mysql - Issue with adding Foreign Key Constraint -


i have built following tables in mysql using v.5.6.18. tried create table foreign key constraint didn't work. trying alter. looks far:

create table campaign_overviews(     -> campaign varchar(45),     -> petition varchar(45),     -> datestarted date,     -> primary key(campaign,petition,datestarted); error 1046 (3d000): no database selected mysql> use reclaimemailacq; database changed mysql> create table campaign_overviews(     -> campaign varchar(45),     -> petition varchar(45),     -> datestarted date,     -> primary key(campaign,petition,datestarted); error 1064 (42000): have error in sql syntax; check manual corresponds mysql server version right syntax use near '' @ line 5 mysql> create table campaign_overviews(     -> campaign varchar(45) not null,     -> petition varchar(45) not null,     -> datestarted date not null,     -> primary key(campaign, petition, datestarted)     -> ); query ok, 0 rows affected (0.04 sec)  mysql> create table petitions(     -> petition varchar(45) not null,     -> medium varchar(45),     -> adid varchar(45) not null,     -> url varchar(45),     -> cost float,     -> primary key(adid)     -> ); query ok, 0 rows affected (0.03 sec)  mysql> create table email_addresses(     -> email varchar(45) not null,     -> date_acquired datetime,     -> petition varchar(45),     -> adid varchar(45) not null,     -> primary key (email, adid)     -> ); query ok, 0 rows affected (0.04 sec)  mysql> alter table petitions     -> add foreign key (petition)     -> references campaign_overviews (petition); error 1215 (hy000): cannot add foreign key constraint mysql> show tables; +---------------------------+ | tables_in_reclaimemailacq | +---------------------------+ | campaign_overviews        | | email_addresses           | | petitions                 | +---------------------------+ 3 rows in set (0.00 sec)  mysql> describe campaign_overviews; +-------------+-------------+------+-----+---------+-------+ | field       | type        | null | key | default | | +-------------+-------------+------+-----+---------+-------+ | campaign    | varchar(45) | no   | pri | null    |       | | petition    | varchar(45) | no   | pri | null    |       | | datestarted | date        | no   | pri | null    |       | +-------------+-------------+------+-----+---------+-------+ 3 rows in set (0.01 sec)  mysql> describe email_addresses; +---------------+-------------+------+-----+---------+-------+ | field         | type        | null | key | default | | +---------------+-------------+------+-----+---------+-------+ | email         | varchar(45) | no   | pri | null    |       | | date_acquired | datetime    | yes  |     | null    |       | | petition      | varchar(45) | yes  |     | null    |       | | adid          | varchar(45) | no   | pri | null    |       | +---------------+-------------+------+-----+---------+-------+ 4 rows in set (0.01 sec)  describe petitions; +----------+-------------+------+-----+---------+-------+ | field    | type        | null | key | default | | +----------+-------------+------+-----+---------+-------+ | petition | varchar(45) | no   |     | null    |       | | medium   | varchar(45) | yes  |     | null    |       | | adid     | varchar(45) | no   | pri | null    |       | | url      | varchar(45) | yes  |     | null    |       | | cost     | float       | yes  |     | null    |       | +----------+-------------+------+-----+---------+-------+ 5 rows in set (0.01 sec) 

you have foreign key in wrong table. foreign key should exist in referencing table (many) , should reference referenced (one) table. should be:

alter table campaign_overviews add foreign key (petition) references petitions (petition); 

also need index (key) on field in petition table.

alter table petition add key petition (petition); 

for reference: http://dev.mysql.com/doc/refman/5.6/en/create-table-foreign-keys.html


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