If you are interested in all sequences created in Oracle or in sequences of a particular user you may use service Oracle table ALL_SEQUENCES that contains all the information above and the name of the user who own a sequence.

Altering sequences

ALTER SEQUENCE [schema.]sequence_name
  [ INCREMENT BY integer_value ]
  [ MAXVALUE integer_value | NOMAXVALUE ]
  [ minvalue integer_value | nominvalue ]
  [ CYCLE | NOCYCLE ]
  [ CACHE integer_value | NOCACHE]
  [ ORDER | NOORDER ];

Here is an example:

CREATE SEQUENCE TestSeq;
ALTER SEQUENCE TestSeq MAXVALUE 9999 CYCLE;

Synonyms.

• public - available for all users
• private - available only to the owner or to the accounts to whom the privileges on the underlying objects are granted.

To create a synonym we use the CREATE SYNONYM statement. Here is the syntax

CREATE [PUBLIC] SYNONYM synonym_name
   FOR [schema.]object[@db_link];

CREATE PUBLIC SYNONYM employees FOR ist466.employees;

To remove a synonym use the DROP SYNONYM statement:

DROP [ PUBLIC ] SYNONYM synonym_name;

Use the keyword PUBLIC to remove public synonyms.

When a code references an unqualified table, view, procedure, function, or package, Oracle resolves the object references in this order:

1. An object owned by the current user.
2. A private synonyms own by the current user.
3. A public synonym.

SELECT *
  FROM employees;

Indexes.

Oracle usually retrieves rows from a table in only one of two ways:

• by ROWID
• by full-table scan.

B-tree indexes are the most common index type (this is the default type). These indexes can be either UNIQUE or nonunique and either simple (one column) or concatenated (multiple columns). These indexes provide the best performance on high-cardinality columns (columns that have many distinct values). B-tree indexes offer an efficient method to retrieve a small number of interesting rows. However, if more than about 5 percent of the table must be examined, a full-table scan is the preferred method.

B-tree indexes are beneficial only if a small percentage of a table is expected to be returned in query results. Because having an index requires that Oracle first examine the index to identify records that meet the criteria and then to retrieve the rows from the actual tables, large result sets require Oracle to do additional work. Basically, a large result set requires Oracle to scan the full table. The general rule is

Bitmap indexes are primarily used for decision-support systems or static data, because they do not support row-level locking. Like B-tree indexes bitmap indexes can be simple (one column) or concatenated (multiple columns), but in practice, bitmap indexes are almost always simple. Bitmap indexes are best used for low- to medium-cardinality columns, where multiple bitmap indexes can be combined with AND and OR conditions. Each key value has a bitmap, which contains a TRUE, FALSE, or NULL value for every row in the table.

For example, the bitmap indexes for the column sex and marital_status in the employees table will look like

ROWID	Gender	Mar.Status	Thus, if we execute the query SELECT fname, lname FROM employees WHERE sex = 'F' AND mar_status = 'married'; we are interested only in the rows that have 1 in both bitmap indexes. If we have these two bitmap indexes, Oracle doesn't have to scan the entire table. It's enough to read the two index tables and find the addressed of the rows we are interested in.
AAAHtZAAIAAAAUaAAA	0	1
AAAHtZAAIAAAAUaAAB	0	0
AAAHtZAAIAAAAUaAAC	1	1
AAAHtZAAIAAAAUaAAD	0	1
AAAHtZAAIAAAAUaAAE	1
AAAHtZAAIAAAAUaAAF	1
AAAHtZAAIAAAAUaAAG	1	0
AAAHtZAAIAAAAUaAAH	1	0
AAAHtZAAIAAAAUaAAI	0	1
AAAHtZAAIAAAAUaAAJ	1	0
AAAHtZAAIAAAAUaAAK	0
AAAHtZAAIAAAAUaAAL	0	1
AAAHtZAAIAAAAUaAAM	0	0
AAAHtZAAIAAAAUaAAN	0	1
AAAHtZAAIAAAAUaAAO	1	1
AAAHtZAAIAAAAUaAAP	0	0
AAAHtZAAIAAAAUaAAQ	1	0
AAAHtZAAIAAAAUaAAR	0	0
AAAHtZAAIAAAAUaAAS	0	0
AAAHtZAAIAAAAUaAAT	1	1
AAAHtZAAIAAAAUaAAU	0	0
AAAHtZAAIAAAAUaAAV	1
AAAHtZAAIAAAAUaAAW	0	0
AAAHtZAAIAAAAUaAAX	0	0
AAAHtZAAIAAAAUaAAY	1	0
AAAHtZAAIAAAAUaAAZ	1
AAAHtZAAIAAAAUaAAa	1	0

Creating indexes

CREATE [ UNIQUE | BITMAP ] INDEX index_name
  ON [schema.]table_name ( index_expression_list );

CREATE BITMAP INDEX employees_sex_indx ON employees (sex);
CREATE INDEX employees_fullname_indx
  ON employees ( CONCAT(lname,fname) );
CREATE UNIQUE INDEX employees_name_phone_indx
  ON employees ( lname, phone );

• The table is large and a particular column is frequently used in WHERE clause.
• The column tends to contain a large number of NULL values because the index can identify rows that contain values in that column and those that do not.
• In some cases, an index might be appropriate for conditions based on a calculated value because the condition being referenced is already identified in the index as "converted" (or derived) state.

SELECT index_name "Index", index_type "Type",
       table_owner ||'.'|| table_name "Table",
       table_type "Type", uniqueness
  FROM user_indexes;

To remove an index, use DROP INDEX stateement

DROP INDEX index_name;