This is so simple it has probably already been asked, but I couldn't find it (if that's the case I'm sorry for asking).
I would like to insert an empty row on a table so I can pick up its ID (primary key, generated by an insert trigger) through an ExecuteScalar. Data is added to it at a later time in my code.
My question is this: is there a specific insert syntax to create an empty record? or must I go with the regular insert syntax such as "INSERT INTO table (list all the columns) values (null for every column)"?
Thanks for the answer.
UPDATE: In Oracle, ExecuteScalar on INSERT only returns 0. The final answer is a combination of what was posted below. First you need to declare a parameter, and pick up it up with RETURNING.
INSERT INTO TABLENAME (ID) VALUES (DEFAULT) RETURNING ID INTO :parameterName
Check this out link for more info.
You would not have to specify every single column, but you may not be able to create an "empty" record. Check for NOT NULL constraints on the table. If none (not including the Primary Key constraint), then you would only need to supply one column. Like this:
insert into my_table ( some_column )
values ( null );
Do you know about the RETURNING clause? You can return that PK back to your calling application when you do the INSERT.
insert into my_table ( some_column )
values ( 'blah' )
returning my_table_id into <your_variable>;
I would question the approach though. Why create an empty row? That would/could mean there are no constraints on that table, a bad thing if you want good, clean, data.
Basically, in order to insert a row where values for all columns are NULL except primary
key column's value you could execute a simple insert statement:
insert into your_table(PK_col_name)
values(1); -- 1 for instance or null
The before insert trigger, which is responsible for populating primary key column will
override the value in the values clause of the insert statement leaving you with an
empty record except PK value.
Related
I am trying to replace all of the NULL values to 0 in a column of a big table in HIVE.
However, every time I try to implement some code I end up generating a new column to the table. The column I am trying to change/modify still exists and still has the NULL values but the new column that is automatically generated (i.e. _c1) is what I want the column I am trying to modify, to look like.
I tried to run a COALESCE but that also ended up generating a new column. I also tried to implement a CASE WHEN, but the same results ensued.
Select *,
CASE WHEN columnname IS NULL THEN 0
ELSE columnname
END
from tablename;
Also tried
SELECT coalesce(columnname, CAST(0 AS BIGINT)) FROM tablename
I would just like to update the table with the other columns being as is but the column I want to modify still has its original name but instead of NULL values it has 0's that replaced them.
I don't want to generate a new column but modify an existing one.
How should I do that?
Use insert overwrite .. option.
insert overwrite table tablename
select c1,c2,...,coalesce(columnname,0) as columnname
from tablename
Note that you have to specify all the other column names required in select.
I am new to Oracle. I have a table in Oracle which has 4 columns Period, Open_Flag,Creation_Dt,Updated_By.
The Period column is the Primary key of the table. I have created a proc which will check the value of period from input parameter in the table, if its existing, the value of Open_flag has to be updated else a new record shall be inserted.
create or replace
PROCEDURE PROC_REF_SAP_PERIOD(
V_PERIOD IN NUMBER,V_OPEN_FLAG IN VARCHAR2,V_CREATION_DT IN DATE,V_UPDATED_BY IN VARCHAR2)
AS
BEGIN
MERGE INTO REF_SAP_PERIOD T
USING (SELECT * FROM REF_SAP_PERIOD WHERE PERIOD=V_PERIOD )S
ON (T.PERIOD=S.PERIOD )
WHEN MATCHED THEN UPDATE SET OPEN_FLAG = V_OPEN_FLAG --WHERE PERIOD=V_PERIOD AND CREATION_DT=V_CREATION_DT AND UPDATED_BY=V_UPDATED_BY
WHEN NOT MATCHED THEN INSERT (PERIOD,OPEN_FLAG,CREATION_DT,UPDATED_BY) VALUES (V_PERIOD,V_OPEN_FLAG,V_CREATION_DT,V_UPDATED_BY);
END;
The issue is that the Update is working well in this case, however, the insert is not working. Please help.
You are merging table with itself, filtered by period. Obviously, it will never see your non-existent values in itself.
Try this line instead of your USING line:
using (select V_PERIOD "period" from dual)S
table 1
ID - name - main_number - random1 - random2
1* -aaaa-blalablabla*- *** - *
2 -vvvv-blublubluuu*- *** - *
3 -aaaa-blalablabla*- *** - **
ID , name and main number are primary key
My problem that I have noticed coulmn name and main number has duplicate values, i dont want to ADD ANY OTHER DUPLICATE VALUES ( I should keep the old duplicat because in my real table there are a lot of duplicated data and its hard to remove them )
what I want when I TRY ( BEFORE TO COMMIT) to know that this name I am trying to insert is duplicate.
I can do that with in a procedure or triger, but i have heard constraint checking is simpler and easier(if there a simpler way then procedure or triger ill be glad to learn it)
CONSTRAINT check_name
CHECK (name = (A_name))
can the constaraint have more then 1 column in such way?
CONSTRAINT check_name
CHECK (name = (A_name) , main_number=( A_number))
can I a write a constaraint in such way?
CONSTRAINT check_name
CHECK (name = ( select case where there is an column has the same value of column name))
So my question : Is there a way simelar to check constraint to help me to know if there is a duplicate column or I have to use a trigger ?
Since your database is Oracle you could also use NOVALIDATE constraints. Meaning: "doesn't matter how the data is, just validate from now on".
create table tb1
(field1 number);
insert into tb1 values (1);
insert into tb1 values (1);
insert into tb1 values (1);
insert into tb1 values (2);
insert into tb1 values (2);
commit;
-- There should be an non-unique index first
create index idx_t1 on tb1 (field1);
alter table tb1 add constraint pk_t1 primary key(field1) novalidate;
-- If you try to insert another 1 or 2 you would get an error
insert into tb1 values (1);
Yes, you can use constraints on many columns.
But in this case constraint is not applicable, because all table rows must satisfy constraints. Use a trigger.
Constraints cannot contain subqueries.
Alternatively use unique index, that will enforce unique constraint
create unique index index1 on table1
(case when ID <= XXX then null else ID end,
case when ID <= XXX then null else name end);
Replace 'XXX' with your current max(ID).
I assume that you want to prevent duplicate records as defined by the combination of name and main_number.
Then the way to go is to cleanup your database, and create a unique index:
create unique index <index_name> on <table> (name, main_number)
This both checks, and speed's it up.
In theory, if you really wanted to keep the old duplicate records, you could get along by using a trigger, but then you will have a hard time trying to get sense out of this data.
Update
If you used the trigger, you would end up with two partitions of data in one table - one is checked, the other is not. So all of your queries must pay attention to it. You just delay your problem.
So either clean it up (by deleting or merging) or move the old data in a separate table.
You can use SQL select ... group by to find your duplicates, so you can delete/move them in one turn.
I'm looking for the best way to change a data type of a column in a populated table. Oracle only allows changing of data type in colums with null values.
My solution, so far, is a PLSQL statement which stores the data of the column to be modified in a collection, alters the table and then iterates over the collection, restoring the original data with data type converted.
-- Before: my_table ( id NUMBER, my_value VARCHAR2(255))
-- After: my_table (id NUMBER, my_value NUMBER)
DECLARE
TYPE record_type IS RECORD ( id NUMBER, my_value VARCHAR2(255));
TYPE nested_type IS TABLE OF record_type;
foo nested_type;
BEGIN
SELECT id, my_value BULK COLLECT INTO foo FROM my_table;
UPDATE my_table SET my_value = NULL;
EXECUTE IMMEDIATE 'ALTER TABLE my_table MODIFY my_value NUMBER';
FOR i IN foo.FIRST .. foo.LAST
LOOP
UPDATE my_table
SET = TO_NUMBER(foo(i).my_value)
WHERE my_table.id = foo(i).id;
END LOOP;
END;
/
I'm looking for a more experienced way to do that.
The solution is wrong. The alter table statement does an implicit commit. So the solution has the following problems:
You cannot rollback after alter the alter table statement and if the database crashes after the alter table statement you will loose data
Between the select and the update users can make changes to the data
Instead you should have a look at oracle online redefinition.
Your solution looks a bit dangerous to me. Loading the values into a collection and subsequently deleting them fom the table means that these values are now only available in memory. If something goes wrong they are lost.
The proper procedure is:
Add a column of the correct type to the table.
Copy the values to the new column.
Drop the old column.
Rename the new column to the old columns name.
In Oracle, given a simple data table:
create table data (
id VARCHAR2(255),
key VARCHAR2(255),
value VARCHAR2(511));
suppose I want to "insert or update" a value. I have something like:
merge into data using dual on
(id='someid' and key='testKey')
when matched then
update set value = 'someValue'
when not matched then
insert (id, key, value) values ('someid', 'testKey', 'someValue');
Is there a better way than this? This command seems to have the following drawbacks:
Every literal needs to be typed twice (or added twice via parameter setting)
The "using dual" syntax seems hacky
If this is the best way, is there any way around having to set each parameter twice in JDBC?
I don't consider using dual to be a hack. To get rid of binding/typing twice, I would do something like:
merge into data
using (
select
'someid' id,
'testKey' key,
'someValue' value
from
dual
) val on (
data.id=val.id
and data.key=val.key
)
when matched then
update set data.value = val.value
when not matched then
insert (id, key, value) values (val.id, val.key, val.value);
I would hide the MERGE inside a PL/SQL API and then call that via JDBC:
data_pkg.merge_data ('someid', 'testKey', 'someValue');
As an alternative to MERGE, the API could do:
begin
insert into data (...) values (...);
exception
when dup_val_on_index then
update data
set ...
where ...;
end;
I prefer to try the update before the insert to save having to check for an exception.
update data set ...=... where ...=...;
if sql%notfound then
insert into data (...) values (...);
end if;
Even now we have the merge statement, I still tend to do single-row updates this way - just seems more a more natural syntax. Of course, merge really comes into its own when dealing with larger data sets.