PRIMARY KEY (`id`) ); CREATE TABLE `knows` ( `user_id_1` double NOT NULL, `user_id_2` double NOT NULL, KEY `benutzer_id_1` (`benutzer_id_1`), KEY `benutzer_id_2` (`benutzer_id_2`) ); Now ... after creating (using the ALTER command of MySQL) two foreign ...
Once a foreign key has been created, you may find that you wish to drop the foreign key from the table. Let's explore how to do this. TIP: You can not drop a foreign key using ALTER TABLE because SQLite does not support DROP CONSTRAINT in the ALTER TABLE statement. However, we will...
Primary key using the ALTER TABLE command For creating a foreign key on an existing table using the ALTER TABLE command, ALTER TABLE books ADD FOREIGN KEY (author_id) REFERENCES authors(author_id); Let’s DESC the books table: DESC books; We can see that the author_id is set as the ...
Foreign Key With Alter Table It is possible to add theFOREIGN KEYconstraint to an existing table using theALTER TABLEcommand. For example, CREATETABLECustomers (idINT, first_nameVARCHAR(40), last_nameVARCHAR(40), ageINT, countryVARCHAR(10),CONSTRAINTCustomersPK PRIMARYKEY(id) );CREATETABLEOrders...
ADD FOREIGN KEY (CustomerNo) REFERENCES CUSTOMERS (CustomerNo); Any constraint defined using the aboveALTER TABLEcommand can be dropped using theDROP CONSTRAINTcommand. To drop or remove a foreign key, use the following SQL syntax: ALTER TABLE ORDERS ...
ALTERTABLEstudent ADDFOREIGNKEY(city_id)REFERENCEScity(id); Discussion It is also possible to add a new foreign key to an existing table. Here, the table is altered using anALTER TABLEclause. The table name (in our example,student) is placed after theALTER TABLEkeyword. Next, theADD FOREIGN...
Create an Employee table without FOREIGN KEY constraint, add some data, and try adding a FOREIGN KEY constraint using ALTER command. CREATE TABLE employee(id INT PRIMARY KEY NOT NULL, name VARCHAR(100), address VARCHAR(100), age INT, dob DATE, deptId INT); ...
Alter table to add foreign key mysql> mysql> CREATE TABLE T1 -> (A INTEGER NOT NULL PRIMARY KEY, -> B INTEGER NOT NULL); Query OK, 0 rows affected (0.00 sec) mysql> mysql> mysql> CREATE TABLE T2 -> (A INTEGER NOT NULL PRIMARY KEY, -> B INTEGER NOT NULL, -> CONSTRAINT C1 CH...
一开始拿到的是个sql文件,一心想着:只要导入sql文件,数据库中就应该有数据了吧。 但是,导入sql文件时,遇到如下错误。...[SQL] Query dailyfresh start [ERR] 1452 - Cannot add or update a child row: a foreign key con...
how to delete a foreign key which is already established by a master chid relationship.I am using the command alter table slot_week_days drop foreign key(day_code); but it is not working. it is showing the following error Error Code : 1025 ...