/SQL/Mysql bidirectional composite primary key

Mysql bidirectional composite primary key

create trigger bi_foo before insert on foo
for each row
begin
  if exists(select 1 from foo where bar1 = NEW.bar2 and bar2 = NEW.bar1)
  then
    signal sqlstate '50000' set message_text="Oops";
  end if;
end

Source: stackoverflow.com

Mysql bidirectional composite primary key

CREATE TRIGGER uinsert BEFORE INSERT ON tbl_challenger
 FOR EACH ROW SET NEW.u0 = LEAST(NEW.host,NEW.challenger),
  NEW.u1 = GREATEST(NEW.host,NEW.challenger);
#same for update
CREATE UNIQUE INDEX uniqueness ON tbl_challenger(u0,u1);

Source: stackoverflow.com

Similar codes

0 vote165 views1 answer
Finding leap year in sql
SQL
3 votes144 views2 answers
Having in mysql
SQL
3 votes138 views4 answers
Mysql decimal
SQL
0 vote185 views2 answers
Cascade syntax in sql
SQL
2 votes145 views2 answers
Select list is not in group by clause
SQL
0 vote129 views1 answer
Selecting Data in SQL - Select Data
SQL
13 votes138 views2 answers
Sqlite rename column
SQL
0 vote152 views1 answer
Make parameters nullable in sql server
SQL
1 vote152 views3 answers
How to truncate table with foreign key constraint
SQL
3 votes137 views4 answers
Stop MySQL
SQL