I have an encountered an issue where the data I was trying to store in my varchar2(4000) column was too big, so I wish to change the column to one more suitable for storing large amounts of textual data. Specifically, a serialized array.
Firstly, is CLOB the best data type for me to use for this purpose? Is there a more appropriate data type?
Secondly, when I try to alter the column using the usual snyntax:
ALTER TABLE table MODIFY column CLOB
I get the following error: ORA-22858: invalid alteration of datatype
What's the most straightforward way to alter this table without losing any data?
The most straightforward way, given that the operation of moving from a varchar column to a CLOB is disallowed, would be to create a new column and move the data from the old column to the new column:
ALTER TABLE some_table ADD (foo CLOB);
UPDATE some_table SET foo = old_column;
ALTER TABLE some_table DROP COLUMN old_column;
ALTER TABLE some_table RENAME COLUMN foo TO old_column;
The VARCHAR2 column cannot be directly converted to CLOB but it can be done in 2 steps:
Convert column datatype from VARCHAR2 to LONG.
Convert column datatype from LONG to CLOB.
ALTER TABLE table MODIFY column long;
ALTER TABLE table MODIFY column clob;
For Oracle 11g:
ALTER TABLE table MODIFY column long;
ALTER TABLE table MODIFY column clob;
Related
Question about Oracle - pl/sql.
is it possible to create a procedure that takes the name of the table as parameter, it retrieves the columns of the table and asks for the values of each column and then it insert the data.
if it is possible how can i do it?
How can I change DATA TYPE of a column from number to varchar2 without deleting the table data?
You can't.
You can, however, create a new column with the new data type, migrate the data, drop the old column, and rename the new column. Something like
ALTER TABLE table_name
ADD( new_column_name varchar2(10) );
UPDATE table_name
SET new_column_name = to_char(old_column_name, <<some format>>);
ALTER TABLE table_name
DROP COLUMN old_column_name;
ALTER TABLE table_name
RENAME COLUMN new_column_name TO old_coulumn_name;
If you have code that depends on the position of the column in the table (which you really shouldn't have), you could rename the table and create a view on the table with the original name of the table that exposes the columns in the order your code expects until you can fix that buggy code.
You have to first deal with the existing rows before you modify the column DATA TYPE.
You could do the following steps:
Add the new column with a new name.
Update the new column from old column.
Drop the old column.
Rename the new column with the old column name.
For example,
alter table t add (col_new varchar2(50));
update t set col_new = to_char(col_old);
alter table t drop column col_old cascade constraints;
alter table t rename column col_new to col_old;
Make sure you re-create any required indexes which you had.
You could also try the CTAS approach, i.e. create table as select. But, the above is safe and preferrable.
The most efficient way is probably to do a CREATE TABLE ... AS SELECT
(CTAS)
alter table table_name modify (column_name VARCHAR2(255));
Since we can't change data type of a column with values, the approach that I was followed as below,
Say the column name you want to change type is 'A' and this can be achieved with SQL developer.
First sort table data by other column (ex: datetime).
Next copy the values of column 'A' and paste to excel file.
Delete values of the column 'A' an commit.
Change the data type and commit.
Again sort table data by previously used column (ex: datetime).
Then paste copied data from excel and commit.
I am using XMLType column in some of my oracle database table. Earlier(in 11.2.0.2) the default storage type considered is CLOB. So If you issue a query for the XMLType columns, I can see the content of the column as XML string. But when I drop and re-create all the tables and inserted some data, I could not get the content of the XMLType columns. It simpley display the XMLType in the cloumn value. I have a doubt that whether the storage type is chaged in BINARY XML? So I issue the following alter statement:
ALTER TABLE "MYSCHEMA"."SYSTEMPROP"
MODIFY ("XMLCOL")
XMLTYPE COLUMN "XMLCOL" STORE AS CLOB;
Please note that there are already some data present in the table. Event after when I delete and insert a row, the content is showing as XMLType. I am using SQL developer UI tool. Can anybody suggest a way to fix this issue?
Edit:
Ok, Now we have decided that we will store the XMLType column content as SECURE FILE BINARY XML. So we have table like this:
CREATE TABLE XMYTYPETEST
(
ID NUMBER(8) NOT NULL,
VID NUMBER(4) NOT NULL,
UserName VARCHAR2(50),
DateModified TIMESTAMP(6),
Details XMLType
)XMLTYPE COLUMN Details STORE AS SECUREFILE BINARY XML;
Insert into XMYTYPETEST values(10001,1,'XXXX',sysdate,'<test><node1>BLOBTest</node1></test>');
Select * from XMYTYPETEST;
The XMLType colum is displayed as "SYS.XMLType" in sql developer. So how to get the content of the binary XML?
Edit:
SELECT x.ID,x.Vid, x.details.getCLOBVal() FROM XMYTYPETESTx where x.ID=100000;
The above query works out for me finally.
The underlying storage for xmldata inside oracle database is either CLOB or Binary.
And it defaults to Binary storage in 11g.
But irrespective of the storage, your queries on the xmltype column should yield you consistent results.
>>>> So how to get the content of the binary XML?
The way to get the content of an xmltype column using queries does not change.
select xmlquery(..)
select xmlcast(xmlquery(...))
select extract(), extractValue(), ...
These are some of the ways data within xml is extracted.
Hope this helps.
I am trying to add a CLOB column to a table (change a VARCHAR to a CLOB actually, but it only seems possible by adding a new column, copying and dropping the old). The column should be NOT NULL without a default value (and the table is not empty). How can I achieve this?
My original idea was to create the column with a dummy default, and change that later, but that does not seem possible:
ALTER TABLE foo RENAME COLUMN text TO text_temp;
ALTER TABLE foo ADD (
text CLOB DEFAULT '*' NOT NULL
);
UPDATE foo SET text = text_temp;
ALTER TABLE foo DROP COLUMN text_temp;
ALTER TABLE foo MODIFY (
text CLOB NOT NULL
);
-- ORA-22296: invalid ALTER TABLE option for conversion of LONG datatype to LOB
I also tried defining the column as text CLOB and adding the NOT NULL constraint later, but it gave the same error. Is there a way of doing this, short of recreating the whole table?
Does
ALTER TABLE foo MODIFY text DEFAULT NULL;
work for you?
When adding or removing a default value or a NOT NULL constraint, you don't need to specify the datatype of the column.
EDIT: To quote the Oracle documentation on ALTER TABLE:
If a column has a default value, then you can use the DEFAULT clause to change the default to NULL, but you cannot remove the default value completely. If a column has ever had a default value assigned to it, then the DATA_DEFAULT column of the USER_TAB_COLUMNS data dictionary view will always display either a default value or NULL.
This should explain why you're seeing a difference in SQL Developer.
However, I don't believe there's a significant difference between specifying DEFAULT NULL for a column and not specifying a default value. In both cases, a null value will be assumed for any column not explicitly given a value in an INSERT statement.
You are declaring the column as NOT NULL when you added it to the table, so you don't need to make it NOT NULL again. I think if you corrected the syntax in the final MODIFY clause you would still get an error, albeit a different one (precise number eludes me right now).
But what you are trying to acheive is definitely possible, with the right syntax :)
SQL> alter table t23 add ctxt clob
2 /
Table altered.
SQL> update t23 set ctxt = txt
2 /
2 rows updated.
SQL> alter table t23 modify ctxt not null
2 /
Table altered.
SQL> alter table t23 drop column txt
2 /
Table altered.
SQL> alter table t23 rename column ctxt to txt
2 /
Table altered.
SQL>
I have created a table in oracle XE, and I have a field with type date. I would like if possible when I insert a row, that it automatically fills that field with the current date from the system.
I am inserting the rows from the SQL prompt.
Thanks
Here is how, you need to format your table properly:
create table test (first number
, second timestamp default systimestamp
, third varchar2(12));
And your default value is always current system time formatted as timestamp.
change the field after creating the table
ALTER TABLE table MODIFY time_collumn TIMESTAMP DEFAULT CURRENT_TIMESTAMP;
Or you could also use a trigger:
CREATE OR REPLACE TRIGGER date_trigger
BEFORE INSERT
ON table_name
REFERENCING NEW AS NEW
FOR EACH ROW
BEGIN
SELECT sysdate INTO :NEW.column_name FROM dual;
END;
The below snippet might be helpful if we forget to add the constraint while creating the table:
ALTER TABLE TABLE_NAME
ADD CONSTRAINT CONSTRAINT_NAME
COLUMN_NAME DATA_TYPE DEFAULT CURRENT_DATE;