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Possible to do a MySQL foreign key to one of two possible tables?
...signate which target table is referenced.
CREATE TABLE popular_places (
user_id INT NOT NULL,
place_id INT NOT NULL,
place_type VARCHAR(10) -- either 'states' or 'countries'
-- foreign key is not possible
);
There's no way to model Polymorphic Associations using SQL constraints. A foreig...
What is the difference between a stored procedure and a view?
...hen and why to use each.
Say I have two tables:
tbl_user, with columns: user_id, user_name, user_pw
tbl_profile, with columns: profile_id, user_id, profile_description
So, if I find myself querying from those tables A LOT... instead of doing the join in EVERY piece of SQL, I would define a view...
Rails has_and_belongs_to_many migration
...
You need to add a separate join table with only a restaurant_id and user_id (no primary key), in alphabetical order.
First run your migrations, then edit the generated migration file.
Rails 3
rails g migration create_restaurants_users_table
Rails 4:
rails g migration create_restaurants...
How to implement a unique index on two columns in rails
...
add_index :subscriptions, [:user_id, :content_id], unique: true
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When should I use a composite index?
...To create a friends' tables (i.e. for a social network) we need 2 columns: user_id, friend_id.
Table Strcture
user_id (medium_int)
friend_id (medium_int)
Primary Key -> (user_id, friend_id)
By virtue, a Primary Key (PK) is unique and by creating a composite PK, Innodb will automatically chec...
What is a proper naming convention for MySQL FKs?
...d table name]_[referencing field name]
Example:
CREATE TABLE users(
user_id int,
name varchar(100)
);
CREATE TABLE messages(
message_id int,
user_id int
);
ALTER TABLE messages ADD CONSTRAINT fk_messages_users_user_id
FOREIGN KEY (user_id) REFERENCES users(user_...
Mail multipart/alternative vs multipart/mixed
...MessageInternal(service, "me", message1)
def SendMessageInternal(service, user_id, message):
try:
message = (service.users().messages().send(userId=user_id, body=message).execute())
print 'Message Id: %s' % message['id']
return message
except errors.HttpError, error:...
Insert auto increment primary key to existing table
...mposite primary key using the following code:
DROP TABLE IF EXISTS SAKAI_USER_ID_MAP;
CREATE TABLE SAKAI_USER_ID_MAP (
USER_ID VARCHAR (99) NOT NULL,
EID VARCHAR (255) NOT NULL,
PRIMARY KEY (USER_ID)
);
INSERT INTO SAKAI_USER_ID_MAP VALUES ('admin...
MySQL Insert into multiple tables? (Database normalization?)
...00.com');
full script:
drop table if exists users;
create table users
(
user_id int unsigned not null auto_increment primary key,
username varchar(32) unique not null
)
engine=innodb;
drop table if exists user_profile;
create table user_profile
(
profile_id int unsigned not null auto_increment p...
How to change the foreign key referential action? (behavior)
...e refers to Users table:
mysql> SHOW CREATE TABLE UserDetails;
:
:
`User_id` int(11) DEFAULT NULL,
PRIMARY KEY (`Detail_id`),
KEY `FK_User_id` (`User_id`),
CONSTRAINT `FK_User_id` FOREIGN KEY (`User_id`) REFERENCES `Users` (`User_id`)
:
:
First step:
mysql> ALTER TABLE `UserDeta...