Detailed introduction to Oracle's method of querying serial numbers

Oracle is a very powerful database management system that is widely used in various large-scale enterprise applications. In Oracle database, sequence number (sequence) is a very useful object that can be used to generate unique numeric identifiers. This article will introduce in detail Oracle's method of querying serial numbers.

A serial number is an object in Oracle that can generate a unique numeric identifier. Serial numbers are often used to generate primary key values ​​and can be shared between multiple tables. To create a sequence number object, you can use the following syntax:

CREATE SEQUENCE sequence_name
START WITH start_value
INCREMENT BY increment_value
MAXVALUE max_value
MINVALUE min_value
CYCLE/NOCYCLE
CACHE cache_value;

Among them, sequence_name is the name of the sequence number, start_value is the initial value of the sequence number, increment_value is the increment of the sequence number, max_value is the maximum value of the sequence number Value, min_value is the minimum value of the serial number, cycle/nocycle indicates whether the serial number is recycled, cache_value is the cache size of the serial number.

Once the serial number object is created, we can use it to generate a unique numeric identifier. The way to generate numeric identifiers is to use Oracle's NEXTVAL function. This function returns the next value of the sequence number and increments the current value of the sequence number by increment_value. As shown below:

SELECT sequence_name.NEXTVAL FROM dual;

Among them, sequence_name is the name of the sequence number, dual is a virtual table in Oracle, used to return the query results of a single row.

To demonstrate how to use the serial number object, we can create a simple example table and use the serial number as the primary key. The following is the SQL statement to create the sample table and serial number object:

CREATE TABLE example_table (
    id NUMBER(10) PRIMARY KEY,
    name VARCHAR2(50) NOT NULL
);

CREATE SEQUENCE example_seq
START WITH 1
INCREMENT BY 1
NO CYCLE
CACHE 20;

Then, we can insert some data into the sample table and use the serial number as the primary key. As shown below:

INSERT INTO example_table VALUES (example_seq.NEXTVAL, 'A');
INSERT INTO example_table VALUES (example_seq.NEXTVAL, 'B');
INSERT INTO example_table VALUES (example_seq.NEXTVAL, 'C');

Next, we can query the data in the example table to confirm that the serial number has correctly generated a unique primary key value:

SELECT * FROM example_table;

ID  NAME
--  ----
1   A
2   B
3   C

Using the serial number object can Generate unique numeric identifiers very conveniently. In addition, the serial number object can also use Oracle's CURRVAL function to obtain the value of the current serial number, and use Oracle's ALTER SEQUENCE statement to change the value of the serial number.

In general, querying serial numbers in Oracle is very simple. Just use the CREATE SEQUENCE statement to create a sequence number object, and then use the NEXTVAL function to generate a unique numeric identifier. In scenarios where unique identifiers are required, serial numbers are a very useful tool that can help us better manage data.

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