PostgreSQL Functions

-

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)

Comments

Post a Comment

Popular posts from this blog

PostgreSQL pg_pool-II Installation and Configuration

-
Image
Pgpool-II Pgpool-II is a proxy software that sits between PostgreSQL servers and a PostgreSQL database client.  It provides the following features: 1.Connection Pooling:     Pgpool-II maintains established connections to the PostgreSQL servers, and reuses them whenever a new connection with the same properties (i.e. user name, database, protocol version, and other connection parameters if any) comes in. It reduces the connection overhead, and improves system's overall throughput.   2.Load Balancing:     If a database is replicated (because running in either replication mode or master/slave mode), performing a SELECT query on any server will return the same result. Pgpool-II takes advantage of the replication feature in order to reduce the load on each PostgreSQL server.  It does that by distributing SELECT queries among available servers, improving the system's overall throughput. In an ideal scenario, read performance could improve proportionally to the number of PostgreSQ
Read more

PostgreSQL Migration Using MTK

-
Enterprisedb Migration Toolkit: EDB Migration Toolkit is a powerful command-line tool that offers granular control of the migration process. Migration Toolkit facilitates migration of database objects and data to an EDB Postgres Advanced Server (Advanced Server) or PostgreSQL database from: Oracle MySQL Microsoft SQL Server Sybase which objects migrate to postgres Oracle Objects: Schemas   Tables    List-Partitioned Tables         Range-Partitioned Table         Constraints   Indexes   Triggers         Table Data   Views     Materialized Views         Packages         Procedures   Functions       Sequences       Users/Roles   Profiles   Object Types   Object Type Methods   Database Links     Queues       MySQL Objects: Schemas Tables Constraints Indexes Table Data Microsoft SQL Server Objects: Schemas Tables Constraints Indexes Table Data Sybase Obj
Read more

PostgreSQL Pages and Tuples

-
Image
INTERNAL LAYOUT: a tuple or an item is a synonym for a row a relation is a synonym for a table a filenode is an id which represent a reference to a table or an index. a block and page are equals and they represent a 8kb segment information the file storing the table. a heap refer to heap file . Heap files are lists of unordered records of variable size. Although sharing a similar name, heap files are different from heap data structure. CTID represent the physical location of the row version within its table. CTID is also a special column available for every tables but not visible unless specifically mentioned. It consists of a page number and the index of an item identifier. OID stands for Object Identifier. database cluster , we call a database cluster the storage area on disk. A database cluster is a collection of databases that is managed by a single instance of a running database server. Page:            Inside the data file (heap table and index, as well as the free space ma
Read more