Detailed explanation of Oracle serial number query method

Detailed explanation of Oracle serial number query method

In Oracle database, sequence is used to generate a unique object that increases or decreases numbers. It is often used to generate unique objects for the primary key of a table. value. When performing database operations, sometimes you need to query the current value or next value of a sequence. This article will introduce in detail the method of Oracle serial number query, including through SQL statements and PL/SQL code examples.

Query the serial number through SQL statements

To query the serial number through SQL statements, you can use the USER_SEQUENCES system view or the DBA_SEQUENCES view. The following are the steps to query serial numbers through SQL statements:

1. Query the sequence information owned by the current user:

   SELECT sequence_name, min_value, max_value, increment_by, last_number
   FROM user_sequences;

   This SQL statement will return the names of all sequences owned by the current user , minimum value, maximum value, increment and the last generated sequence number.

2. Query the current value of the specified sequence:

   SELECT last_number
   FROM user_sequences
   WHERE sequence_name = 'SEQ_NAME';

   Replace SEQ_NAME with the name of the sequence you want to query. Execute the SQL statement to get the specified The current value of the sequence.

Query the serial number through PL/SQL code

In addition to using SQL statements, you can also query the serial number through PL/SQL code. The following is an example of querying a serial number through PL/SQL code:

1. Query the next value of the specified sequence:

   DECLARE
    next_val NUMBER;
   BEGIN
    SELECT SEQ_NAME.NEXTVAL
    INTO next_val
    FROM dual;
    DBMS_OUTPUT.PUT_LINE('Next value of SEQ_NAME is ' || next_val);
   END;

   This PL/SQL code will query the name The next value in the sequence of SEQ_NAME and outputs the result to the console.

2. Query the current values ​​of all sequences:

   DECLARE
    seq_name VARCHAR2(100);
    last_num NUMBER;
   BEGIN
    FOR seq_rec IN (SELECT sequence_name FROM user_sequences) LOOP
        seq_name := seq_rec.sequence_name;
        EXECUTE IMMEDIATE 'SELECT ' || seq_name || '.last_number FROM dual' INTO last_num;
        DBMS_OUTPUT.PUT_LINE('Current value of ' || seq_name || ' is ' || last_num);
    END LOOP;
   END;

   This PL/SQL code traverses all sequences of the current user, queries their current values ​​and outputs them to the console.

Through the above SQL statements and PL/SQL code examples, you can flexibly query serial number information in the Oracle database to facilitate database management and development operations.

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