Many people had this problem already, but there was no fitting solution in other posts.
I have two tables, one named "sales", the other named "host_flags". I would like to have a foreign key for host_flags.sales_id to sales.id, but mysql won't let me! I have primary indexes defined in each table, so I wonder why...
The host_flags table already has a foreign key on the column host_id, but even when I tried and created the foreign key for the sales id first, it wouldn't let me.
The tables look like:
CREATE TABLE `sales` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`email` varchar(255) DEFAULT NULL,
`password` varchar(255) DEFAULT NULL,
`creation` datetime DEFAULT NULL,
`lastupdate` timestamp NULL DEFAULT NULL ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=latin1;
CREATE TABLE `host_flags` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`host_id` int(11) DEFAULT NULL,
`sales_id` int(11) DEFAULT NULL,
`creation` datetime DEFAULT NULL,
`lastupdate` timestamp NULL DEFAULT NULL ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (`id`),
KEY `host_id6` (`host_id`),
CONSTRAINT `host_id6` FOREIGN KEY (`host_id`) REFERENCES `hosts` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
CREATE TABLE `hosts` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`creation` datetime NOT NULL,
`lastupdate` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=32225 DEFAULT CHARSET=utf8 COLLATE=utf8_bin;
I get this error message:
MySQL said: Can't create table 'primarydata.#sql-191_1' (errno: 150)
Thanks!
Charles
SOLUTION FOUND
All ints of the primary indexes have to be either signed or unsigned - not mixed.
Typically:
I like to declare the FK constraints outside of the table definition after all tables have been constructed.
ALTER TABLE `tbl`
ADD CONSTRAINT `constr`
FOREIGN KEY `fk_id` REFERENCES `ftbl`(`id`)
ON UPDATE CASCADE
ON DELETE CASCADE;
This way I can make sure the problem isn't something like the datatype of tbl.fk_id not being the same as the one of ftbl.id (including UNSIGNED as #Devart said). Or not having declared ftbl.id as unique. Regardless of the order of declaration of the tables.
After i do this i can integrate the constraint back into the table definition and take into account the order in which the tables need to be created to allow the constraint to be added.
You problem:
-- creating the sales table
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
-- creating the host_flags table
`sales_id` int(11) DEFAULT NULL,
-- the sales.id is declared as unsigned
-- the host_flags.sales_id is declared signed
Additonally to Recursed's answer:
There is a requirement that foreign keys contstraints' names must be unique in database scope. Maybe changing the name will work?
There is also a huge thread on MySQL community forums about the problem containing several solutions for some specific situations.
Possible two errors:
Reference and referenced columns must have the same type - int(11) unsigned
Unknown referenced table hosts.
Related
I have two tables, books and borrowing requests - I am making a study project to learn MySQL. Trying to link these two tables using a FK, and constantly get an error:
"SQLSTATE[HY000]: General error: 1215 Cannot add foreign key constraint")
Apart from documentation, I searched virtually all of the related topics here on SO, however, no success. Types are the same, columns both unsigned, one primary key, etc. - to my understanding I have respected all of the provisions. But it does not work! What am I missing?
Here are the two tables and the fk addition query:
CREATE TABLE `books` (
`book_id` INT(11) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
`book_title` VARCHAR(100) NOT NULL,
`author_id` INT(11) NOT NULL,
`book_condition` INT(5) NOT NULL
) ENGINE=InnoDB AUTO_INCREMENT=23453 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci
CREATE TABLE `borrowing_requests` (
`request_id` INT(11) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
`user_id` INT(11) NOT NULL,
`book_id` INT(11) UNSIGNED NOT NULL,
`due_date` VARCHAR(55) NOT NULL
) ENGINE=InnoDB AUTO_INCREMENT=23453 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;
FK Query:
ALTER TABLE `books` ADD CONSTRAINT books_fk FOREIGN KEY (`book_id`)
REFERENCES `borrowing_requests`(`book_id`)
ON DELETE NO ACTION ON UPDATE NO ACTION
You have the foreign key "backwards" - the borrowing request should reference a book, not the other way round:
ALTER TABLE `borrowing_requests` ADD CONSTRAINT books_fk FOREIGN KEY (`book_id`)
REFERENCES `books`(`book_id`)
ON DELETE NO ACTION ON UPDATE NO ACTION
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.
CREATE TABLE tasks (
`user_id` INT(10) UNSIGNED NOT NULL,
`name` VARCHAR(255) NOT NULL,
`code` VARCHAR(255) NOT NULL,
`params` JSON,
`hash` VARCHAR(32) GENERATED ALWAYS AS (MD5(`params`)),
`created_at` TIMESTAMP NULL DEFAULT NULL,
`updated_at` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (`id`),
CONSTRAINT `tasks_user_id_users_id_fk`
FOREIGN KEY (`user_id`) REFERENCES `users`(`id`)
)ENGINE=INNODB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;
then i try to add a unique index on user_id and hash, i tried to do it during the table create, but there were a problem with the foreign key, so i decided to do it separately.
ALTER TABLE tasks
ADD UNIQUE INDEX `tasks_user_id_hash_unique_idx` (`user_id`, `hash`);
Then i get strange problem error 1146
Table '<dbname>.tasks' doesn't exist
Since then strange errors
1. I cannot delete it while it exists and i cannot do with it anything, cause it does not exist. After mysql reload I get the table deleted but if i try to create it again:
Error Code: 1813
Tablespace '<dbname>.tasks' exists.
I found the decision for unique field, i simply genereate md5( hash + user_id) UNIQUE. But How can I get rid of that problem which still exists and what is going on. It looks like a BUG in mysql Percona 5.7.14-7
so the right way to create the table
CREATE TABLE tasks (
`user_id` INT(10) UNSIGNED NOT NULL,
`name` VARCHAR(255) NOT NULL,
`code` VARCHAR(255) NOT NULL,
`params` JSON,
`hash` VARCHAR(32) GENERATED ALWAYS AS (MD5(CONCAT(`params`,`user_id`))) UNIQUE,
`created_at` TIMESTAMP NULL DEFAULT NULL,
`updated_at` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (`id`),
CONSTRAINT `tasks_user_id_users_id_fk`
FOREIGN KEY (`user_id`) REFERENCES `users`(`id`)
)ENGINE=INNODB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;
But, again, the question with the ghosts still exists after the first tries!
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.
I am sure I am missing something simple.
RequestLog table:
CREATE TABLE `requestlog` (
`RequestID` int(10) unsigned NOT NULL AUTO_INCREMENT,
`RequestName` varchar(30) NOT NULL,
`RequestData` varchar(150) NOT NULL,
`RequestDate` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP,
`Version` varchar(15) NOT NULL,
PRIMARY KEY (`RequestID`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1
ResponseLog table:
CREATE TABLE `responselog` (
`ResponseID` int(10) unsigned NOT NULL AUTO_INCREMENT,
`FK_RequestID` int(10) NOT NULL,
`ResponseText` text NOT NULL,
PRIMARY KEY (`ResponseID`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1
Trying to add a foreign key on ResponseLog.FK_RequestID with
ALTER TABLE ResponseLog
ADD FOREIGN KEY (FK_RequestID) REFERENCES RequestLog(RequestID)
Don't shoot me, what am I missing?
ALTER TABLE references tables ResponseLog and RequestLog. Your CREATE TABLE statements create tables named requestlog and responselog. Try changing your ALTER TABLE statement so that it uses table identifiers with the same case.
Also, and it is probably the main problem, the referenced fields have different data types. One is an int, the other an unsigned int. Data types have to match, otherwise the fields could become inconsistent. MySQL knows this and prevents you from creating a broken foreign key.