sql -interview question-part-02

 Sql interview questions:


1)what is sql?


2)what are the subsets of sql?


ddl 

(creaet,alter,drop,truncate,rename)

dml(dekete update,insert)

dcl(grant,revoke)

tcl(commit,roolback,savepoint)



3)create table and add data


4)difference between truncate ,drop and delete in sql?


truncate table:


truncate table table

-name


drop 


drop table table_name


select*from table name delete where id ='10';


5).what are constrains in sql?


primary key

foreign key

not null

default

check

unique


6).difference between primary key and foreign key:


primary key:


its doesn't accept the null value

only one primary key it will be there


unique key:


accept the null values

many unique keys are there



7).Difference between union and union all?


union : removes any duplicates records.


union all: its doesn't remove duplicate records


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