I am trying to alter a table where the original datatype of this column is Number to a generated column, but I get an error of "ORA-00905 Missing Keyword"
Alter Table MyTable
Modify Column FlagColumn NUMERIC (38,0) GENERATED ALWAYS AS (CASE WHEN ValueColumn IS NULL THEN 1 ELSE 0 END) VIRTUAL;
Is my syntax correct?
Do I have any other options besides dropping and recreating the table?
The Oracle documentation pretty clearly doesn't support the syntax you're attempting. The obvious solution is to drop the column, then replace it:
ALTER TABLE mytable
DROP COLUMN flagcolumn;
ALTER TABLE mytable
ADD numeric GENERATED ALWAYS AS (CASE WHEN valuecolumn IS NULL THEN 1 ELSE 0 END) VIRTUAL;
There's really no reason not to do this, since you're getting rid of the column's original data in any case.
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 trying to drop a column from a table in Oracle using a statement like this:
ALTER TABLE "MY_TABLE" DROP COLUMN "ENABLED";
but I am getting this error:
ORA-12899: value too large for column "MY_TABLE"."ENABLED" (actual: 184, maximum: 22)
The column is defined as
"ENABLED" NUMBER(1,0) DEFAULT NULL NOT NULL ENABLE,
and it only has values of 0 or 1 in all the rows.
Can anyone tell me why I am getting this error and how to drop the column?
You can try setting it unused first, then dropping unused columns. For more, see Marking Columns Unused.
You maybe have some rows with incorrect encoding, you may want to try a FLIP/FLOP:
-Create a table NEW_MY_TABLE with the same structure as MY_TABLE, but without "ENABLED" Column.
-Make an Insert Into NEW_MY_TABLE (col1,col2...) Select (Col1,Col2...) from MY_TABLE
-Rename MY_TABLE to MY_TABLE_OLD
-Rename NEW_MY_TABLE to MY_TABLE
-Drop MY_TABLE_OLD
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.
why I am getting this error ?
In the table DDL I only have 2 columns , id (number) and name (varchar)
ALTER TABLE mytable ADD SUSPEND date NOT NULL
ORA-01758: table must be empty to add mandatory (NOT NULL) column
ORA-06512: at line 7
ORA-01758: table must be empty to add mandatory (NOT NULL) column ORA-06512: at line 7
And is your table empty? I think not.
There's probably a way around this involving adding the column as nullable, then populating every row with a non-NULL value, the altering the column to be not null.
Alternatively, since the problem is that these current rows will be given NULL as a default value, and the column is not allowed to be NULL, you can also get around it with a default value. From the Oracle docs:
However, a column with a NOT NULL constraint can be added to an existing table if you give a default value; otherwise, an exception is thrown when the ALTER TABLE statement is executed.
Here is a fiddle, how you could do it
Would a date in the future be acceptable as a temporary default? If so, this would work:
ALTER TABLE MYTABLE ADD (SUSPEND_DATE DATE DEFAULT(TO_DATE('21000101', 'YYYYMMDD'))
CONSTRAINT SUSPEND_DATE_NOT_NULL NOT NULL);
If table already contain the records then table won't allowes to add "Not null" column.
If you need same then set default value for the column or truncate the table then try.
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.