How create two columns with same foreign keys - mysql

I am trying to create two column with same foreign key . This is Error in Mysql.
ERROR
errno: 150 “Foreign key constraint is incorrectly formed”
SCRIPT
CREATE TABLE IF NOT EXISTS `invictus`.`Votaciones` (
`idVotaciones` INT NOT NULL AUTO_INCREMENT,
`mvp` INT NOT NULL,
`idPartido-Jugador` INT NOT NULL,
`votante` INT NOT NULL,
PRIMARY KEY (`idVotaciones`),
INDEX `fk_Votaciones_Partido-Jugadores_idx` (`mvp` ASC, `idPartido-Jugador` ASC, `votante` ASC),
CONSTRAINT `fk_Votaciones_Partido-Jugadores`
FOREIGN KEY (`mvp` , `idPartido-Jugador` , `votante`)
REFERENCES `invictus`.`Partido-Jugadores` (`Jugador_idJugador` , `Equipos_Partido_idPartido` , `Jugador_idJugador`)
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB;
EDIT 1
Here the table Partido-Jugadores , where I want to reference my two colums with Jugador_idJugador
CREATE TABLE IF NOT EXISTS `invictus`.`Partido-Jugadores` (
`idPartido-Jugadores` INT NOT NULL AUTO_INCREMENT,
`Equipos_idEquipos` INT NOT NULL,
`Equipos_Partido_idPartido` INT NOT NULL,
`Equipos_Partido_fecha` DATETIME NOT NULL,
`Equipos_Partido_Grupo_idGrupo` INT NOT NULL,
`Equipos_nombreEquipo` VARCHAR(45) NOT NULL,
`Jugador_idJugador` INT NOT NULL,
PRIMARY KEY (`idPartido-Jugadores`, `Equipos_idEquipos`, `Equipos_Partido_idPartido`, `Equipos_Partido_fecha`, `Equipos_Partido_Grupo_idGrupo`, `Equipos_nombreEquipo`, `Jugador_idJugador`),
INDEX `fk_Partido-Jugadores_Equipos1_idx` (`Equipos_idEquipos` ASC, `Equipos_Partido_idPartido` ASC, `Equipos_Partido_fecha` ASC, `Equipos_Partido_Grupo_idGrupo` ASC, `Equipos_nombreEquipo` ASC),
INDEX `fk_Partido-Jugadores_Jugador1_idx` (`Jugador_idJugador` ASC),
CONSTRAINT `fk_Partido-Jugadores_Equipos1`
FOREIGN KEY (`Equipos_idEquipos` , `Equipos_Partido_idPartido` , `Equipos_Partido_fecha` , `Equipos_Partido_Grupo_idGrupo` , `Equipos_nombreEquipo`)
REFERENCES `invictus`.`Equipos` (`idEquipos` , `Partido_idPartido` , `Partido_fecha` , `Partido_Grupo_idGrupo` , `nombreEquipo`)
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `fk_Partido-Jugadores_Jugador1`
FOREIGN KEY (`Jugador_idJugador`)
REFERENCES `invictus`.`Miembros-Grupo` (`Jugador_idJugador`)
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB;
What is the problem?
Thanks !

If you want the correct syntax, you will need to show what the primary key for Partido-Jugadores looks like.
However, you have repeated a column twice in the foreign key reference:
REFERENCES `invictus`.`Partido-Jugadores` (**`Jugador_idJugador`**, `Equipos_Partido_idPartido` , **`Jugador_idJugador`**)
I've never tried this, but I assume that it is an error in the definition of the primary key, and an error in the foreign key reference. Use the appropriate primary key definition.
EDIT:
If you have an auto-increment column in Partido-Jugadores, then that should be the primary key. That alone with nothing else:
PRIMARY KEY (`idPartido-Jugadores`),
Then the foreign key reference would be:
CONSTRAINT `fk_Votaciones_Partido-Jugadores`
FOREIGN KEY (`idPartido-Jugador)
REFERENCES `invictus`.`Partido-Jugadores` (`Jugador_idJugadores`)
ON DELETE NO ACTION ON UPDATE NO ACTION
Notes:
You should name the primary key in the singular, in my opinion.
You should not use - in table or column names. Use _ as a separator instead. That way, identifiers do not need to be escaped.

Related

MySQL 8 NULL foreign key

I am creating some new tables and i want tot populate them with data for tests and i got into this problem with mysql 8.
I always worked with null FK on tables but now i don't know what is happening.
I think is something from mysql 8, i updated recently and i didn't have problems with it till now.
I am using 8.0.12.
error that i get is :
[23000][1452] Cannot add or update a child row: a foreign key
constraint fails (i2cwac_test.site_board_pins, CONSTRAINT
site_board_pins_sensor_types_id_fk FOREIGN KEY (id) REFERENCES
sensor_types (id))
table creation script:
CREATE TABLE site_board_pins
(
id bigint(20) PRIMARY KEY NOT NULL AUTO_INCREMENT,
site_board_id bigint(20) NOT NULL,
e_board_pin_id bigint(20) NOT NULL,
pin_type_id bigint(20) NOT NULL,
pin_operation_mode bigint(20) NULL,
sensor_type_id bigint(20) NULL,
enabled bit(1) NOT NULL ,
description varchar(500),
CONSTRAINT site_board_pins_site_boards_id_fk FOREIGN KEY (id) REFERENCES site_boards (id),
CONSTRAINT site_board_pins_e_board_pins_id_fk FOREIGN KEY (id) REFERENCES e_board_pins (id),
CONSTRAINT site_board_pins_pin_types_id_fk FOREIGN KEY (id) REFERENCES pin_types (id),
CONSTRAINT site_board_pins_pin_operation_mode_id_fk FOREIGN KEY (id) REFERENCES pin_operation_mode (id),
CONSTRAINT site_board_pins_sensor_types_id_fk FOREIGN KEY (id) REFERENCES sensor_types (id)
);
insert that fails :
INSERT INTO `site_board_pins` (`site_board_id`, `e_board_pin_id`, `pin_type_id`, `pin_operation_mode`, `sensor_type_id`, `enabled`)
VALUES
((select id from e_boards where name = 'Iboard Pro 1.1'),
(select ep.id from e_boards eb join e_board_pins ep on ep.e_board_id = eb.id where eb.name = 'Iboard Pro 1.1' and ep.name = 'A1'),
(select id from pin_types where mode = 'Analog'),
NULL,
NULL,
0);
Thanks in advance
Looks like you've messed up your FK definitions - all the FKs are declared say that your Id column exists in all these other tables.
For example, I'm pretty sure your first one is meant to be:
CONSTRAINT site_board_pins_site_boards_id_fk FOREIGN KEY (site_board_id) REFERENCES site_boards (id)

mysql error 150 from referencing same foreign key column in two tables

I have looked through quite a few posts but havent found the solution for my problem. My suspicion is the error stems from me trying to use a single column to reference the same primary key column in two different tables. Specifically the bid table has the foreign key simulation_id that is also present in the bidder and item_round_status tables. the bid table references the foreign keys of both of these tables but I would like to use only one simulation_id column in the table. Is this the source of the Error 150 problem?
-- -----------------------------------------------------
-- Table `kffg_simulations`.`item_round_status`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `kffg_simulations`.`item_round_status` (
`simulation_id` INT NOT NULL ,
`round` INT NOT NULL ,
`clock_item_id` INT NOT NULL ,
`posted_price` BIGINT NOT NULL ,
`clock_price` BIGINT NOT NULL ,
PRIMARY KEY (`simulation_id`, `round`, `clock_item_id`) ,
INDEX `fk_item_round_status_clock_item1_idx` (`clock_item_id` ASC) ,
INDEX `fk_item_round_status_simulation1_idx` (`simulation_id` ASC) ,
CONSTRAINT `fk_item_round_status_clock_item1`
FOREIGN KEY (`clock_item_id`)
REFERENCES `kffg_simulations`.`clock_item` (`id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `fk_item_round_status_simulation1`
FOREIGN KEY (`simulation_id`)
REFERENCES `kffg_simulations`.`simulation` (`id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB;
-- -----------------------------------------------------
-- Table `kffg_simulations`.`bidder`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `kffg_simulations`.`bidder` (
`simulation_id` INT NOT NULL ,
`idx` INT NOT NULL ,
`bidder_strategy_id` INT NOT NULL ,
`budget` BIGINT NOT NULL ,
PRIMARY KEY (`simulation_id`, `idx`) ,
INDEX `fk_bidder_simulation1_idx` (`simulation_id` ASC) ,
INDEX `fk_bidder_bidder_strategy1_idx` (`bidder_strategy_id` ASC) ,
CONSTRAINT `fk_bidder_simulation1`
FOREIGN KEY (`simulation_id`)
REFERENCES `kffg_simulations`.`simulation` (`id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `fk_bidder_bidder_strategy1`
FOREIGN KEY (`bidder_strategy_id`)
REFERENCES `kffg_simulations`.`bidder_strategy` (`id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB;
-- -----------------------------------------------------
-- Table `kffg_simulations`.`bid_type`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `kffg_simulations`.`bid_type` (
`id` INT NOT NULL AUTO_INCREMENT ,
`name` VARCHAR(45) NOT NULL ,
PRIMARY KEY (`id`) )
ENGINE = InnoDB;
-- -----------------------------------------------------
-- Table `kffg_simulations`.`bid_status`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `kffg_simulations`.`bid_status` (
`id` INT NOT NULL AUTO_INCREMENT ,
`description` VARCHAR(45) NOT NULL ,
PRIMARY KEY (`id`) )
ENGINE = InnoDB;
-- -----------------------------------------------------
-- Table `kffg_simulations`.`bid`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `kffg_simulations`.`bid` (
`simulation_id` INT NOT NULL ,
`item_round_status_round` INT NOT NULL ,
`clock_item_id` INT NOT NULL ,
`bidder_idx` INT NOT NULL ,
`quantity` INT NOT NULL ,
`price` INT NOT NULL ,
`bid_type_id` INT NOT NULL ,
`switch_to_pea_category_id` INT NOT NULL ,
`backstop` BIGINT NULL ,
`bid_status_id` INT NOT NULL ,
`processed_demand` INT NOT NULL ,
PRIMARY KEY (`simulation_id`, `item_round_status_round`, `clock_item_id`, `bidder_idx`, `quantity`) ,
INDEX `fk_bid_item_round_status1_idx` (`simulation_id` ASC, `item_round_status_round` ASC, `clock_item_id` ASC) ,
INDEX `fk_bid_bidder1_idx` (`simulation_id` ASC, `bidder_idx` ASC) ,
INDEX `fk_bid_bid_type1_idx` (`bid_type_id` ASC) ,
INDEX `fk_bid_pea_category1_idx` (`switch_to_pea_category_id` ASC) ,
INDEX `fk_bid_bid_status1_idx` (`bid_status_id` ASC) ,
CONSTRAINT `fk_bid_item_round_status1`
FOREIGN KEY (`simulation_id` , `item_round_status_round` , `clock_item_id`)
REFERENCES `kffg_simulations`.`item_round_status` (`simulation_id` , `round` , `clock_item_id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `fk_bid_bidder1`
FOREIGN KEY (`bidder_idx` , `simulation_id`)
REFERENCES `kffg_simulations`.`bidder` (`idx` , `simulation_id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `fk_bid_bid_type1`
FOREIGN KEY (`bid_type_id`)
REFERENCES `kffg_simulations`.`bid_type` (`id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `fk_bid_pea_category1`
FOREIGN KEY (`switch_to_pea_category_id`)
REFERENCES `kffg_simulations`.`pea_category` (`id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `fk_bid_bid_status1`
FOREIGN KEY (`bid_status_id`)
REFERENCES `kffg_simulations`.`bid_status` (`id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB;
Updated to show error message:
------------------------
LATEST FOREIGN KEY ERROR
------------------------
170604 21:52:27 Error in foreign key constraint of table kffg_simulations/bid:
FOREIGN KEY (`simulation_id` , `item_round_status_round` , `clock_item_id`)
REFERENCES `kffg_simulations`.`item_round_status` (`simulation_id` , `round` , `clock_item_id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `fk_bid_bidder1`
FOREIGN KEY (`bidder_idx` , `simulation_id`)
REFERENCES `kffg_simulations`.`bidder` (`idx` , `simulation_id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `fk_bid_bid_type1`
FOREIGN KEY (`bid_type_id`)
REFERENCES `kffg_simulations`.`bid_type` (`id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `fk_bid_pea_category1`
FOREIGN KEY (`switch_to_pea_category_id`)
REFERENCES `kffg_simulations`.`pea_category` (`id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `fk_bid_bid_status1`
FOREIGN KEY (`bid_status_id`)
REFERENCES `kffg_simulations`.`bid_status` (`id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB:
Cannot find an index in the referenced table where the
referenced columns appear as the first columns, or column types
in the table and the referenced table do not match for constraint.
Note that the internal storage type of ENUM and SET changed in
tables created with >= InnoDB-4.1.12, and such columns in old tables
cannot be referenced by such columns in new tables.
See http://dev.mysql.com/doc/refman/5.1/en/innodb-foreign-key-constraints.html
for correct foreign key definition.
Also updated with uml diagram:
Foreign Key Usage and Error Information gives info on FKs (foreign keys).
you can obtain a detailed explanation of the most recent InnoDB foreign key error by checking the output of SHOW ENGINE INNODB STATUS.
InnoDB permits a foreign key to reference any index column or group of columns. However, in the referenced table, there must be an index where the referenced columns are listed as the first columns in the same order.
In bid:
FOREIGN KEY (`bidder_idx` , `simulation_id`)
REFERENCES `kffg_simulations`.`bidder` (`idx` , `simulation_id`)
The "referenced table" here is bidder, the "referenced columns" list is (idx , simulation_id).
Cannot find an index in the referenced table where the
referenced columns appear as the first columns,
Sure enough, in bidder the closest we find is:
PRIMARY KEY (`simulation_id`, `idx`) ,
which implicitly declares a default unique not null index, but like all the other indexes doesn't start with the FK's column list.
Philipxy thank you for your help on this problem. You were correct in the comment that the foreign key for bidder was wrong. For some reason mysql workbench generated the columns in the code in the wrong order. The code provided by mysqlworkbench is below:
CONSTRAINT `fk_bid_bidder1`
FOREIGN KEY (`bidder_idx` , `simulation_id`)
REFERENCES `kffg_simulations`.`bidder` (`idx` , `simulation_id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION,
And the following code works properly:
CONSTRAINT `fk_assignment_bidder1`
FOREIGN KEY (`bidder_simulation_id` , `bidder_idx`)
REFERENCES `kffg_simulations`.`bidder` (`simulation_id` , `idx`)
ON DELETE NO ACTION
ON UPDATE NO ACTION,
As far as I can tell I had the indexing setup properly but the code was generate in the wrong order.
(I used mysql workbench forward engineer to generate the sql script. I used the gui to create the relationships between the bid table, bidder, and item_round_status. Since both of those tables have simulationid as pk it duplicated that column. When I manually adjusted the foreign key for bidder to reference the simulationid column generated for item_round_status it changed the indices related to that foreign key. I manually changed them to the proper indices but it seems to ignore my changes when generating the script causing the error.)

Mysql composite key out of a foreign composite key

I'm trying to make a many-to-many relationship between two tables In Mysql WorkBench, and one of those 2 tables has a composite primary key ( parts are coming from 2 foreign keys). When I'm trying to generate the SQL I'm getting this error :
ERROR: Error 1215: Cannot add foreign key constraint
SQL Code:
-- -----------------------------------------------------
-- Table `A_D_schema`.`Resources_has_OwnerGroups`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `A_D_schema`.`Resources_has_OwnerGroups` (
`Resources_id` INT NOT NULL,
`OwnerGroups_id` INT NOT NULL,
`OwnerGroups_Instances_has_Customers_Instances_idInstances` INT NOT NULL,
`OwnerGroups_Instances_has_Customers_Customers_idCustomers` INT NOT NULL,
PRIMARY KEY (`Resources_id`, `OwnerGroups_id`, `OwnerGroups_Instances_has_Customers_Instances_idInstances`, `OwnerGroups_Instances_has_Customers_Customers_idCustomers`),
INDEX `fk_Resources_has_OwnerGroups_OwnerGroups1_idx` (`OwnerGroups_id` ASC, `OwnerGroups_Instances_has_Customers_Instances_idInstances` ASC, `OwnerGroups_Instances_has_Customers_Customers_idCustomers` ASC),
INDEX `fk_Resources_has_OwnerGroups_Resources1_idx` (`Resources_id` ASC),
CONSTRAINT `fk_Resources_has_OwnerGroups_Resources1`
FOREIGN KEY (`Resources_id`)
REFERENCES `A_D_schema`.`Resources` (`id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `fk_Resources_has_OwnerGroups_OwnerGroups1`
FOREIGN KEY (`OwnerGroups_id` , `OwnerGroups_Instances_has_Customers_Instances_idInstances` , `OwnerGroups_Instances_has_Customers_Customers_idCustomers`)
REFERENCES `A_D_schema`.`OwnerGroups` (`id` , `Instances_has_Customers_Instances_idInstances` , `Instances_has_Customers_Customers_idCustomers`)
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB
From the SHOW ENGINE INNODB STATUS I can see this message :
Cannot resolve column name close to:
)
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `fk_Resources_has_OwnerGroups_OwnerGroups1`
FOREIGN KEY (`OwnerGroups_id` , `OwnerGroups_Instances_has_Customers_Instances_idInstances` , `OwnerGroups_Instances_has_Customers_Customers_idCustomers`)
REFERENCES `A_D_schema`.`OwnerGroups` (`id` , `Instances_has_Customers_Instances_idInstances` , `Instances_has_Customers_Customers_idCustomers`)
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB
The SHOW CREATE TABLE Resources and SHOW CREATE TABLE OwnerGroups :
CREATE TABLE `Resources` (
`idResources` int(11) NOT NULL AUTO_INCREMENT,
`email` varchar(45) DEFAULT NULL,
`role` int(11) DEFAULT NULL COMMENT 'role : 1 disptcher \n0 admin',
PRIMARY KEY (`idResources`),
UNIQUE KEY `idresources_UNIQUE` (`idResources`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
CREATE TABLE `OwnerGroups` (
`idOwnerGroups` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(45) DEFAULT NULL,
`group` int(11) DEFAULT NULL,
PRIMARY KEY (`idOwnerGroups`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
CONSTRAINT `fk_Resources_has_OwnerGroups_Resources1`
FOREIGN KEY (`Resources_id`)
REFERENCES `A_D_schema`.`Resources` (`id`)
Your Resources table doesn't have a column id. Its primary key is idResources.
CONSTRAINT `fk_Resources_has_OwnerGroups_OwnerGroups1`
FOREIGN KEY (`OwnerGroups_id` , `OwnerGroups_Instances_has_Customers_Instances_idInstances` , `OwnerGroups_Instances_has_Customers_Customers_idCustomers`)
REFERENCES `A_D_schema`.`OwnerGroups` (`id` , `Instances_has_Customers_Instances_idInstances` , `Instances_has_Customers_Customers_idCustomers`)
Your OwnerGroups table doesn't have a column id. Its primary key is idOwnerGroups. It doesn't have the other two columns you reference at all.
In general, when you declare a foreign key, first you name the columns in the child table:
CREATE TABLE Child (
childCol1 INT,
childCol2 INT,
...
FOREIGN KEY (childCol1, childCol2) ...
Then you reference columns in the parent table:
... REFERENCES Parent (parentCol1, parentCol2)
);
You must use the names of columns as they exist in the parent table.
The columns you reference in the parent table must together be the PRIMARY KEY or UNIQUE KEY of that table. In other words, given the example above, it would not work against this Parent table:
CREATE TABLE Parent (
parentCol1 INT,
parentCol2 INT,
PRIMARY KEY (parentCol1)
);
Because the PRIMARY KEY does not include parentCol2.
In your case, the following should work:
CREATE TABLE IF NOT EXISTS `A_D_schema`.`Resources_has_OwnerGroups` (
`Resources_id` INT NOT NULL,
`OwnerGroups_id` INT NOT NULL,
`OwnerGroups_Instances_has_Customers_Instances_idInstances` INT NOT NULL,
`OwnerGroups_Instances_has_Customers_Customers_idCustomers` INT NOT NULL,
PRIMARY KEY (`Resources_id`, `OwnerGroups_id`, `OwnerGroups_Instances_has_Customers_Instances_idInstances`, `OwnerGroups_Instances_has_Customers_Customers_idCustomers`),
CONSTRAINT `fk_Resources_has_OwnerGroups_Resources1`
FOREIGN KEY (`Resources_id`)
REFERENCES `A_D_schema`.`Resources` (`idResources`)
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `fk_Resources_has_OwnerGroups_OwnerGroups1`
FOREIGN KEY (`OwnerGroups_id`)
REFERENCES `A_D_schema`.`OwnerGroups` (`idOwnerGroups`)
ON DELETE NO ACTION
ON UPDATE NO ACTION
) ENGINE = InnoDB
I took out a couple of INDEX definitions that are redundant. You don't need to index your PRIMARY KEY, it's already the clustered index of the table. You don't need to index the column you use in a foreign key declaration, MySQL will index that column automatically if it need to (though if an index already exists for that column, the FK constraint will use that index).
I'm not sure I understand what your other two columns OwnerGroups_Instances_has_Customers_Instances_idInstances and OwnerGroups_Instances_has_Customers_Customers_idCustomers are meant to do. Typically in a many-to-many table, you only need enough columns to reference the primary keys of the respective parent tables.
Re your comment:
You should try refreshing the view of the schema from time to time. There's a button with a pair of curvy arrows, to the right of "SCHEMAS".

Foreign key on different tables

I have a images table:
Images
image_id
image_type ('foo', 'bar')
type_id
How can I create a foreign key so if the image_type is foo, type_id should relate to foo table, if image_type is bar to bar table.
What you're trying to do is to create a supertype. In SQL this is best modeled like below (IMO at least). My apologies if the syntax isn't quite right for MySQL. I usually use MS SQL Server.
CREATE TABLE Image_Types (
image_type_id INT NOT NULL,
image_type CHAR(3) NOT NULL CONSTRAINT CHK_Image_Types_image_type CHECK (image_type IN ('Foo', 'Bar')),
CONSTRAINT PK_Image_Types PRIMARY KEY (image_type_id, image_type)
)
CREATE TABLE Foo (
image_type_id INT NOT NULL,
image_type CHAR(3) NOT NULL CONSTRAINT CHK_Foo_image_type CHECK (image_type IN ('Foo')),
some_foo_specific_column VARCHAR(100) NOT NULL,
CONSTRAINT PK_Foo PRIMARY KEY (image_type_id),
CONSTRAINT FK_Foo_ImageTypes FOREIGN KEY (image_type_id, image_type) REFERENCES Image_Types (image_type_id, image_type)
)
CREATE TABLE Bar (
image_type_id INT NOT NULL,
image_type CHAR(3) NOT NULL CONSTRAINT CHK_Bar_image_type CHECK (image_type IN ('Bar')),
some_bar_specific_column VARCHAR(100) NOT NULL,
CONSTRAINT PK_Bar PRIMARY KEY (image_type_id),
CONSTRAINT FK_Bar_ImageTypes FOREIGN KEY (image_type_id, image_type) REFERENCES Image_Types (image_type_id, image_type)
)
CREATE TABLE Images (
image_id INT NOT NULL,
image_type CHAR(3) NOT NULL CONSTRAINT CHK_Images_image_type CHECK (image_type IN ('Foo', 'Bar')),
image_type_id INT NOT NULL,
CONSTRAINT PK_Images PRIMARY KEY (image_id),
CONSTRAINT FK_Images_ImageTypes FOREIGN KEY (image_type_id, image_type) REFERENCES Image_Types (image_type_id, image_type)
)
An alternative approach, if your RDBMS supports it, is to use filtered indexed views on Image_Types and then have your FKs in Foo and Bar point at those views. That allows you to eliminate the image_type column from some of your tables. Some people prefer the above pattern even when filtered indexed views are available though.

SQL : ERROR 1005: Can't create table 'obl2.itemsubjects' (errno: 121)

I have the following tables:
CREATE TABLE `OBL2`.`item` (
`itemID` INT NOT NULL AUTO_INCREMENT ,
`itemName` VARCHAR(45) NOT NULL ,
PRIMARY KEY (`itemID`) ,
INDEX `itemName` (`itemName` ASC) );
CREATE TABLE `OBL2`.`subject` (
`subjectID` INT NOT NULL ,
`subjectName` VARCHAR(45) NOT NULL ,
PRIMARY KEY (`subjectID`) );
Now since the connection is many to many, each item can have many subject and each subject can be related to many items - I'd like to set a connection table.
This is my code:
CREATE TABLE `OBL2`.`itemsubjects` (
`itemID` INT NOT NULL ,
`subjectID` INT NOT NULL ,
PRIMARY KEY (`itemID`, `subjectID`) ,
INDEX `itemID_idx` (`itemID` ASC) ,
INDEX `subjectID_idx` (`subjectID` ASC) ,
CONSTRAINT `itemID`
FOREIGN KEY (`itemID` )
REFERENCES `OBL2`.`item` (`itemID` )
ON DELETE CASCADE
ON UPDATE CASCADE,
CONSTRAINT `subjectID`
FOREIGN KEY (`subjectID` )
REFERENCES `OBL2`.`subject` (`subjectID` )
ON DELETE CASCADE
ON UPDATE CASCADE);
but for some reason the code of the 3rd table is not being accepted.
I get an error message:
ERROR 1005: Can't create table 'obl2.itemsubjects' (errno: 121)
I've read about the error on the internet and it says it's a known issue of MYSQL yet there are no solutions.
Any thoughts?
The MySQL docs say in FOREIGN KEY Constraints (emphasis mine):
If the CONSTRAINT symbol clause is given, the symbol value must be unique in the database. If the clause is not given, InnoDB creates the name automatically.
So, the reason that the itemsubject table creation failed, was that you had another (foreign key) constraint, named itemID, or one named subjectID in some other table of the database.
It's good to have a naming conevntion that is standard across the database. Just as you have ColumnName_idx for indices, you can use ReferencedTable_ReferencingTable_FK for foreign key constraints:
CREATE TABLE OBL2.itemsubjects (
itemID INT NOT NULL ,
subjectID INT NOT NULL ,
PRIMARY KEY
(itemID, subjectID) ,
INDEX itemID_idx -- I like these
(itemID ASC) ,
INDEX subjectID_idx -- two
(subjectID ASC) ,
CONSTRAINT item_itemsubject_FK -- what I propose, here
FOREIGN KEY (itemID)
REFERENCES OBL2.item (itemID)
ON DELETE CASCADE
ON UPDATE CASCADE,
CONSTRAINT subject_itemsubject_FK -- and here
FOREIGN KEY (subjectID)
REFERENCES OBL2.subject (subjectID)
ON DELETE CASCADE
ON UPDATE CASCADE
);