ALTER COMMAND IN SQL || DDL COMMANDS || SQL COMMANDS || ALTER DATABASE || MYSQL || DBMS

ALTER COMMAND IN SQL

- DDL COMMAND

- To change the shcema / Structure of database

* Add Column
* Delete Column
* Modify datatype of existing column
* Set constraints like NOT NULL, PRIMARY KEY, UNIQUE KEY etc..
* Remove constraints
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ADD COLUMN

alter table table_name
add column_name datatype

DROP COLUMN

alter table table_name
drop column column_name

MODIFY DATATYPE

alter table table_name
modify column column_name datatype

ADD NOT NULL

alter table table_name
modify column_name datatype NOT NULL

ADD CONSTRAINT UNIQUE

alter table table_name
add constraint unique(column_name)

ADD PRIMARY KEY CONSTRAINT

alter table table_name
add constraint primary key(column_name)

ADD CONSTRAINT CHECK

alter table table_name
add constraint check(condition)

DROP CONSTRAINT PRIMARY KEY

alter table table_name
drop primary key

DROP CONSTRAINT UNIQUE

alter table table_name
drop index column_name

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[jeevithaloknath]

Sir, You really explain well in a simple manner. I refer your videos even for the Python Programs and learnt a lot.

[hasanmougharbel]

Hey my friend, blessed to discover your channel.
I have only a simple enquiry as a newbie sql learner.
What is the main difference between alter and update in terms of their application in sql?
Thanks for taking time on this..

[chevalasudharani]

Hi sir, your explanation is good. While I am using not null constraint iam getting error invalid use of null value. Can you please suggest me.

[sukumarkothapally]

Sir please explain select(DQL) with all the conditions and clauses

[Mahboob_Creative_Arts]

Hello Sir,

Can we update a column name in a table on top of data type instead of removing and adding it again ? For example, I have column name as "EmployID" hence I want to change it "Employee_ID".

[hemandh]

how to delete check and default constraints?