sequence.CURRVAL
sequence.NEXTVAL

schema.sequence.CURRVAL
schema.sequence.NEXTVAL

schema.sequence.CURRVAL@dblink
schema.sequence.NEXTVAL@dblink

Where to Use Sequence Values

You can use CURRVAL and NEXTVAL in the following locations:

• The select list of a SELECT statement that is not contained in a subquery, materialized view, or view

• The select list of a subquery in an INSERT statement

• The VALUES clause of an INSERT statement

• The SET clause of an UPDATE statement

Restrictions on Sequence Values

You cannot use CURRVAL and NEXTVAL in the following constructs:

• A subquery in a DELETE, SELECT, or UPDATE statement

• A query of a view or of a materialized view

• A SELECT statement with the DISTINCT operator

• A SELECT statement with a GROUP BY clause or ORDER BY clause

• A SELECT statement that is combined with another SELECT statement with the UNION, INTERSECT, or MINUS set operator

• The WHERE clause of a SELECT statement

• The DEFAULT value of a column in a CREATE TABLE or ALTER TABLE statement

• The condition of a CHECK constraint

Within a single SQL statement that uses CURRVAL or NEXTVAL, all referenced LONG columns, updated tables, and locked tables must be located on the same database.

How to Use Sequence Values

When you create a sequence, you can define its initial value and the increment between its values. The first reference to NEXTVAL returns the initial value of the sequence. Subsequent references to NEXTVAL increment the sequence value by the defined increment and return the new value. Any reference to CURRVAL always returns the current value of the sequence, which is the value returned by the last reference to NEXTVAL.

Before you use CURRVAL for a sequence in your session, you must first initialize the sequence with NEXTVAL. Please refer to CREATE SEQUENCE for information on sequences.

Within a single SQL statement containing a reference to NEXTVAL, Oracle increments the sequence only once:

• For each row returned by the outer query block of a SELECT statement. Such a query block can appear in the following places:

• A top-level SELECT statement

• An INSERT ... SELECT statement (either single-table or multitable). For a multitable insert, the reference to NEXTVAL must appear in the VALUES clause, and the sequence is updated once for each row returned by the subquery, even though NEXTVAL may be referenced in multiple branches of the multitable insert.

• A CREATE TABLE ... AS SELECT statement

• A CREATE MATERIALIZED VIEW ... AS SELECT statement

• For each row updated in an UPDATE statement

• For each INSERT statement containing a VALUES clause

• For each row either inserted or updated in a MERGE statement. The reference to NEXTVAL can appear in the merge_insert_clause or the merge_update_clause.

If any of these locations contains more than one reference to NEXTVAL, then Oracle increments the sequence once and returns the same value for all occurrences of NEXTVAL.

If any of these locations contains references to both CURRVAL and NEXTVAL, then Oracle increments the sequence and returns the same value for both CURRVAL and NEXTVAL.

A sequence can be accessed by many users concurrently with no waiting or locking.

Finding the next value of a sequence: Example

This example selects the next value of the employee sequence in the sample schema hr:

SELECT employees_seq.nextval 
    FROM DUAL;

Inserting sequence values into a table: Example

This example increments the employee sequence and uses its value for a new employee inserted into the sample table hr.employees:

INSERT INTO employees
   VALUES (employees_seq.nextval, 'John', 'Doe', 'jdoe', 
   '555-1212', TO_DATE(SYSDATE), 'PU_CLERK', 2500, null, null,
   30);

Reusing the current value of a sequence: Example

This example adds a new order with the next order number to the master order table. It then adds suborders with this number to the detail order table:

INSERT INTO orders (order_id, order_date, customer_id)
   VALUES (orders_seq.nextval, TO_DATE(SYSDATE), 106);

INSERT INTO order_items (order_id, line_item_id, product_id)
   VALUES (orders_seq.currval, 1, 2359);

INSERT INTO order_items (order_id, line_item_id, product_id)
   VALUES (orders_seq.currval, 2, 3290);

INSERT INTO order_items (order_id, line_item_id, product_id)
   VALUES (orders_seq.currval, 3, 2381);