I have table called company_emp. In that table I have 6 columns related to employees:
empid
ename
dob
doj, ...
I have another table called bday. In that I have only 2 columns; empid and dob.
I have this query:
select empid, dob
from company_emp
where dob like '01/05/2011'
It shows some list of employees.
In the same way I have queried with table bday it listed some employees.
Now I want to update the company_emp table for employees who have date '01/05/2011'.
I have tried a query like this:
update company_name a
set dob = (select dob from bday b
where b.empid=a.empid
and to_char(a.dob,'dd/mm/yyyy') = '01/05/2011'}
Then all the records in that row becoming null. How can I fix this query?
You're updating every row in the company_name/emp table.
You can fix that with a correlated subquery to make sure the row exists, or more efficiently by placing a primary or unique key on bday.empid and querying:
update (
select c.dob to_dob,
d.dob from_dob
from company_emp c join dob d on (c.empid = d.empid)
where d.dob = date '2011-05-01')
set to_dob = from_dob
Syntax not tested.
Related
I'm trying to update data in 2 distinct tables in the same query with the following code:
UPDATE (SELECT s.passNumb, a.hour, a.minute, p.number, s.situation
FROM passwords s
JOIN atend a ON s.passNumb = a.passNumb
JOIN points p ON a.number = p.number
WHERE s.passNumb = 1 AND
p.number = 1)
SET a.hour = TO_CHAR(SYSDATE, 'HH24'),
a.minute = TO_CHAR(SYSDATE, 'MI'),
s.situation = 'F';
But I'm getting this error: Cannot modify a column which maps to a non key-preserved table. What am I doing wrong?
A view with a join (or an inline view containing a join in your case) must meet the following conditions to be updatable:
https://docs.oracle.com/cd/B28359_01/server.111/b28286/statements_8004.htm
If you want a join view to be updatable, then all of the following
conditions must be true:
The DML statement must affect only one table underlying the join.
For an INSERT statement, the view must not be created WITH CHECK
OPTION, and all columns into which values are inserted must come from
a key-preserved table. A key-preserved table is one for which every
primary key or unique key value in the base table is also unique in
the join view.
For an UPDATE statement, the view must not be created WITH CHECK
OPTION, and all columns updated must be extracted from a key-preserved
table.
The first condition is rather obvious: The DML statement must affect only one table underlying the join.
But what does it mean: "key preserved table" ?
A key-preserved table is one for which every primary key or unique
key value in the base table is also unique in the join view.
The key preserved table means that each row from this table will appear at most once in the result of a view.
Consider a simple example:
CREATE TABLE users(
user_id int primary key,
user_name varchar(100),
age int
);
insert into users values(1,'Tom', 22);
CREATE TABLE emails(
user_id int,
email varchar(100)
);
Insert into emails values( 1, 'tom#somedomain.com' );
Insert into emails values( 1, 'tom#www.example.org' );
commit;
And a join:
SELECT *
FROM users u
JOIN emails e ON u.user_id = e.user_id;
USER_ID USER_NAME AGE USER_ID EMAIL
---------- --------------- ---------- ---------- --------------------
1 Tom 22 1 tom#somedomain.com
1 Tom 22 1 tom#www.example.org
If you look at a result of this join, it is apparent that:
user_id, user_name and age come from non-key preserved table
email comes from key-preserved table
And now: this update is acceptable, because it updates a key preserved column (table) in this join:
UPDATE (
SELECT * FROM users u
JOIN emails e ON u.user_id = e.user_id
)
SET email = email || '.it' ;
USER_ID USER_NAME AGE USER_ID EMAIL
---------- --------------- ---------- ---------- -------------------------
1 Tom 22 1 tom#somedomain.com.it
1 Tom 22 1 tom#www.example.org.it
But this update cannot be done, since it touches a column from non-key preserved table:
UPDATE (
SELECT * FROM users u
JOIN emails e ON u.user_id = e.user_id
)
SET age = age + 2;
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.
If you think a while .... Tom appears 2 times in the result of the join (but there is only one Tom in the users table).
When we are trying to update age = age + 2 in this join, then what should be a result of this update ?
Should Tom be updated only once ?
Should Tom be 22+2 = 24 years old after this update ?
Or maybe Tom should be updated twice (since it appears twice in the result of the join) so it should be 22 + 2 + 2 = 26 years old.
Another example - please tell me what should be an outcome of this update?:
UPDATE ( ....our join ... ) SET age = length( email );
There are very difficult questions :)
And because of this Oracle prevents from updating non-key preserved tables.
The error message gives this hint:
*Action: Modify the underlying base tables directly.
This means that we must update this table directly, using a separate UPDATE command:
UPDATE users SET age = age + 2
I have two db2 tables, table one contains rows of constant data with id as one of the columns. second table contains id column which is foreign key to id column in first table and has 3 more varchar columns.
I am trying to insert rows into second table, where entry into id col is based on a where clause and the remaining columns get values from outside.
table1 has columns id, t1c1, t1c2, t1c3
table2 has columns id, t2c1, t2c2, t2c3
to insert into table2, I am trying this query:
insert into table2 values
(select id from table1 where t1c2 like 'xxx', 'abc1','abc2');
I know it is something basic I am missing here.
Please help correcting this query.
I have two table like as shown below, first one is employee having columns
empid empname empstaus
and second is table is bbb
eempid empdept empworty
both the table are joined in id basis
now I have to do a sort of filetering as in emp table staus can be a value or null so for a
employee whose value is null I need to check in other table bbb and print all the details only for emplyees whose staus is null in emp table please advise how to achieve this , i am using oracle as a database
If I understand correctly try
SELECT b.*
FROM bbb b JOIN employee e
ON b.eempid = e.empid
WHERE e.empstatus IS NULL
Here is SQLFiddle demo.
I have a table
CREATE TABLE STUDENT
(
ID INTEGER PRIMARY KEY,
FIRSTNAME VARCHAR2(1024 CHAR),
LASTNAME VARCHAR2(1024 CHAR),
MODIFIEDDATE DATE DEFAULT sysdate
)
I am inserting a row of data
insert into STUDENT (ID, FIRSTNAME, LASTNAME, MODIFIEDDATE) values (1,'Scott', 'Tiger', sysdate);
When I have to insert a record of data, I need to write a procedure or function which does the following:
if there is no record for the same id insert the row.
if there is a record for the same id and data matches then do nothing.
if there is a record for the same id but data does not match then update the data.
I am new to oracle. From the java end, It is possible to select the record by id and then update that record, but that would make 2 database calls. just to avoid that I am trying update the table using a procedure. If the same can be done in a single database call please mention.
For a single SQL statement solution, you can try to use the MERGE statement, as described in this answer https://stackoverflow.com/a/237328/176569
e.g.
create or replace procedure insert_or_update_student(
p_id number, p_firstname varchar2, p_lastname varchar2
) as
begin
merge into student st using dual on (id = p_id)
when not matched then insert (id, firstname, lastname)
values (p_id, p_firstname, p_lastname)
when matched then update set
firstname = p_firstname, lastname = p_lastname, modifiedate = SYSDATE
end insert_or_update_student;
instead of procedure try using merge in oracle .
If Values is matched it will update the table and if values is not found it will insert the values
MERGE INTO bonuses b
USING (
SELECT employee_id, salary, dept_no
FROM employee
WHERE dept_no =20) e
ON (b.employee_id = e.employee_id)
WHEN MATCHED THEN
UPDATE SET b.bonus = e.salary * 0.1
DELETE WHERE (e.salary < 40000)
WHEN NOT MATCHED THEN
INSERT (b.employee_id, b.bonus)
VALUES (e.employee_id, e.salary * 0.05)
WHERE (e.salary > 40000)
Try this
To solve the second task - "if there is a record for the same id and data matches then do nothing." - starting with 10g we have additional "where" clause in update and insert sections of merge operator.
To do the task we can add some checks for data changes:
when matched then update
set student.last_name = query.last_name
where student.last_name <> query.last_name
This will update only matched rows, and only for rows where data were changed
In Oracle I have two tables. Both are populated with data and have a timestamp column.
One table has that column filled with data, the other table doesn't. But I need to get the data from the table that does into the column of the other table based on a match of another column.
Each has 'code' so the timestamp from the one table should only be put in the timestamp of the other table where the codes match.
I've tried cursors etc, but it seems like I'm missing something.
Any suggestions?
It sounds like you want a correlated update. This will update every row of destinationTable with the timestamp_col from sourceTable where there is a match on the code column.
UPDATE destinationTable d
SET timestamp_col = (SELECT s.timestamp_col
FROM sourceTable s
WHERE s.code = d.code )
WHERE EXISTS( SELECT 1
FROM sourceTable s
WHERE s.code = d.code )
Just for completeness, I think I would have done something like this (untested), if the destination has a primary key or unique column:
UPDATE (
SELECT d.primary_key AS pk, d.timestamp_col AS dest_col, MAX(s.timestamp_col) AS src_col
FROM dest d
JOIN src s ON d.code = s.code
GROUP BY pk, dest_col
) j
SET j.dest_col = j.src_col