The application of Nextval,currval in the database.

X.nextval gets the next sequence value of the x sequence, X.currval gets the current sequence value of the x sequence.

Note: In reference to X. You must first refer to xbefore currval . Nextval, otherwise the ORA-08002 is reported: The sequence X.currval has not yet been defined in this session.

Specific applications

1. Create a sequence:

Create sequence Test_seq increment by 1 start with 1 maxvalue minvalue 0 nocycle cache order;

Select Sequence Test_seq.nextval from dual;//once per call nextval, sequence values are incremented one time (increment value custom)

Select sequence Test_seq.currval from dual;

2. Create a table:

CREATE TABLE test (col1 int, col2 int);

3. Insert Record:

INSERT into test values (0, 0);

4, the use of Nextval

INSERT into Test (col1, col2) VALUES (Test_seq.nextval, test_seq.nextval);//Do you guess col1 and col2 values will be the same?

If the test table has two records with a col1 value of 2, then:

Update Test Set col2 = test_seq.nextval where col1 = 2;//Do you guess the col2 value will be the same after the update?

The application of Nextval,currval in the database.