column:
alter table tab2 modify (col1 unique);
Table TAB2 altered.
and try the update again (with the same update statement), plus verification:
update
( select t1.col2 as t1_c2, t2.col2 as t2_c2
from tab1 t1 join tab2 t2 on t1.col1 = t2.col1
)
set t1_c2 = t2_c2;
1 row updated.
select * from tab1;
COL1 COL2
---------- ----------
1 6
So - you can do it, if you use the correct syntax (as I have shown here) AND - very important - you have a unique or PK constraint or a unique index on column tab2.col1.
I have two tables. if the data in table1 is more than a predefined limit (say 2), i need to copy the remaining contents of table1 to table2 and delete those same contents from table1.
I used the below query to insert the excess data from table1 to table2.
insert into table2
SELECT * FROM table1 WHERE ROWNUM < ((select count(*) from table1)-2);
Now i need the delete query to delete the above contents from table1.
Thanks in advance.
A straightforward approach would be an interim storage in a temporary table. Its content can be used to determine the data to be deleted from table1 as well as the source to feed table 2.
Assume (slightly abusing notation) to be the PK column (or that of any candidate key) of table1 - usually there'll be some key that comprises only 1 column.
create global temporary table t_interim as
( SELECT <pk> pkc FROM table1 WHERE ROWNUM < ((select count(*) from table1)-2 )
;
insert into table2
select * from table1 where <pk> IN (
select pkc from t_interim
);
delete from table1 where <pk> IN (
select pkc from t_interim
);
Alternative
If any key of table1 spans more than 1 column, use an EXISTS clause instead as follows ( denoting the i-th component of a candidate key in table1):
create global temporary table t_interim as
( SELECT <ck_1> ck1, <ck_2> ck2, ..., <ck_n> ckn FROM table1 WHERE ROWNUM < ((select count(*) from table1)-2 )
;
insert into table2
select * from table1 t
where exists (
select 1
from t_interim t_i
where t.ck_1 = t_i.ck1
and t.ck_2 = t_i.ck2
...
and t.ck_n = t_i.ckn
)
;
delete from table1 t where
where exists (
select 1
from t_interim t_i
where t.ck_1 = t_i.ck1
and t.ck_2 = t_i.ck2
...
and t.ck_n = t_i.ckn
)
;
(Technically you could try to adjust the first scheme by synthesizing a key from the components of any CK, eg. by concatenating. You run the risk of introducing ambiguities ( (a bc, ab c) -> (abc, abc) ) or run into implementation limits ( max. varchar length ) using the first method)
Note
In case the table doesn't have a PK, you can apply the technique using any candidate key of table1. There will always be one, in the extreme case it's the set of all columns.
This situation may be the right time to improve the db design and add a (synthetic) pk column to table1 ( and any other tables in the system that lack it).
I have a need to do the following
UPDATE TABLE2 t2
SET t2.product_id = (select t1.product_id from
table1 t1 where t1.matching_id = t2.matching_id)
Except that TABLE2 has 27 million records. The product_id is a newly added column and hence populating data to it.
I could use a cursor , break down my record set in TABLE2 to a reasonably smaller number, But with 27 million records, I am not sure whats the best way.
Pl suggest, even if it means exporting my data to excel.
Update - THe matching columns are indexed too.
The only thing I could do different is replace the update for a CREATE TABLE AS
CREATE TABLE table2_new AS
SELECT t2.* (less product_id), t1.product_id
FROM table1 t1
JOIN table2 t2
ON t1.matching_id = t2.matching_id
But later you will have to add the CONSTRAINTS manually, delete table2 and replace for table2_new
update (select t1.product_id as old_product_id, t2.product_id as new_product_id
from table1 t1
join table2 t2 on (t1.matching_id = t2.matching_id)) t
set t.new_product_id = t.old_product_id
I want to write a query which finds the difference between two tables and writes updates or new data into third table. My two tables have identical column names. Third table which captures changes have extra column called comment. I would like to insert the comment whether it is a new row or updated row based on the row modification.
**TABLE1 (BACKUP)**
KEY,FIRST_NAME,LAST_NAME,CITY
1,RAM,KUMAR,INDIA
2,TOM,MOODY,ENGLAND
3,MOHAMMAD,HAFEEZ,PAKISTAN
4,MONIKA,SAM,USA
5,MIKE,PALEDINO,USA
**TABLE2 (CURRENT)**
KEY,FIRST_NAME,LAST_NAME,CITY
1,RAM,KUMAR,USA
2,TOM,MOODY,ENGLAND
3,MOHAMMAD,HAFEEZ,PAKISTAN
4,MONIKA,SAM,INDIA
5,MIKE,PALEDINO,USA
6,MAHELA,JAYA,SL
**TABLE3 (DIFFERENCE FROM TABLE2 TO TABLE1)**
KEY,FIRST_NAME,LAST_NAME,CITY,COMMENT
1,RAM,KUMAR,USA,UPDATE
4,MONIKA,SAM,INDIA,UPDATE
6,MAHELA,JAYA,SL,INSERT
table scripts
DROP TABLE TABLE1;
DROP TABLE TABLE2;
DROP TABLE TABLE3;
CREATE TABLE TABLE1
(
KEY NUMBER,
FIRST_NAME VARCHAR2(100),
LAST_NAME VARCHAR2(100),
CITY VARCHAR2(50)
);
/
CREATE TABLE TABLE2
(
KEY NUMBER,
FIRST_NAME VARCHAR2(100),
LAST_NAME VARCHAR2(100),
CITY VARCHAR2(50)
);
/
CREATE TABLE TABLE3
(
KEY NUMBER,
FIRST_NAME VARCHAR2(100),
LAST_NAME VARCHAR2(100),
CITY VARCHAR2(50),
COMMENTS VARCHAR2(200)
);
/
INSERT ALL
INTO TABLE1
VALUES(1,'RAM','KUMAR','INDIA')
INTO TABLE1 VALUES(2,'TOM','MOODY','ENGLAND')
INTO TABLE1 VALUES(3,'MOHAMMAD','HAFEEZ','PAKISTAN')
INTO TABLE1 VALUES(4,'MONIKA','SAM','USA')
INTO TABLE1 VALUES(5,'MIKE','PALEDINO','USA')
SELECT 1 FROM DUAL;
/
INSERT ALL
INTO TABLE2
VALUES(1,'RAM','KUMAR','USA')
INTO TABLE2 VALUES(2,'TOM','MOODY','ENGLAND')
INTO TABLE2 VALUES(3,'MOHAMMAD','HAFEEZ','PAKISTAN')
INTO TABLE2 VALUES(4,'MONIKA','SAM','INDIA')
INTO TABLE2 VALUES(5,'MIKE','PALEDINO','USA')
INTO TABLE2 VALUES(6,'MAHELA','JAYA','SL')
SELECT 1 FROM DUAL;
I was using the merge statement to accomplish the same. but i have hit a roadblock in merge statement , it's rhrowing an error "SQL Error: ORA-00905: missing keyword
00905. 00000 - "missing keyword"" I dont understand where is the error. please help
INSERT INTO TABLE3
SELECT KEY,FIRST_NAME,LAST_NAME,CITY,NULL AS COMMENTS FROM TABLE2
MINUS
SELECT KEY,FIRST_NAME,LAST_NAME,CITY,NULL AS COMMENTS FROM TABLE1
;
MERGE INTO TABLE3 A
USING TABLE1 B
ON (A.KEY=B.KEY)
WHEN MATCHED THEN
UPDATE SET A.COMMENTS='UPDATED'
WHEN NOT MATCHED THEN
UPDATE SET A.COMMENTS='INSERTED';
There is no such WHEN NOT MATCHED THEN UPDATE clause, you should use WHEN NOT MATCHED THEN INSERT. Refer to MERGE for details.
A few assumptions made about the data:
An INSERT event will be a record identified by its key in table2 (current data) that does not have a matching key in the original back-up table: table1.
An UPDATE event is a field that exists in both table1 and table2 for the same KEY but is not the same.
Records which did not change between tables are not to be recorded in table3.
Example Query: Check for Updates
SELECT UPD_QUERY.NEW_CITY, 'UPDATED' as COMMENTS
FROM (SELECT CASE WHEN REPLACE(CURR.CITY, BKUP.CITY,'') IS NOT NULL THEN CURR.CITY
ELSE NULL END as NEW_CITY
FROM table1 BKUP, table2 CURR
WHERE BKUP.KEY = CURR.KEY) UPD_QUERY
WHERE UPD_QUERY.NEW_CITY is NOT NULL;
You can repeat this comparison method for the other fields:
SELECT UPD_QUERY.*
FROM (SELECT CURR.KEY,
CASE WHEN REPLACE(CURR.FIRST_NAME, BKUP.FIRST_NAME,'') IS NOT NULL
THEN CURR.FIRST_NAME
ELSE NULL END as FIRST_NAME,
CASE WHEN REPLACE(CURR.LAST_NAME, BKUP.LAST_NAME,'') IS NOT NULL
THEN CURR.LAST_NAME
ELSE NULL END as LAST_NAME,
CASE WHEN REPLACE(CURR.CITY, BKUP.CITY,'') IS NOT NULL
THEN CURR.CITY
ELSE NULL END as CITY
FROM table1 BKUP, table2 CURR
WHERE BKUP.KEY = CURR.KEY) UPD_QUERY
WHERE COALESCE(UPD_QUERY.FIRST_NAME, UPD_QUERY.LAST_NAME, UPD_QUERY.CITY)
is NOT NULL;
NOTE: This could get unwieldy very quickly if the number of columns compared are many. Since the target table design (table3) requires not only identification of a change, but the field and its new value are also recorded.
Example Query: Look for Newly Added Records
SELECT CURR.*, 'INSERTED' as COMMENTS
FROM table2 CURR, table1 BKUP
WHERE CURR.KEY = BKUP.KEY(+)
AND BKUP.KEY is NULL;
Basically MERGE forces the operation: MATCHED=UPDATE (or DELETE), NOT MATCHED = INSERT. It's in the docs.
You can do what you want but you need two insert statements with different set operators,
For UPDATED:
Insert into table3
table1 INTERSECT table2
For INSERTED:
Insert into table3
table2 MINUS table1
I have a table ( table1 ) that represents item grouping and another table ( table2 ) that represents the items themselves.
table1.id is foreign key to table2 and in every record of table1 I also collect information like the total number of records in table2 associated with that particular record and the sum of various fields so that I can show the grouping and a summary of what's in it without having to query table2.
Usually items in table2 are added/removed one at a time, so I update table1 to reflect the changes in table2.
A new requirement arose, choosen items in a group must be moved to a new group. I thought of it as a 3 step operation:
create a new group in table1
update choosen records in table2 to point to the newly created rec in table1
the third step would be to subtract to the group the number of records / the sum of those other fields I need do show and add them to the new group, data that I can find simply querying table2 for items associated with the new group.
I came up with the following statement that works.
update table1 t1 set
countitems = (
case t1.id
when 1 then t1.countitems - ( select count( t2.id ) from table2 t2 where t2.id = 2 )
when 2 then ( select count( t2.id ) from table2 t2 where t2.id = 2 )
end
),
sumitems = (
case t1.id
when 1 then t1.sumitems - ( select sum( t2.num ) from table2 t2 where t2.id = 2 )
when 2 then ( select sum( t2.num ) from table2 t2 where t2.id = 2 )
end
)
where t1.id in( 1, 2 );
is there a way to rewrite the statement without having to repeat the subquery every time?
thanks
Piero
You can use a cursor and a bulk collect update statement on the rowid. That way you can simply write the join query with the desired result and update the table with those values. I always use this function and make slight adjustments each time.
declare
cursor cur_cur
IS
select ti.rowid row_id
, count(t2.id) countitems
, sum(t2.num) numitems
from table t1
join table t2 on t1.id = t2.t1_id
order by row_id
;
type type_rowid_array is table of rowid index by binary_integer;
type type_countitems_array is table of table1.countitems%type;
type type_numitems_array is table of table1.numitems%type;
arr_rowid type_rowid_array;
arr_countitems type_countitems_array;
arr_numitems type_numitems_array;
v_commit_size number := 10000;
begin
open cur_cur;
loop
fetch cur_cur bulk collect into arr_rowid, arr_countitems, arr_numitems limit v_commit_size;
forall i in arr_rowid.first .. arr_rowid.last
update table1 tab
SET tab.countitems = arr_countitems(i)
, tab.numitems = arr_numitems(i)
where tab.rowid = arr_rowid(i)
;
commit;
exit when cur_cur%notfound;
end loop;
close cur_cur;
commit;
exception
when others
then rollback;
raise_application_error(-20000, 'ERROR updating table1(countitems,numitems) - '||sqlerrm);
end;