What is wrong with my mysql foreign key constraints?

What is wrong with my mysql foreign key constraints?

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What is wrong with my mysql foreign key constraints?
Tag : mysql , By : jonagh
Date : January 12 2021, 08:33 AM

like below fixes the issue You probably just need to fix your constraints in table days to use the composite key from reoccurrences:
  `reoccurrence` varchar(15) NOT NULL,
  `username` varchar(31) NOT NULL DEFAULT '',
  `day` tinyint(2) NOT NULL,
  PRIMARY KEY (`reoccurrence`,`username`,`day`),
  CONSTRAINT `fk_days_reoccurrence` FOREIGN KEY (`reoccurrence`,`username`) REFERENCES `reoccurrences` (`name`,`username`)

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mysql foreign key constraints

Tag : mysql , By : Juice
Date : March 29 2020, 07:55 AM
it fixes the issue Did you specify ON DELETE CASCADE ? when you created your FK? Don't know which engine you are using either
                     PRIMARY KEY (id)
CREATE TABLE child (id INT, parent_id INT,
                    INDEX par_ind (parent_id),
                    FOREIGN KEY (parent_id) REFERENCES parent(id)
                      ON DELETE CASCADE

Why use Foreign Key constraints in MySQL?

Tag : sql , By : Nougat
Date : March 29 2020, 07:55 AM
help you fix your problem Foreign keys enforce referential integrity. These constraints guarantee that a row in a table order_details with a field order_id referencing an orders table will never have an order_id value that doesn't exist in the orders table.
Foreign keys aren't required to have a working relational database (in fact MySQL's default storage engine doesn't support FKs), but they are definitely essential to avoid broken relationships and orphan rows (ie. referential integrity). The ability to enforce referential integrity at the database level is required for the C in ACID to stand.

Foreign Key constraints in MySQL

Tag : php , By : lewing
Date : March 29 2020, 07:55 AM
wish help you to fix your issue I am a newbie to PHP. I have been given the code snippet below as homework: , You can do that like this :
CREATE  TABLE `admin_log`   (
`statusdate`    DATETIME    DEFAULT NULL,
`type` INT(11) DEFAULT  NULL,

 INDEX (type),
    REFERENCES type(id)

PRIMARY KEY (`id`)  

MySQL foreign key constraints through more tables

Tag : mysql , By : Stephen
Date : March 29 2020, 07:55 AM
hope this fix your issue An SQL FK constraint says its referencing column list subrow values, if all non-NULL, have to appear as subrow values for its referenced column list, which must be declared UNIQUE/PK in a base table.
Your constraint is not an SQL FK constraint.
Contract(person_name) REFERENCES
    (SELECT name FROM Person p JOIN Employee e ON p.name = e.name)(name)

How can a relational database with foreign key constraints ingest data that may be in the wrong order?

Tag : postgresql , By : Robin Buitenhuis
Date : March 29 2020, 07:55 AM
fixed the issue. Will look into that further You have a business workflow problem, because line items of individual orders are coming in before the orders themselves have come in. One workaround, perhaps not ideal, would be to create a before insert trigger which checks, for every incoming insert to the line_item table, whether that order already exists in the order table. If not, then it will first insert the order record before trying the insert on line_item.
CREATE OR REPLACE FUNCTION "public"."fn_insert_order" () RETURNS trigger AS $$
    INSERT INTO "order" (order_number)
    SELECT NEW.order_number
    WHERE NOT EXISTS (SELECT 1 FROM "order" WHERE order_number = NEW.order_number);
LANGUAGE 'plpgsql'

# trigger 
CREATE TRIGGER "trigger_insert_order"
EXECUTE PROCEDURE fn_insert_order()
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