dbmx.txt

delete -------- (DML) - detete from table name;
delete all the entries of the row 1 by 1 so it provides - 
where clause - 
Delete from table name
where condition -------> delete row where condition is true;
basically works in O(N) time
rollback can be performed (*before commit) 
slow ----> flexible


Drop ------ (DDL) Delete whole table in cludng colums
no rollback


Truncate - delete all rows in O(1)
rollback(recycle bin) not psbl here
no where clause
faster>>>>>>>>


-----------------  constraints in SQL  -----------------
constraints are applied at column
1. Unique - only unique valu allowed(null can happened)
2. Not null - mandatory field -> something has to field
3, primary key (unique + not null) - roll no. 20205088
4. check - only some values are allowed
	e.g.  check(age > 18) - only greater 18 people are allowed

5. Foreign key - already in notes
6. Default - if we not give a value to a column
			of a particular row then it will take default

----------------------------clauses-------------
having clause only works with group by
ex - as WHERE works in row of table similarly HAVING works in groups

SELECT dept from employee group by dept having count(*) < 2
it returns - displays all the department names where employess < 2