DBMS SQL COMMANDS

Lec - 4

create table

creates a new table
char should have max_len char(max_len)
timestamp for time

create table table_name(attr_1 data_type,
                        attr_2 data_type
                        ...
                        ...
                        );

Constraints (Field level and Table level)

primary key(TL) [not null by default]
foreign key(FL)
unique(FL)
not null(FL)
check(FL)
default(FL)

create table table_name(attr_1 data_type primary key,
                        attr_2 data_type not null,
                        attr_3 datay_type default 'default_value',
                        attr_4 data_type check(attr_4 < 100)
                        );

Some important tables

user_constraints - if we want to check the constraints
for such table values should be in UPPERCASE only
- c for check contraint
- p for primary key constraint
- u for unique constraint

select constraint_name, constraint_type from user_constraints where table_name="OUR_TABLE";

dba_ ( only sys has access )
all_ ( only sys has access )

creating a table with foreign key and creating a composite key

create table doctor(docid int primary key,
                    docname char(40) not null
                    );

create table appt(apptdate timestamp,
                  doctorid int refereces doctor(docid),
                  patid int references patient(patid),
                  primary key(appdate, doctorid, patid)  
                  );

create table visit(visitid int,
                   vdt timestamp,
                   docid int,
                   patid int,
                   foreign key(vdt, docid, patid) refereces appt(appdate, doctorid, patid));

desc table

returns the description of a table
3 cols - attr | null | type
displays not null when some fields does not allow null values

desc table_name;

drop table

deletes a table

drop table table_name;

insert

to add new data
attribute values should be in the same order

insert into table_name values(null, default, ...);

select

to view the data of some table

select * from table_name;

if some field is very large and the result is untidy we can combine attributes with ||
|| concatenates different things

select attr_1||attr_2||attr_3.. from table_name;

or we can use rtrim/ltrim/trim to remove spaces

select trim(attr_1) from table_name;

delete

to delete some data from table
deleta all the rows

delete from table_name

delete some specific rows;

delete from table_name where conditions;

update

update some record

update table_name set attr=new_value, attr_2=new_value where attr=old_value

Lec-5 and Lec-6

Generalised select statement

select distinct field/*/function/expression
from table_name/subquery
where condition_on_record_level
group by fieldnames/expression/function
having condition_on_grp/condition_on_aggregate_function
order by fieldname/expression/function

having to add condition on group
where to add condition on records
ascending by default, order by desc to change

String functions(Record based)

select  upper(patname),
	      lower(patname),
	      trim(patname),
	      rtrim(patname),           //trim empty space from right
	      ltrim(patname),
	      initcap(patname),         // First letter capital
	      substr(patname,2,2)       // From 2nd pos display 2 char 
        from patient where patid = 3;

Some conversions functions:

to_char
to _date

Date formats:

given an attribute with datatype date we can display it in the following waysL

select stdno, to_char(birtdate, 'dd') from students2021;

select stdno, to_char(birtdate, 'mm') from students2021;

select stdno, to_char(birtdate, 'yy') from students2021;

select stdno, to_char(birtdate, 'yy-mm-dd') from students2021;

select stdno, to_char(birtdate, 'month') from students2021;

select stdno, to_char(birtdate, 'dd month yyyy') from students2021;

select stdno, to_char(birtdate, 'ddth month yyyy') from students2021;

select stdno, to_char(birtdate, 'ddsp') from students2021; // spelling(sp)

Special operators(after where clause):

List(in, like, between, null/null, exists/not exists)

in

select * from patients where patid in (list...);

select * from patients where patid in (select patid from appt);

like

two wildcards

% many characters

select patname from patient where patname like 'x%' or patname like 'X%';

select patname from patient where trim(patname) like '%z' or trim(patname) like '%X';

_ single character

select patname from patient where patname like '_yz';

between

select * from patient where patid between 1 and 10; // including 1 and 10

null / not null

cannot use null with any operator so we have
- is null
- is not null

exists / not exists

returns true if any record is there else false

select * from patient where exists(select * from appnt);

Aggregate functions:

average
min
max
count
sum

select avg(field/*), min(field/*), ... ;

Joins

cross join

simple catesian product

select * from patient, appnt; //(patient * appnt)

simple / equi / natural join

Join of two tables only
Need to have one common field

select * from patient, appnt where patient.patid=appt.patid;

Multiple join

Similar to natural join, but multiple tables

select patname, docname from patient, doctor where patient.patid = appt.patid and appt.patid = doc.patid;

Inner join

similar output to natural join

select (list of fields, ... ) form table_1 inner join table_2 on table_1.common_field=table_2.common_field

Outer join

Full, left, right outer

Left Outer Join

Displays all the records of left table
- If the right table has same values in the common field, it displays the records of right table
- Else, diplays null for the right table

select * table_1 left join table_2 on common_field_condition

Right Outer Join

Null for left table, all records of right table

select * table_1 right join table_2 on common_field_condition

$\boxed{\text{left join of table1 and table2 = right join of table2 and table1}}$

Full Outer Join

Diplays both records where the values are same, left_null right_value and left_value right_null

select * table_1 right join table_2 on common_field_condition

Alias (To avoid using long table names)

select a.field_1, b.field_2 from table_1 a, table_2 b

Self Join

We will use alias to make copy of two tables
This can be useful when we want to have condition on same table( same names, diff gender ...etc )

select distinct d1.docname, d2.docid form doctor d1, doctor d2 where
(d1.docname=d2.docname) and (d1.gender <> d2.gender)

Intersection, Union, Minus

The tables should be union compatible( i.e. the number of fields should be same and should have the same type )

select (union_compatible fields, ... ) from table_1 
interset 
select (union_compatible fields, ...)  from table_2

select (union_compatible fields, ... ) from table_1 
union 
select (union_compatible fields, ...)  from table_2

select (union_compatible fields, ... ) from table_1 
minus 
select (union_compatible fields, ...)  from table_2

Group-By

select group_field, count(*) from table group by group_field

group by ... having

select group_field, count(*) from table
group by group_field
having our_condition