https://imgur.com/a/HAlSO7z
I am totally confused as to what I should identify as the primary key for the flatpack components table. For the flatpack components, there is a multiplicty relationship with both of the other tables, although intuitively I am leaning toward the component table because that seems more relevant, and the multiplicity is 0 to Many to 1, as opposed to the Many to 1 associated with flatpack components.
I have tried a composite key of both flatpackID and componentNo, but have ran into errors whilst trying to populate the table with sample data.
At present, I have the following tables:
CREATE TABLE `flatpack_apn` (
`flatpackid` INT(11) NOT NULL AUTO_INCREMENT,
`name` TINYTEXT NOT NULL,
`colour` TEXT NULL DEFAULT NULL,
`flatpacktype` ENUM('Office','Kitchen','Bedroom','General') NOT NULL,
`unitprice` DECIMAL(5,2) NULL DEFAULT NULL,
PRIMARY KEY (`flatpackid`)
)
COLLATE='hp8_english_ci'
ENGINE=InnoDB
AUTO_INCREMENT=2217
;
CREATE TABLE `component_apn` (
`componentno` INT(11) NOT NULL AUTO_INCREMENT,
`description` VARCHAR(30) NOT NULL,
PRIMARY KEY (`componentno`)
)
COLLATE='hp8_english_ci'
ENGINE=InnoDB
AUTO_INCREMENT=20
;
For the flatpackcomponents_apn table (the table in contention) I have tentatively put the following code:
CREATE TABLE `flatpackcomponents_apn` (
`flatpackid` INT(11) NOT NULL DEFAULT '12',
`componentno` INT(11) NOT NULL DEFAULT '23',
`quantity` INT(10) NOT NULL,
PRIMARY KEY (`componentno`, `flatpackid`),
INDEX `flatpackid` (`flatpackid`),
INDEX `componentno` (`componentno`),
CONSTRAINT `flatpackcomponents_apn_ibfk_1` FOREIGN KEY (`flatpackid`) REFERENCES `flatpack_apn` (`flatpackid`),
CONSTRAINT `flatpackcomponents_apn_ibfk_2` FOREIGN KEY (`componentno`) REFERENCES `component_apn` (`componentno`)
)
COLLATE='hp8_english_ci'
ENGINE=InnoDB
;
Related
I was referring these to Hibernate tuts: 1, 2.
I was not able to understand how one to one and one to many relationships are defined in MySQL tables.
This is SQL for one to many relationship:
CREATE TABLE `Cart` (
`cart_id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`total` decimal(10,0) NOT NULL,
`name` varchar(10) DEFAULT NULL,
PRIMARY KEY (`cart_id`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;
CREATE TABLE `Items` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`cart_id` int(11) unsigned NOT NULL,
`item_id` varchar(10) NOT NULL,
`item_total` decimal(10,0) NOT NULL,
`quantity` int(3) NOT NULL,
PRIMARY KEY (`id`),
KEY `cart_id` (`cart_id`),
CONSTRAINT `items_ibfk_1` FOREIGN KEY (`cart_id`) REFERENCES `Cart` (`cart_id`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8;
This is SQL for one to one relationship:
-- Create Transaction Table
CREATE TABLE `Transaction` (
`txn_id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`txn_date` date NOT NULL,
`txn_total` decimal(10,0) NOT NULL,
PRIMARY KEY (`txn_id`)
) ENGINE=InnoDB AUTO_INCREMENT=16 DEFAULT CHARSET=utf8;
-- Create Customer table
CREATE TABLE `Customer` (
`txn_id` int(11) unsigned NOT NULL,
`cust_name` varchar(20) NOT NULL DEFAULT '',
`cust_email` varchar(20) DEFAULT NULL,
`cust_address` varchar(50) NOT NULL DEFAULT '',
PRIMARY KEY (`txn_id`),
CONSTRAINT `customer_ibfk_1` FOREIGN KEY (`txn_id`) REFERENCES `Transaction` (`txn_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
If eyes are ok, I dont see any difference between two. Is it like this relationship cardinality constraints are implemented only at hibernate level and are not enforced by database? Or my eyes are missing something?
It's actually possible to define 1:1 relationships in SQL. There are two ways:
The child table has the same PK as the parent table, with the same values. This column is also an FK to the parent table.
The child table has a different PK. It also has a FK that points to the parent table, and this FK has a UNIQUE constraint.
If you noticed, in both cases the FK is UNIQUE (it's the PK, or has a UNIQUE constraint), and that's the key aspect. It's not possible the create a second row in the child table that has the same parent.
The case you included in your question opted for strategy #1.
I have following tables/CREATE sintaxis:
CREATE TABLE `users` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`parentId` int(10) unsigned DEFAULT NULL,
`fullName` varchar(50) COLLATE utf8_unicode_ci NOT NULL DEFAULT '',
`alias` varchar(35) COLLATE utf8_unicode_ci DEFAULT NULL,
`username` varchar(50) COLLATE utf8_unicode_ci NOT NULL DEFAULT '',
`password` varchar(255) COLLATE utf8_unicode_ci NOT NULL DEFAULT '',
PRIMARY KEY (`id`),
UNIQUE KEY `uk_username` (`username`),
UNIQUE KEY `uk_parentId_fullName_alias` (`parentId`,`fullName`,`alias`),
KEY `fk_users_parentId` (`parentId`),
CONSTRAINT `fk_users_parentId` FOREIGN KEY (`parentId`) REFERENCES `users` (`id`) ON DELETE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;
CREATE TABLE `userSettings` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`userId` int(11) unsigned NOT NULL,
`settingsArray` text NOT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `uk_userId` (`userId`),
KEY `fk_userSettings_userId` (`userId`),
CONSTRAINT `fk_userSettings_userId` FOREIGN KEY (`userId`) REFERENCES `users` (`id`) ON DELETE CASCADE
) ENGINE=MyISAM AUTO_INCREMENT=6 DEFAULT CHARSET=latin1
im trying to create one table with user data and another one with the user settings, when i create the userSettings table it doesnt create the foreign key, is there something wrong with the create sintaxis? It is related with creating two indexes for same column?
Here what i get after creating the userSettings table:
CREATE TABLE `userSettings` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`userId` int(11) unsigned NOT NULL,
`settingsArray` text NOT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `uk_userId` (`userId`),
KEY `fk_userSettings_userId` (`userId`)
) ENGINE=MyISAM AUTO_INCREMENT=6 DEFAULT CHARSET=latin1;
As you discovered, MyISAM doesn't support foreign keys. Both users and userSettings must be InnoDB.
[I'm] just curious if having a UNIQUE_KEY and FOREIGN_KEY in same column is a good practice
This means the userSettings table can have at most one row for each userId. I guess you need only one row per userId because you store an "array" of settings encoded somehow in your settingsArray TEXT column. This is not a good practice.
You should either store each setting in its own column:
CREATE TABLE `userSettings` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`userId` int(11) unsigned NOT NULL,
`isAdmin` bool NOT NULL,
`timezone` varchar(10) NOT NULL,
`theme` varchar(10) NOT NULL,
...other settings...
PRIMARY KEY (`id`),
UNIQUE KEY `uk_userId` (`userId`),
KEY `fk_userSettings_userId` (`userId`)
)
Or else store multiple rows per userId, with one setting name and value per row.
CREATE TABLE `userSettings` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`userId` int(11) unsigned NOT NULL,
`setting` varchar(20) NOT NULL,
`value` varchar(255) NOT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `uk_userId` (`userId`,`setting`),
KEY `fk_userSettings_userId` (`userId`)
)
It's also puzzling why you need an id column for the primary key, if the userId is already NOT NULL and UNIQUE, and that's probably the key you'll use to look up rows anyway. You can make the userId the PRIMARY KEY as well (or userId, setting in the second example), and omit the id column.
Just realized for the table users the ENGINE was InnoDB and for the userSettings table ENGINE was MyISAM, changed that and worked, im just curious if having a UNIQUE_KEY and FOREIGN_KEY in same column is a good practice
I have a forgiven key issue using MySQL. I have a studies table and a samples table. Users can add studies and also add samples. every sample belongs to a study, but studies can have many samples. So theres a one to many relationship with studies and samples. I need to set up a foreign key in the samples table so that whenever a new sample is created it can be referenced by its parent study. I set up a foreign key in the sample table with this script below, but whenever I add a new sample it leaves the study_id column empty. I’m new using foreign keys so any examples would be great. Thanks.
CREATE TABLE `studies` (
`study_id` int(11) NOT NULL AUTO_INCREMENT,
`user_id` int(11) DEFAULT NULL,
`study_name` varchar(45) DEFAULT NULL,
`description` tinytext,
`reads` varchar(45) DEFAULT NULL,
`created_at` varchar(45) DEFAULT NULL,
PRIMARY KEY (`study_id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=latin1;
CREATE TABLE `samples` (
`sample_id` int(11) NOT NULL AUTO_INCREMENT,
`study_id` int(11) DEFAULT NULL,
`sample_name` varchar(45) DEFAULT NULL,
`created_at` varchar(45) DEFAULT NULL,
PRIMARY KEY (`sample_id`),
FOREIGN KEY (`study_id`)
REFERENCES `studies` (`study_id`)
ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=latin1;
Can someone please explain the cause for the following error, 'Can't create table 'Activities' (errno: 150)'
I'm under the understading that the data types and lengths have to be the same, does is have anything to do with the auto increment?
Create Table `LinkMemberActivity` (
`LinkID` int(11) unsigned NOT NULL AUTO_INCREMENT,
`MID` int(11) unsigned NOT NULL,
`AID` int(11) unsigned NOT NULL,
PRIMARY KEY (`LinkID`),
FOREIGN KEY (`MID`) REFERENCES Members(`MID`)) ENGINE=InnoDB DEFAULT CHARSET=latin1;
)
CREATE TABLE `Activities` (
`AID` int(11) unsigned NOT NULL AUTO_INCREMENT,
`Name` varchar(25) DEFAULT NULL,
`MaxCapacity` int(25) DEFAULT NULL,
`StartTime` time DEFAULT NULL,
`EndTime` time DEFAULT NULL,
PRIMARY KEY (`AID`),
FOREIGN KEY (`AID`) REFERENCES LinkMemberActivity(`AID`))
ENGINE=InnoDB DEFAULT CHARSET=latin1 );
You are trying to make a primary key column a foreign key dependent field. This is not only unusual but makes no sense in a datamodel, unless it is part of a composite key. Common practice has a column foreign key dependent on another tables primary key. Not sure what reasons you have for the way you designed your datamodel this way, but you can fix this problem by creating a not null autoincrement column named ID and make this column the primary key. Next remove autoincrement from aid.
Mysql database question. There is system with objects(Domains). Each domain has own table. All objects has unique 16 varchar id - guid
CREATE TABLE `guid` (
`guid` varchar(16) NOT NULL,
`obj_type` varchar(45) NOT NULL,
`obj_id` varchar(45) NOT NULL,
`actived` tinyint(4) NOT NULL DEFAULT '1',
PRIMARY KEY (`guid`)
)
ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE `product` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(150) NOT NULL,
/*....*/
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
CREATE TABLE `catalog` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(150) NOT NULL,
/*....*/
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
I would like connect table guid(fields: obj_type, obj_id) and domain tables(field:id) through foreign key.
Foreign key relationships involve a parent table that holds the central data values, and a child table with identical values pointing back to its parent. The FOREIGN KEY clause is specified in the child table. The parent and child tables must both be InnoDB tables. They must not be TEMPORARY tables.
CREATE TABLE product
(
id INT(11) NOT NULL auto_increment,
name VARCHAR(150) NOT NULL,
PRIMARY KEY (id),
FOREIGN KEY (id) REFERENCES guid (guid )
)
engine=myisam
DEFAULT charset=utf8;