INTERVIEW QUESTIONS DATABASE SQL DETAILS

Question: What is the use of CASCADE CONSTRAINTS?

Answer: When this clause is used with the DROP command, a parent table can be dropped even when a child table exists.

When this clause is used with the DROP command, a parent table can be dropped even when a child table exists. Source: CoolInterview.com

For identifying the continuous constraints Source: CoolInterview.com

cascading is used for maintaining referencial integrity rules, which says that foreign key attributes values should be either subset of primary key values or null.
with cascading when parent is deleted child could be deleted/set null/set default according to cascade type.All this is for maintaing integrity. Source: CoolInterview.com

The cascade option of the drop clause causes any dependent constraints also to be dropped. Source: CoolInterview.com

we cant able to delete a record from the parent table if there is some corresponding record exists in the child table.

for this we are using cascading constraint. with the help of cascading constraint we can able to delete a record from the parent table as well as all the corresponding records from the child table.even we can set some null values. Source: CoolInterview.com

When we delete the record in parant table , the corresponding records in child table will be deleted automatically. Source: CoolInterview.com

cascade constraints describes about the parent-child relationship between tables. Source: CoolInterview.com

cascade option plays a key role in foreign and primary key table.

if record in primary key table is deleted then record in foreign key table is automatically deleted.

Source: CoolInterview.com

cascade delete means if primary key value is deleted than foreign key value is also deleted. Source: CoolInterview.com

assume that if we r using any foreign key,and because of any resion it is compulsary to delete the primary key value,for this firstly we will have to delete all value of forign key which is refering the value of primary key,it is vary tadious,to overcome with this problem we use On delete cascade or on delete null ,On delete cascade will directly remove aal the value of foreign key which is referin the value of primary key,and on delete null will put the null without deleting.
Source: CoolInterview.com

cascading is done in sql2 to maintain integrity rules in sql2 when we write cascade in a query it will tell to delete all the column which are dependent on that query row deletion Source: CoolInterview.com

The CASCADE CONSTRAINTS clause drops all
referential integrity constraints that refer to the
primary and unique keys defined on the dropped
columns Source: CoolInterview.com

The cascade option of the drop clause causes any dependent constraints also to be dropped. Source: CoolInterview.com

child record gets automatically delted when parent record is delete if on delete cascase option is used whille creating table Source: CoolInterview.com

with the help of cascading constraint we can able to delete a record from the parent table as well as all the corresponding records from the child table.even we can set some null values.
Source: CoolInterview.com

consider there are two tables and both are inter related with their keys(foreign key ) then you cannot delete parent table, by using delete cascade you can delete constraint pertaining to parent table even with existence of child table Source: CoolInterview.com

cascade constraints

is used ti change the default behavior of the foreign relation ship

if delete the record the parent table same record which is exist in the child table. that will also deleted
Source: CoolInterview.com

drop is used for deleting entire table Source: CoolInterview.com

The cascade option of the drop clause causes any dependent constraints also to be dropped.


Source: CoolInterview.com

Hi,

1-Cascade constraint is used with drop column clause.
2-Cascade constraint drops all referential integrity constraint primary key and unique key from a multicolumn table.
3-Cascade constraint also drop multicolumn constraint.

Alter table Emp
Drop (PK) cascade constraint;

Source: CoolInterview.com

when we want to delete parent table but related with child so we cant do that so we can use the casecade
Source: CoolInterview.com

cascading constraint are used to decrease the line of code and reduce the design cost. Source: CoolInterview.com

Basically Cascading constraints are use to maintain the Referencial integrity i.e. when we delete some record from parent table the correspoding data in child table should be affected. Source: CoolInterview.com

cascade constraint is used to maintain intigrity into database.so the in future do not confilct data Source: CoolInterview.com

cascade option plays a key role in foreign and primary key table for maintaining the integrity

if record in primary key table is deleted / Updated then record in foreign key table is automatically deleted / Updated.
Source: CoolInterview.com

Specify CASCADE CONSTRAINTS to drop all referential integrity constraints that refer to primary and unique keys in the dropped table. If you omit this clause, and such referential integrity constraints exist, then the database returns an error and does not drop the table. Source: CoolInterview.com

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