Asked by: Xiaofen Cabreira
technology and computing databases

Can we delete a foreign key?

24
Yes, you can. But you need to deletethe foreign key constraint first in the database.Without the relationship constraints, you can prettymuch drop the entire table containing the primarykey as there are no more dependencies. But any future ETLdata loads will not work.


In this manner, how do you drop a foreign key?

Procedure

  1. To drop foreign keys using the Control Center: Expand theobject tree until you see the Tables folder. Right-click the tableyou want to modify, and select Alter from the pop-up menu.
  2. To drop foreign keys using the command line, enter: ALTER TABLEname DROP FOREIGN KEY foreign_key_name.

Also, how do I delete a foreign key in MySQL? In MySQL, there's no DROP CONSTRAINT , you have to use DROPFOREIGN KEY instead:
  1. ALTER TABLE `table_name` DROP FOREIGN KEY `id_name_fk`;
  2. ALTER TABLE `table_name` DROP INDEX `id_name_fk`;
  3. SET FOREIGN_KEY_CHECKS=0;
  4. SET FOREIGN_KEY_CHECKS=1;

Additionally, how do I delete a foreign key in Oracle?

Oracle / PLSQL: Drop a Foreign Key

  1. Description. Once a foreign key has been created, you may findthat you wish to drop the foreign key from the table.
  2. Syntax. The syntax to drop a foreign key in Oracle/PLSQL is:ALTER TABLE table_name DROP CONSTRAINT constraint_name;
  3. Example. If you had created a foreign key as follows:

What is foreign key in database?

A foreign key is a column or group of columns ina relational database table that provides a link betweendata in two tables. It acts as a cross-reference between tablesbecause it references the primary key of another table,thereby establishing a link between them.

Related Question Answers

Madalyn Lacoste

Professional

Can foreign key be null?

A foreign key containing null valuescannot match the values of a parent key, since a parentkey by definition can have no null values.However, a null foreign key value is always valid,regardless of the value of any of its non-nullparts.

Nini Mañes

Professional

Can foreign key have duplicate values?

Unlike primary keys, foreign keys can containduplicate values. Also, it is OK for them contain NULLvalues. Indexes aren't automatically created for foreignkeys; however, as a DBA, you can define them. A table isallowed to contain more than one foreignkey.

Riva Granell

Professional

How do I remove a foreign key from a table?

To delete a foreign keyconstraint
In Object Explorer, expand the table with theconstraint and then expand Keys. Right-click the constraintand then click Delete.

Ijlal Altham

Explainer

What is difference between primary key and foreign key?

Primary key uniquely identify a record inthe table. Foreign key is a field in the tablethat is primary key in another table. By default, Primarykey is clustered index and data in the database table isphysically organized in the sequence of clustered index. Youcan manually create an index on foreign key.

Nayra Gmyrek

Explainer

Can a primary key be a foreign key?

Primary keys always need to be unique, foreignkeys need to allow non-unique values if the table is aone-to-many relationship. It is perfectly fine to use a foreignkey as the primary key if the table is connected by aone-to-one relationship, not a one-to-manyrelationship.

Estefanny Tikhobrazov

Explainer

What is composite key in SQL?

Composite key, or composite primary key,refers to cases where more than one column is used to specify theprimary key of a table. In such cases, all foreignkeys will also need to include all the columns in thecomposite key. Note that the columns that make up acomposite key can be of different data types.

Przemyslaw Ainciondo

Pundit

What is foreign key in Oracle?

A foreign key is a way to enforce referentialintegrity within your Oracle database. A foreign keymeans that values in one table must also appear in another table.The referenced table is called the parent table while the tablewith the foreign key is called the child table.

Dayane Schmettke

Pundit

What is primary key SQL?

A primary key is a field in a table whichuniquely identifies each row/record in a database table. Primarykeys must contain unique values. A primary key columncannot have NULL values. A table can have only one primarykey, which may consist of single or multiplefields.

Caleb Breton

Pundit

Can we delete a table with foreign key?

Then, forevermore, rows in the referencingtables will automatically be deleted when theirreferenced row is deleted. You can alter a foreignkey constraint with delete cascade option as shownbelow.

Simohamed Baltussen

Pundit

What is on delete cascade in SQL?

A foreign key with cascade delete means that if arecord in the parent table is deleted, then thecorresponding records in the child table will automatically bedeleted. This is called a cascade delete inSQL Server.

Sory Imroth

Pundit

How delete a row in SQL?

To remove one or more rows in a table:
  1. First, you specify the table name where you want to remove datain the DELETE FROM clause.
  2. Second, you put a condition in the WHERE clause to specifywhich rows to remove. If you omit the WHERE clause, the statementwill remove all rows in the table.

Genovaite Rancaño

Teacher

Can a database table exist without primary key?

No. Every table should have some column (or setof columns) that uniquely identifies one and only one row. It makesit much easier to maintain the data. It's true, without aprimary key (or some unique key), you don't have aninsertion anomaly if you go to insert the same data multipletimes.

Jelloul Velicu

Teacher

What is dual table Oracle?

DUAL table. From Wikipedia, the freeencyclopedia. The DUAL table is a special one-row,one-column table present by default in Oracle andother database installations. In Oracle, the tablehas a single VARCHAR2(1) column called DUMMY that has avalue of 'X'.

Joette Jakitun

Teacher

What is cascade in MySQL?

In MySQL, foreign key constraints are checkedimmediately, so NO ACTION and RESTRICT are the same.) ON DELETECASCADE causes matching child records to be deleted when thecorresponding parent record is deleted. In essence, the effect ofthe delete is cascaded from the parent to the child.

Zeinebou Villafaina

Reviewer

What are SQL constraints?

Constraints are the rules enforced on the datacolumns of a table. These are used to limit the type of data thatcan go into a table. This ensures the accuracy and reliability ofthe data in the database. Constraints could be either on acolumn level or a table level.

Drema Zumkeller

Reviewer

How do you drop a constraint?

The SQL syntax to remove a constraint from a tableis,
  1. ALTER TABLE "table_name" DROP [CONSTRAINT|INDEX]"CONSTRAINT_NAME";
  2. ALTER TABLE Customer DROP INDEX Con_First;
  3. ALTER TABLE Customer DROP CONSTRAINT Con_First;
  4. ALTER TABLE Customer DROP CONSTRAINT Con_First;

Ouafa Podury

Reviewer

What is foreign key in MySQL?

A foreign key is a field (or a set of fields) ina table that uniquely identifies a row of another table. The tablein which the foreign key is defined is called the“child table” and it (often) refers to the primarykey in the parent table.

Zhenyu Triste

Reviewer

What is a foreign key constraint?

SQL FOREIGN KEY Constraint. A FOREIGN KEYis a key used to link two tables together. A FOREIGNKEY is a field (or collection of fields) in one table thatrefers to the PRIMARY KEY in another table. The FOREIGNKEY constraint is used to prevent actions that would destroylinks between tables.

Simy Fanjul

Supporter

Can we have two foreign keys in a table in SQL Server?

Yes, MySQL allows this. You can have multiple foreignkeys on the same table. The foreign keys in yourschema (on Account_Name and Account_Type ) do not requireany special treatment or syntax. Just declare two separateforeign keys on the Customer table.

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14th June, 2020

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