I have a child table that depends on two parent tables that are not related. i want to insert rows into child table

Question

I am creating a database for selling houses.

I have a parent table that I am calling location that has three columns :

• locationLat : the latitude of location of property
• locationLong : the longitude of the property
• locationName : an alternative name that i can use to identify the location of the property by name

Both locationLat and locationlong make up a composite primary key of this table.

Then I have a child table called houseToLet , this table only stores the houses that are for letting. I have similar different tables houseToBuy , fullyFurnished , landtoSell etc. The table for houseTolet has a composite primary key like the location table above ie locationLat , locationLong and a foreign composite key location_locationLat and location_locationLong that references the location table.

Then I have another table called generalFeatures . This the table where I store general features of all the properties I am selling. So generalFeatures table is a child table of houseTolet and Housetobuy as well as Fullyfurnished tables,

When I insert rows into the location table, I find no problem as it is the parent table. When i insert rows into houseTolet table I find no problem since it is a child table and I will have inserted the parent location table already. However when I insert into the generalFeatures table I get into problem since it is a child table of housetoBuy as well as other tables including Fullyfurnished .

Please assist me to know how I can do this.

  CREATE TABLE IF NOT EXISTS `foreign`.`location` (
  `locationLat` DECIMAL(10,8) NOT NULL,
  `locationLong` DECIMAL(11,8) NOT NULL,
  `locationName` VARCHAR(35) NOT NULL,
  PRIMARY KEY (`locationLat`, `locationLong`))
ENGINE = InnoDB

CREATE TABLE IF NOT EXISTS `location`.`housetolet` (
  `locationLat` DECIMAL(10,8) NOT NULL,
  `locationLong` DECIMAL(11,8) NOT NULL,
  `type` ENUM('gatedCommunity', 'standalone', 'apartment') NOT NULL,
  `location_locationLat` DECIMAL(10,8) NOT NULL,
  `location_locationLong` DECIMAL(11,8) NOT NULL,
  PRIMARY KEY (`locationLat`, `locationLong`),
  INDEX `fk_housetolet_location_idx` (`location_locationLat` ASC, `location_locationLong` ASC))


CREATE TABLE IF NOT EXISTS `foreign`.`generalfeatures` (
  `locationLat` DECIMAL(10,8) NOT NULL,
  `locationLong` DECIMAL(11,8) NOT NULL,
  `livingAreaAndSize` INT NOT NULL,
  `bedrooms` TINYINT(4) NOT NULL,
  `bathrooms` TINYINT(4) NOT NULL,
  `masterEnsuite` TINYINT(1) NOT NULL,
  `bedroomsWithBathrooms` TINYINT(4) NOT NULL,
  `kitchenAndSize` TINYINT(4) NOT NULL,
  `parkingAndSlots` TINYINT(4) NOT NULL,
  `swimmingPool` TINYINT(1) NOT NULL,
  `liftsAndNumber` TINYINT(4) NOT NULL,
  `CCTV` TINYINT(1) NOT NULL,
  `sizeOfLand` INT(11) NOT NULL,
  `borehole` TINYINT(1) NOT NULL,
  `housetobuy_locationLat` DECIMAL(10,8) NOT NULL,
  `housetobuy_locationLong` DECIMAL(11,8) NOT NULL,
  `housetolet_locationLat` DECIMAL(10,8) NOT NULL,
  `housetolet_locationLong` DECIMAL(11,8) NOT NULL,
  `fullyfurnished_locationLat` DECIMAL(10,8) NOT NULL,
  `fullyfurnished_locationLong` DECIMAL(11,8) NOT NULL,
  PRIMARY KEY (`locationLat`, `locationLong`),
  INDEX `fk_generalfeatures_housetobuy1_idx` (`housetobuy_locationLat` ASC, `housetobuy_locationLong` ASC),
  INDEX `fk_generalfeatures_housetolet1_idx` (`housetolet_locationLat` ASC, `housetolet_locationLong` ASC),
  INDEX `fk_generalfeatures_fullyfurnished1_idx` (`fullyfurnished_locationLat` ASC, `fullyfurnished_locationLong` ASC),
  CONSTRAINT `fk_generalfeatures_housetobuy1`
    FOREIGN KEY (`housetobuy_locationLat` , `housetobuy_locationLong`)
    REFERENCES `foreign`.`housetobuy` (`locationLat` , `locationLong`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `fk_generalfeatures_housetolet1`
    FOREIGN KEY (`housetolet_locationLat` , `housetolet_locationLong`)
    REFERENCES `foreign`.`housetolet` (`locationLat` , `locationLong`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `fk_generalfeatures_fullyfurnished1`
    FOREIGN KEY (`fullyfurnished_locationLat` , `fullyfurnished_locationLong`)
    REFERENCES `foreign`.`fullyfurnished` (`locationLat` , `locationLong`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)

I want to be able to insert rows into generalFeatures table for houses to Let without getting foreign key constraints that I need to update other tables like houseTobuy or fullyFurnished first, this is because in a particular instance I will be updating a particular type of a house only but not many options. A house to let cannot be at the same time be a house to buy in my case.

Answer 1

Your database design has flaws. Namely, you are storing in multiple tables information that could be represented as a single record. As it is, it looks like all tables could be merged into main table locations :

• the house* tables ( houseToLet , houseToBuy , ...) are just there to store the current status of the location (to let, to buy, ...) : this could be represented as an ENUM field in the location table (or as several boolean columns if more than one status can be enabled at a time)

• the generalFeatures table also seems to contain a single record for each location, hence all of its fields could be moved to the location table.

Using a single table appears like the right design for your use case (and it sure avoids issues with foreign constraints...).

Other considerations : use an autoincremented integer as primary key instead of a composite key (for this, you can create a UNIQUE constraint).

Here is a sample DDL for your table :

CREATE TABLE IF NOT EXISTS `foreign`.`location` (

    -- primary key
    `id` INT AUTO_INCREMENT,
    PRIMARY KEY (`id`),

    -- original columns
    `locationLat` DECIMAL(10,8) NOT NULL,
    `locationLong` DECIMAL(11,8) NOT NULL,
    `locationName` VARCHAR(35) NOT NULL,

    -- house status
    `status` ENUM('toLet', 'houseToBuy', 'fullyFurnished', 'landtoSell') NOT NULL,

    -- columns from `generalfeatures`
    `livingAreaAndSize` INT NOT NULL,
    `bedrooms` TINYINT(4) NOT NULL,
    `bathrooms` TINYINT(4) NOT NULL,
    `masterEnsuite` TINYINT(1) NOT NULL,
    `bedroomsWithBathrooms` TINYINT(4) NOT NULL
    -- other columns from `generalfeatures`...
)ENGINE = INNODB;