Detailed explanation of Oracle serial number query method-Mysql Tutorial-php.cn

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 theUSER_SEQUENCESsystem view or theDBA_SEQUENCESview. The following are the steps to query serial numbers through SQL statements:

Query the sequence information owned by the current user:
```
SELECT sequence_name, min_value, max_value, increment_by, last_number FROM user_sequences;
```
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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.
Query the current value of the specified sequence:
```
SELECT last_number FROM user_sequences WHERE sequence_name = 'SEQ_NAME';
```
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ReplaceSEQ_NAMEwith 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:

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;
```
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This PL/SQL code will query the name The next value in the sequence ofSEQ_NAMEand outputs the result to the console.

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;

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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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