Answers for "how to implement foreign key in mysql"

SQL
25

mysql add foreign key

-- On Create
CREATE TABLE tableName (
    ID INT,
    SomeEntityID INT,
    PRIMARY KEY (ID),
    FOREIGN KEY (SomeEntityID)
        REFERENCES SomeEntityTable(ID)
        ON DELETE CASCADE
);

-- On Alter, if the column already exists but has no FK
ALTER TABLE
  tableName
ADD
  FOREIGN KEY (SomeEntityID) REFERENCES SomeEntityTable(ID) ON DELETE CASCADE;
  
 -- Add FK with a specific name
 -- On Alter, if the column already exists but has no FK
ALTER TABLE
  tableName
ADD CONSTRAINT fk_name
  FOREIGN KEY (SomeEntityID) REFERENCES SomeEntityTable(ID) ON DELETE CASCADE;
Posted by: Guest on April-27-2020
0

foreign key type uniqu mysql

mysql > create unique index index_bar_id on foos(bar_id);
mysql > alter table foos add constraint index_bar_id foreign key (bar_id) references bars (id);
Posted by: Guest on October-16-2020

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