PostgreSQL Functions

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Build-in Functions:


  • Aggregate functions
  • Scalar Functions

Aggregate Functions:

Examples:
pearl=# select * from siva ;
 id |   name   | age | salary
----+----------+-----+--------
  1 | muthu    |  21 |   2000
  2 | siva     |  26 |   4000
  3 | thanigai |  27 |   5000
  4 | chandru  |  28 |   2000
  5 | kathir   |  27 |   3000
(5 rows)

pearl=# select max(age) from siva;
 max
-----
  28
(1 row)

pearl=# select min(age) from siva;
 min
-----
  21
(1 row)

pearl=# select avg(salary) from siva;
          avg         
-----------------------
 3200.0000000000000000
(1 row)

pearl=# select count(id) from siva;
 count
-------
     5
(1 row)

pearl=# select sum(salary) from siva;
  sum 
-------
 16000
(1 row)

pearl=# select * from siva order by salary;
 id |   name   | age | salary
----+----------+-----+--------
  1 | muthu    |  21 |   2000
  4 | chandru  |  28 |   2000
  5 | kathir   |  27 |   3000
  2 | siva     |  26 |   4000
  3 | thanigai |  27 |   5000
(5 rows)

pearl=# select * from siva order by salary desc;
 id |   name   | age | salary
----+----------+-----+--------
  3 | thanigai |  27 |   5000
  2 | siva     |  26 |   4000
  5 | kathir   |  27 |   3000
  1 | muthu    |  21 |   2000
  4 | chandru  |  28 |   2000
(5 rows)

pearl=# select age from siva group by age;
 age
-----
  26
  21
  28
  27
(4 rows)

pearl=# select age from siva group by age having age=27;
 age
-----
  27
(1 row)

Scalar Functions:

date functions:

pearl=# select age(timestamp '2001-04-10', timestamp '1957-06-13');
           age         
-------------------------
 43 years 9 mons 27 days
(1 row)

pearl=# select age(timestamp '2001-04-10');
           age         
-------------------------
 19 years 3 mons 18 days
(1 row)

pearl=# select clock_timestamp();
         clock_timestamp         
----------------------------------
 2020-07-28 11:58:29.142519+05:30
(1 row)

pearl=# select current_date;
 current_date
--------------
 2020-07-28
(1 row)

pearl=# select current_time;
     current_time     
-----------------------
 11:58:53.033972+05:30
(1 row)

pearl=# select current_timestamp;
        current_timestamp       
---------------------------------
 2020-07-28 11:58:57.95539+05:30
(1 row)

pearl=# select date_part('hour', timestamp '2001-02-16 20:38:40');
 date_part
-----------
        20
(1 row)

pearl=# select date_part('month', interval '2 years 3 months');
 date_part
-----------
         3
(1 row)

pearl=# select date_trunc('hour', timestamp '2001-02-16 20:38:40');
     date_trunc     
---------------------
 2001-02-16 20:00:00
(1 row)

pearl=# select date_trunc('hour', interval '2 days 3 hours 40 minutes');
   date_trunc   
-----------------
 2 days 03:00:00
(1 row)

pearl=# select  localtime;
    localtime   
-----------------
 12:03:06.762483
(1 row)

pearl=# select localtimestamp;
      localtimestamp     
---------------------------
 2020-07-28 12:03:17.96969
(1 row)

pearl=# select make_date(2013, 7, 15);
 make_date 
------------
 2013-07-15
(1 row)

pearl=# select make_time(8, 15, 23.5);
 make_time 
------------
 08:15:23.5
(1 row)

pearl=# select make_timestamp(2013, 7, 15, 8, 15, 23.5);
    make_timestamp   
-----------------------
 2013-07-15 08:15:23.5
(1 row)

pearl=# select now();
               now               
----------------------------------
 2020-07-28 12:04:34.995758+05:30
(1 row)

pearl=# select statement_timestamp();
       statement_timestamp       
----------------------------------
 2020-07-28 12:04:54.696116+05:30
(1 row)

pearl=# select timeofday();
              timeofday             
-------------------------------------
 Tue Jul 28 12:05:13.588796 2020 IST
(1 row)

pearl=# select transaction_timestamp();
      transaction_timestamp     
----------------------------------
 2020-07-28 12:05:57.968226+05:30
(1 row)

pearl=# SELECT to_date('20170103','YYYYMMDD');
  to_date 
------------
 2017-01-03
(1 row)

pearl=# SELECT TO_TIMESTAMP('2017-03-31 9:30:20','YYYY-MM-DD HH:MI:SS');
       to_timestamp       
---------------------------
 2017-03-31 09:30:20+05:30
(1 row)

numeric functions:

pearl=# select abs(5);
 abs
-----
   5
(1 row)

pearl=# select abs(-5);
 abs
-----
   5
(1 row)

pearl=# select ceil(7.43);
 ceil
------
    8
(1 row)

pearl=# select ceiling(7.43);
 ceiling
---------
       8
(1 row)

pearl=# select floor(7.43);
 floor
-------
     7
(1 row)

pearl=# select greatest(4,3,5,6,2,8,1);
 greatest
----------
        8
(1 row)

pearl=# select least(4,3,5,6,2,8,1);
 least
-------
     1
(1 row)

pearl=# select mod(15,4);
 mod
-----
   3
(1 row)

pearl=# select pi();
        pi       
------------------
 3.14159265358979
(1 row)

pearl=# select power(4,4);
 power
-------
   256
(1 row)

pearl=# select pow(4,4);
 pow
-----
 256
(1 row)

pearl=# select round(6.68456);
 round
-------
     7
(1 row)

pearl=# select round(6.68456,2);
 round
-------
  6.68
(1 row)

pearl=# select trunc(123.9);
 trunc
-------
   123
(1 row)

pearl=# select sqrt(81);
 sqrt
------
    9
(1 row)

string functions:

pearl=# select ascii('A');
 ascii
-------
    65
(1 row)

pearl=# select char_length('muthu');
 char_length
-------------
           5
(1 row)

pearl=# select length('siva');
 length
--------
      4
(1 row)


pearl=# select concat('muthu','siva');
  concat 
-----------
 muthusiva
(1 row)

pearl=# select concat_ws(',','first_name','second_name');
       concat_ws       
------------------------
 first_name,second_name
(1 row)

pearl=# select left('muthusiva',5);
 left 
-------
 muthu
(1 row)
pearl=# select right('muthusiva',4);
 right
-------
 siva
(1 row)

pearl=# select lower('MUTHU');
 lower
-------
 muthu
(1 row)

pearl=# select upper('muthu');
 upper
-------
 MUTHU
(1 row)

pearl=# select ltrim(' siva');
 ltrim 
--------
 siva
(1 row)

pearl=# select rtrim('siva ');
 rtrim
-------
 siva
(1 row)

pearl=# select trim('  siva   ');
 btrim
-------
 siva
(1 row)

pearl=# select trim(leading 'x' from 'xxxsivaxxx');
  ltrim 
---------
 sivaxxx
(1 row)

pearl=# select trim(both 'x' from 'xxxsivaxxx');
 btrim
-------
 siva
(1 row)

pearl=# select trim(trailing 'x' from 'xxxsivaxxx');
  rtrim 
---------
 xxxsiva
(1 row)

pearl=# SELECT REGEXP_SPLIT_TO_ARRAY('muthu siva', E'\\s+');
 regexp_split_to_array
-----------------------
 {muthu,siva}
(1 row)

pearl=# SELECT REGEXP_SPLIT_TO_TABLE('muthu siva', E'\\s+');
 regexp_split_to_table
-----------------------
 muthu
 siva
(2 rows)

pearl=# select repeat('siva',3);
    repeat   
--------------
 sivasivasiva
(1 row)

pearl=# select replace('muthu siva','muthu','pearl');
  replace 
------------
 pearl siva
(1 row)

pearl=# select reverse('avisuhtum');
  reverse 
-----------
 muthusiva
(1 row)

pearl=# select rpad('muthu',10,'*');
    rpad   
------------
 muthu*****
(1 row)

pearl=# select lpad('muthu',10,'*');
    lpad   
------------
 *****muthu
(1 row)

pearl=# select substring('iammuthusiva',4);
 substring
-----------
 muthusiva
(1 row)

pearl=# select substring('iammuthusiva' from 4);
 substring
-----------
 muthusiva
(1 row)

pearl=# select substring('iammuthusiva',4,5);
 substring
-----------
 muthu
(1 row)

conversion functions:

pearl=# select to_char(current_timestamp, 'HH12:MI:SS');
 to_char 
----------
 12:55:02
(1 row)

pearl=# select to_char(interval '15h 2m 12s', 'HH24:MI:SS');
 to_char 
----------
 15:02:12
(1 row)

pearl=# select to_char(125, '999');
 to_char
---------
  125
(1 row)

pearl=# select to_date('05 Dec 2000', 'DD Mon YYYY');
  to_date 
------------
 2000-12-05
(1 row)

pearl=# select to_number('12,454.8-', '99G999D9S'); //visite https://www.postgresqltutorial.com/postgresql-to_number/
 to_number
-----------
  -12454.8
(1 row)

pearl=# select to_timestamp('05 Dec 2000', 'DD Mon YYYY');
       to_timestamp       
---------------------------
 2000-12-05 00:00:00+05:30
(1 row)

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