oracle query sequence

In Oracle database, a sequence is an object that can be used to generate unique integer values. It is often used as a primary key or other data items that need to be uniquely identified. When using sequences, the most common operation is to get the next sequence value. This article explains how to query Oracle sequences.

1. View the current sequence value

Querying the value of the current sequence is very simple, just execute the following SQL statement:

SELECT 序列名.CURRVAL FROM DUAL;

where "sequence name" " is the name of the sequence you want to query. It should be noted here that the value of the current sequence can only be queried after the sequence has been used (such as assigned to a column in a table). If not used, CURRVAL will throw an exception.

2. Query the next sequence value

To query the next available sequence value, you need to call the NEXTVAL attribute of the sequence. Just execute the following SQL statement:

SELECT 序列名.NEXTVAL FROM DUAL;

This statement will return the next value of the sequence and increase the current value of the sequence by 1. Because NEXTVAL automatically increments the current value of the sequence, NEXTVAL must be called before using the sequence, otherwise an exception will be thrown.

3. Modify the current value of the sequence

If you need to modify the current value of the sequence, you can use the ALTER SEQUENCE command. Just execute the following SQL statement:

ALTER SEQUENCE 序列名 RESTART WITH 新值;

This statement will reset the current value of the sequence to the specified new value. It should be noted that modifying the current value may cause the value generated by the sequence to be a duplicate of the previous value, so it must be used with caution.

4. View the definition of a sequence

To view the definition of a sequence (such as the starting value, step size and other information of the sequence), you can execute the following SQL command:

SELECT * FROM USER_SEQUENCES WHERE SEQUENCE_NAME = '序列名';

This command will return a result set containing sequence definition information. In the query results, you can view information such as the current value, next value, and step size of the sequence.

Summary

Querying sequences in Oracle database is a very important operation. By understanding the basic usage of sequences, you can quickly query the current value, next value of the sequence, and the definition information of the sequence. Mastering these skills can help you better understand and use Oracle sequences.

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