postgresql 在 CONFLICT 更新上使用 insert 进行流 no

Question

can I generate serial number use insert conflict not need SEQUENCE ?

this my table :

 CREATE TABLE web.flow_no
(
    apply_kind character varying(15) COLLATE pg_catalog."default" NOT NULL,
    seq_name character varying(10) COLLATE pg_catalog."default" NOT NULL,
    seq_no numeric(8,0) NOT NULL DEFAULT 1,
    CONSTRAINT flow_no_pk PRIMARY KEY (apply_kind, seq_name)       
)

but Sql is not OK: 1:

insert into web.flow_no(apply_kind,seq_name)values('ISO_FILE','202003')
ON CONFLICT(apply_kind, seq_name)
DO UPDATE SET seq_no=EXCLUDED.seq_no+1
 RETURNING seq_no

is alway get 2

2:

insert into web.flow_no(apply_kind,seq_name)values('ISO_FILE','202003')
ON CONFLICT(apply_kind, seq_name)
DO UPDATE SET seq_no=
(select seq_no from  web.flow_no where apply_kind=EXCLUDED.apply_kind and 
 seq_name=EXCLUDED.seq_name)+1
 RETURNING seq_no

is not thread safe (ATOM): multiple query returning seq_no will conflict

Answer 1

If you want to increment seq for each insert conflict, then you should not use the EXCLUDED pseudo-table, which refers the row proposed for insertion. Instead, use the table name:

INSERT INTO web.flow_no(apply_kind,seq_name)values('ISO_FILE','202003')
ON CONFLICT(apply_kind, seq_name)
DO UPDATE SET seq_no = flow_no.seq_no + 1
RETURNING seq_no

Demo on DB Fiddle .