I've got to store multiple text fields of variable length in an oracle database. I'd need to define them as columns of the same table to be able to order the results when I query it.
I can't know the max size of the field contents, most of them will be less than 100 characters but there could be some of thousands of chars. Furthermore the number of fields changes dinamically.
I was thinking of defining a table with multiple NCLOB columns that would allow me to store anything in them (very short and very long texts) But I wonder if this would be the right design.
Summary:
Variable number of fields (metadata of the same object)
Variable length of the content
I need to order the results
Thanks
KL
When you need variable number of fields, it's better to split the table into parent and child. Then you can effectively have any number of fields. And you can add order column to store ordering information to order the result. You can query by joining the two table and use order by clause to order the result. Also you can add foreign key constraint to make sure the relationship and data integrity.
In the case of variable length of contents, you can use varchar2(or nvarchar2) to store text date. Varchar2 can hold characters up to 4000 bytes. If you know that the maximum length of the content can be longer than 4000 bytes, you should use CLOB(or NCLOB).
Related
I would like to spare some tables in my database.
One table for example has a simple Primary-Key-ID column and a VARCHAR2 column.
The VARCHAR2 column has NO duplicate values, yet different unique IDs.
The PK column of this table is just referenced once as a foreign key in another table.
My thoughts are now to insert the values from the VARCHAR2 column into the the table which has held the primary key.
I could now remove the foreign key reference, delete the table and gain a new column with all the (duplicate) VARCHAR2 values. These I would like to compress in a unique/distinct way.
I have heard about index in the Oracle Database to compress column(s) but I am not quite sure which index I need or how to use them...
The underlying feature (and storage savings) should be about as the same as it was with the previous table of unique values and the foreign key reference.
Thank you for your help in advance!
Oracle basic compression allows us to compress tables. It comes with several distinct limitations, not the least of which is that it isn't suitable for OLTP databases. Direct path inserts, updates and deletes don't benefit. So you can't do what you want that way. If your organisation has sprung for the Advanced Compression licence then you have more options, but the compression still works on the table not an individual column.
I think you've confused things with index compression, which does operate on columns, as it allows us to compress the leading column(s) of a compound index. But it's worth applying only when there's a lot of repetition in those columns. If your index has a unique ID for the leading column than compression will actually increase the total amount of space taken. (Just one reason why compound indexes should be built with the least selective column first and the most selective column last.)
Your table is a classic key-value lookup table. So you could consider converting it into an index-organized table. You would save yourself a bit of space by maintaining only a specialized index instead of a table and its primary key index. Find out more
I have written query to generate a random 8 digit nummber and then i am inserting values into a table. The numbers generated should be unique.
Example: Say below is query, this generates random 8 digit number, and then i am inserting it into table temp. Now everytime before inserting into the table how do i need to check if the number generated from below query is alredy in temp table?
Using for loop doesnt seem to be useful as it will cause lag when there are going to be lot of transactions at same time. Any other suggestions like goto, if number is already in table can we use goto and then redirect it to same query until we get a unique value?
Query:
select trunc(dbms_random.value(10000000,99999999))
into v_customer_nbr
from dual;
If you are looking for unique values then you should rather consider using SYS_GUID instead. SYS_GUID generates and returns a globally unique identifier made up of 16 bytes.
I have a large table of 7 column in Oracle 11G. Total size of the table is more than 3GB and total row in this table is 1876823. Query we are using
select doc_mstr_id from index_mstr where page_con1 like('%sachin%') it is taking almost a minute. please help me to optimize the query as well as proper indexing for this table. Please let me know if partitioned is required for this table.
Below are the column description
INDEX_MSTR_ID NUMBER
DOC_MSTR_ID NUMBER
PAGE_NO NUMBER
PAGE_PART NUMBER
PAGE_CON1 VARCHAR2(4000)
FILE_MODIFIED_DATE DATE
CREATED_DATE DATE
This query is always going to result in a full table scan. Your only filter cannot use a B-TREE index, due to the leading wildcard:
where page_con1 like('%sachin%')
If you want to do lots of queries of this nature you need to build a Text index on that column. From its datatype page_con1 appears to hold text fragments rather than full documents so you should use a CTXCAT index. This type of index has the advantage of being transactional, rather than requiring background maintenance. Find out more.
Your query would then look like this:
select doc_mstr_id from index_mstr
WHERE CATSEARCH(page_con1, 'sachin') > 0;
I have a massive table in which I can't do any more partitioning or sub-partitioning, nor am allowed to do any alter. I want to query its records by batches, and thought a good way would be using the last two digits from the account numbers (wouldn't have any other field splitting records as evenly).
I guess I'd need to at least index that somehow (remember I can't alter table to add a virtual column either).
Is there any kind of index to be used in such situation?
I am using Oracle 11gR2
You can use function based index:
create index two_digits_idx on table_name (substr(account_number, -2));
This index will work only in queries like that:
select ...
from table_name t ...
where substr(account_number, -2) = '25' -- or any other two digits
For using index, you need to use in a query the same expression like in an index.
We have a table in Oracle 11g with a varchar2 column. We use a proprietary programming language where this column is defined as string. Maximum we can store 2000 characters (4000 bytes) in this column. Now the requirement is such that the column needs to store more than 2000 characters (in fact unlimited characters). The DBAs don't like BLOB or LONG datatypes for maintenance reasons.
The solution that I can think of is to remove this column from the original table and have a separate table for this column and then store each character in a row, in order to get unlimited characters. This tble will be joined with the original table for queries.
Is there any better solution to this problem?
UPDATE: The proprietary programming language allows to define variables of type string and blob, there is no option of CLOB. I understand the responses given, but I cannot take on the DBAs. I understand that deviating from BLOB or LONG will be developers' nightmare, but still cannot help it.
UPDATE 2: If maximum I need is 8000 characters, can I just add 3 more columns so that I will have 4 columns with 2000 char each to get 8000 chars. So when the first column is full, values would be spilled over to the next column and so on. Will this design have any bad side effects? Please suggest.
If a blob is what you need convince your dba it's what you need. Those data types are there for a reason and any roll your own implementation will be worse than the built in type.
Also you might want to look at the CLOB type as it will meet your needs quite well.
You could follow the way Oracle stored their stored procedures in the information schema. Define a table called text columns:
CREATE TABLE MY_TEXT (
IDENTIFIER INT,
LINE INT,
TEXT VARCHAR2 (4000),
PRIMARY KEY (INDENTIFIER, LINE));
The identifier column is the foreign key to the original table. The Line is a simple integer (not a sequence) to keep the text fields in order. This allows keeping larger chunks of data
Yes this is not as efficient as a blob, clob, or LONG (I would avoid LONG fields if at all possible). Yes, this requires more mainenance, buf if your DBAs are dead set against managing CLOB fields in the database, this is option two.
EDIT:
My_Table below is where you currently have the VARCHAR column you are looking to expand. I would keep it in the table for the short text fields.
CREATE TABLE MY_TABLE (
INDENTIFER INT,
OTHER_FIELD VARCHAR2(10),
REQUIRED_TEXT VARCHAR(4000),
PRIMERY KEY (IDENTFIER));
Then write the query to pull the data join the two tables, ordering by LINE in the MY_TEXT field. Your application will need to split the string into 2000 character chunks and insert them in line order.
I would do this in a PL/SQL procedure. Both insert and select. PL/SQL VARCHAR strings can be up to 32K characters. Which may or may not be large enough for your needs.
But like every other person answering this question, I would strongly suggest making a case to the DBA to make the column a CLOB. From the program perspective this will be a BLOB and therefore simple to manage.
You said no BLOB or LONG... but what about CLOB? 4GB character data.
BLOB is the best solution. Anything else will be less convenient and a bigger maintenance annoyance.
Is BFILE a viable alternative datatype for your DBAs?
I don't get it. A CLOB is the appropriate database datatype. If your weird programming language will deal with strings of 8000 (or whatever) characters, what stops it writing those to a CLOB.
More specifically, what error do you get (from Oracle or your programming language) when you try to insert an 8000 character string into a column defined as a CLOB.