How to set id self-growth of PostgreSQL tables

For an existing PostgreSQL table, to set the ID field to autoincrement, you can follow the following steps:

Create a sequence:

First, you need to create a sequence that will be used to generate the autoincremental ID. The following SQL statements can be used to create a sequence:

CREATE SEQUENCE your_table_id_seq
  START WITH 1
  INCREMENT BY 1;

here,your_table_id_seqis the name of the sequence.START WITH 1Indicates that the sequence starts from 1,INCREMENT BY 1Indicates that 1[^4^] is added each time.

Set the default value:

Next, you need to associate the sequence with the ID field in the table. This can be achieved by setting the default value of the field to the next value of the sequence:

ALTER TABLE your_table
ALTER COLUMN id SET DEFAULT nextval('your_table_id_seq');

Note that if the data type of your ID field does not match the data type of the sequence, you need to modify the data type of the ID field to make sure they are consistent [^4^].

Modify the table structure (if required):

If your table does not have a corresponding autoincrement field, you need to add one first:

ALTER TABLE your_table
ADD COLUMN id SERIAL PRIMARY KEY;

SERIALis a special type in PostgreSQL, which is actuallyINTalias for , with a sequence created automatically. If you need a different integer type, you can useSMALLSERIALorBIGSERIALWait [^1^].

Reset the sequence (if required):

If you want to reset the start value of the sequence, you can use the following command:

SELECT setval('your_table_id_seq', (SELECT MAX(id) + 1 FROM your_table), false);

This sets the next value of the sequence to the current maximum ID value in the table plus 1[^8^].

Through the above steps, you can set the ID field to auto-increment for the existing PostgreSQL table.

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