What is the equivalent of varchar(max) in Oracle?

Question

What is the equivalent of varchar(max) in Oracle?

CLOB?

Answer 1

Varchars are limited to 4000 characters in Oracle. Other than that, you have to use a LONG or a CLOB. Prefer CLOBs. LONGs are the older equivalent.

From this Oracle documentation:

LOBs vs. LONG and LONG RAW

LOBs are different from the older LONG and LONG RAW datatypes in many ways.

• The maximum size of a LOB is 4 Gigabytes versus 2 Gigabytes for LONG and LONG RAW.
• You can use random as well as sequential access methods on LOBs; you can only use sequential access methods on LONG and LONG RAW.
• LOBs (except NCLOBs) can be attributes of an object type that you define.
• Tables can have multiple LOB columns, but can have only one LONG or LONG RAW column.

Migration of existing LONG and LONG Raw attributes to LOBs is recommended by Oracle. Oracle plans to end support of LONG and LONG RAW in future releases. See Oracle8 Migration for more information on migration.

Answer 2

In PL/SQL, VARCHAR2 can be up to 32767 bytes. For SQL the limit is 4000 bytes (which may be less than 4000 characters if you are using a multi-byte character set).

Answer 3

As I understand it, a VARCHAR(MAX) data type is a SQL Server 2005 specific way of specifying a text field that can either be small (up to 8000 characters in SQL Server) or big (up to 2GB in SQL Server). The database handles the change in storage behind the scenes as the content grows from the small range to the large range.

There is no equivalent in Oracle.

You either have a smallish bit of text in a VARCHAR2 - which is up to 32767 bytes in pl/sql and up to 4000 bytes in SQL (i.e. in a table definition) - or you have a potentially very big bit of text in a CLOB (which is a specialised BLOB).

Answer 4

AFAIK, there is no equivalent. The closest you get in ORACLE is the CLOB, which has the same limitations that TEXT had in SQL Server back in the 'bad old days'.

Answer 5

An approach I have used in the past (MS SQL, prior to Varchar(max)):

Put two columns in the table, one smallish Varchar (255, for example), and another Text. Then build your application so that it will use the Varchar column for small data, leaving the Text null. If the data is larger than the Varchar, leave that null and store it in the Text. This way, small data doesn't take up its own page on the server. The tradeoff here is that all applications using the data have to agree to this scheme, and have logic to account for it. But it works well.

I presume the same is true in Oracle, just substiture Varchar2 for Varchar, and CLOB for Text. I don't pretend to know what the right size for the varchar should be - that's data dependent, and also depends on the rest of the columns in the table.