But if many users tried to get a sequence
number at the same time, they might all read the ???last??? sequence number before the
new ???last??? sequence number had been written back. You could lock the row in the
table with the column containing the sequence number, but this would cause delays
as other users waited on locks. What??™s the solution? Create a sequence.
Oracle Database 11g allows the use of sequences within PL/SQL expressions.
Synonyms
All data structures within an Oracle database are stored within a specific schema. A
schema is associated with a particular username, and all objects are referenced with
the name of the schema followed by the name of the object.
For instance, if there were a table named EMP in a schema named DEMO, the table
would be referenced with the complete name of DEMO.EMP. If you don??™t supply a
specific schema name, Oracle assumes that the structure is in the schema for your
current username.
Schemas are a nice feature because object names have to be unique only within their
own schemas, but the qualified names for objects can get confusing, especially for end
users.
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