valOracle使用currval函数获取序列的当前值（oracle curr）

ValOracle: Using currval function to get the current value of a sequence

Oracle database users often require a unique identifier for their records. One common way to create this is through the use of a sequence, which generates unique numbers in ascending order. Sequences are easy to set up and use, but there are times when users need to access the current value of the sequence. This is where the currval function comes in.

The currval function allows users to obtn the current value of a sequence without incrementing it. This is useful when you need to obtn the current value for a specific record, for example, instead of the next value. The currval function is used in conjunction with the sequence’s nextval function, which returns the next value in the sequence.

Here is an example:

CREATE SEQUENCE my_seq START WITH 1 INCREMENT BY 1;

This sequence is created with a starting value of 1 and an increment of 1. To obtn the current value of the sequence, we use the currval function:

SELECT my_seq.currval FROM dual;

The dual table is used because the currval function must be called in a SELECT statement. The above query will return the current value of the sequence, which in this case is 1.

To obtn the next value in the sequence, we use the nextval function:

SELECT my_seq.nextval FROM dual;

This will return the next value in the sequence, which in this case is 2.

Here is an example of how you might use the currval function in a table insert:

INSERT INTO my_table (id, name, address)

VALUES (my_seq.currval, ‘John Doe’, ‘123 Mn St.’);

This inserts a new record into my_table with a unique identifier obtned from the currval function.

In conclusion, the currval function is an essential tool for Oracle users who need to access the current value of a sequence without incrementing it. It is easy to use and is ideal for obtning unique identifiers for records in a table. Using the currval function in tandem with the nextval function makes it easy to manage sequences and to ensure that they generate unique values for each record in a table.