Restrictions using LOBs
With a few exceptions, you can use LOBs in the same contexts in which you can use other varying-length strings.
The following table shows the contexts in which LOBs cannot be used.
Context of usage | LOB (CLOB, DBCLOB, or BLOB) |
---|---|
A GROUP BY clause | Not allowed |
An ORDER BY clause | Not allowed |
A CREATE INDEX statement that creates an index using an expression | Not allowed except when the index is created using an expression, in which case an inline LOB column can be referenced as the source data type for the SUBSTR and SUBSTRING built-in functions. |
A SELECT DISTINCT statement | Not allowed |
A MERGE statement | Cannot be used in the context of an INCLUDE column-name clause |
A subselect of a set operation except UNION ALL | Not allowed |
Predicates | Cannot be used in any predicate except EXISTS, LIKE, and NULL. This restriction includes a simple-when-clause in a CASE expression. expression WHEN expression in a simple-when-clause is equivalent to a predicate with expression=expression. |
The definition of primary, unique, and foreign keys | Not allowed |
Check constraints | Not allowed |