Mysql - second auto_increment col with diff behaviour
I have a proposals table like this
- ID (auto_increment) - proposal_id - c开发者_开发技巧lient_idThere a way in sql that the proposal_id increments just for each client_id
example:
ID proposal_id client_id
1 1 1 2 1 2 3 2 1 4 3 1 5 2 2 6 3 2i know i can get the last poposal_id and +1 and i add the new entry... but i dont want to do a sql instruction just to get this value... instead i want to use in a sql!
Tkz Roberto
As I understand you wish to have proposal_id as a sequence in a continuos manner per client_id. Either you should normalize the table to split into per-client-table [tricky and not advisable] to do this or write a SELECT
I think this is what you want if using innodb (recommended) although you can simplify this with myisam
delimiter ;
drop table if exists customer;
create table customer(
cust_id int unsigned not null auto_increment primary key,
name varchar(255) unique not null,
next_proposal_id smallint unsigned not null default 0
)engine = innodb;
insert into customer (name) values ('c1'),('c2'),('c3');
drop table if exists proposal;
create table proposal(
cust_id int unsigned not null,
proposal_id smallint unsigned not null,
proposal_date datetime not null,
primary key (cust_id, proposal_id) -- composite clustered primary key
)engine=innodb;
delimiter #
create trigger proposal_before_ins_trig before insert on proposal for each row
begin
declare new_proposal_id smallint unsigned default 0;
select next_proposal_id+1 into new_proposal_id from customer
where cust_id = new.cust_id;
update customer set next_proposal_id = new_proposal_id where cust_id = new.cust_id;
set new.proposal_id = new_proposal_id;
set new.proposal_date = now();
end#
delimiter ;
insert into proposal (cust_id) values (1),(2),(1),(3),(2),(1),(1),(2);
select * from proposal;
select * from customer;
hope it helps :)
i've added the myisam version below for good measure:
drop table if exists customer;
create table customer(
cust_id int unsigned not null auto_increment primary key,
name varchar(255) unique not null
)engine = myisam;
insert into customer (name) values ('c1'),('c2'),('c3');
drop table if exists proposal;
create table proposal(
cust_id int unsigned not null,
proposal_id smallint unsigned not null auto_increment,
proposal_date datetime not null,
primary key (cust_id, proposal_id) -- composite non clustered primary key
)engine=myisam;
insert into proposal (cust_id,proposal_date) values
(1,now()),(2,now()),(1,now()),(3,now()),(2,now()),(1,now()),(1,now()),(2,now());
select * from customer;
select * from proposal order by cust_id;
I think that you could design a complicated enough query to take care of this without any non-sql code, but that's not in the spirit of what you're asking. There is not a way to create the type of field-specific increment that you're asking for as a specification of the table itself.
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