Getting Started with PostgreSQL :
https://dev117uday.gitbook.io/databases/sql/getting-started
Loading Sample Data Guide :
https://dev117uday.gitbook.io/databases/sql/getting-started/load-data
Internal Functions
Order of execution of SQL statements
- FROM
- WHERE
- SELECT
- ORDER BY
Concatenation Operator
select concat(first_name,last_name) as full_name
from directors limit 10;
full_name
----------------
TomasAlfredson
PaulAnderson
WesAnderson
select concat_ws(' ',first_name,last_name) as full_name
from directors limit 3;
full_name
-----------------
Tomas Alfredson
Paul Anderson
Wes Anderson
- if you can have a null value in column, always use
concat_wsbecause it will place nothing in that and and also not place the spacer like | or a space
Type Conversion
| Type of Conversion | Notes |
|---|---|
| Implicit | data conversion is done AUTOMATICALLY |
| Explicit | data conversion is done via 'conversion functions' eg. CAST or ::
|
SELECT * FROM movies;
-- exact datatype match : no conversion
SELECT * FROM movies WHERE movie_id = 1;
-- Implicit conversion : conversion
SELECT * FROM movies WHERE movie_id = '1';
-- Explicit conversion : conversion
SELECT * FROM movies WHERE movie_id = integer '1';
-- Output of all queries above
movie_id | movie_name | movie_length | movie_lang | release_date | age_certificate | director_id
----------+--------------------+--------------+------------+--------------+-----------------+-------------
1 | A Clockwork Orange | 112 | English | 1972-02-02 | 18 | 13
Casting
-- CAST function
-- Syntax : CAST ( expression as target_data_type );
SELECT CAST ( '10' AS INTEGER );
int4
------
10
SELECT
CAST ('2020-02-02' AS DATE),
CAST('01-FEB-2001' AS DATE);
date | date
------------+------------
2020-02-02 | 2001-02-01
SELECT
CAST ( 'true' AS BOOLEAN ),
CAST ( '1' AS BOOLEAN ),
CAST ( '0' AS BOOLEAN );
bool | bool | bool
------+------+------
t | t | f
SELECT CAST ( '14.87789' AS DOUBLE PRECISION );
float8
----------
14.87789
SELECT '2020-02-02'::DATE , '01-FEB-2001'::DATE;
date | date
------------+------------
2020-02-02 | 2001-02-01
SELECT '2020-02-02 10:20:10.23'::TIMESTAMP;
timestamp
------------------------
2020-02-02 10:20:10.23
SELECT '2020-02-02 10:20:10.23 +05:30'::TIMESTAMPTZ;
timestamptz
---------------------------
2020-02-02 04:50:10.23+00
SELECT
'10 minute'::interval,
'10 hour'::interval,
'10 day'::interval,
'10 week'::interval,
'10 month'::interval;
interval | interval | interval | interval | interval
----------+----------+----------+----------+----------
00:10:00 | 10:00:00 | 10 days | 70 days | 10 mons
SELECT
20! AS "result 1" ,
CAST( 20 AS bigint ) ! AS "result 2";
result 1 | result 2
---------------------+---------------------
2432902008176640000 | 2432902008176640000
SELECT
ROUND(10,4) AS "result 1",
ROUND ( CAST (10 AS NUMERIC) ) AS "result 2",
ROUND ( CAST (10 AS NUMERIC) , 4 ) AS "result 3";
result 1 | result 2 | result 3
----------+----------+----------
10.0000 | 10 | 10.0000
SELECT
SUBSTR('12345',2) AS "RESULT 1",
SUBSTR( CAST('12345' AS TEXT) ,2) AS "RESULT 2";
RESULT 1 | RESULT 2
----------+----------
2345 | 2345
CREATE TABLE ratings (
rating_id SERIAL PRIMARY KEY,
rating VARCHAR(2) NOT NULL
);
INSERT INTO ratings ( rating )
VALUES ('A'), ('B'), ('C'), ('D'), (1), (2), (3), (4);
SELECT
rating_id,
CASE
WHEN rating~E'^\\d+$' THEN
CAST ( rating as INTEGER )
ELSE
0
END AS rating
FROM
ratings;
rating_id | rating
-----------+--------
1 | 0
2 | 0
3 | 0
4 | 0
5 | 1
6 | 2
7 | 3
8 | 4
Formatting Functions
https://www.postgresql.org/docs/12/functions-formatting.html
to_char()
Refer to the documentation
SELECT TO_CHAR (
100870,
'9,999999'
);
to_char
-----------
100870
SELECT
release_date,
TO_CHAR(release_date,'DD-MM-YYYY'),
TO_CHAR(release_date,'Dy, MM, YYYY')
FROM
movies LIMIT 3;
release_date | to_char | to_char
--------------+------------+---------------
1972-02-02 | 02-02-1972 | Wed, 02, 1972
1979-08-15 | 15-08-1979 | Wed, 08, 1979
2001-01-04 | 04-01-2001 | Thu, 01, 2001
SELECT
TO_CHAR (
TIMESTAMP '2020-01-01 13:32:30',
'HH24:MI:SS'
);
to_char
----------
13:32:30
to_number()
SELECT TO_NUMBER(
'1420.89', '9999.'
);
to_number
-----------
1420
SELECT TO_NUMBER(
'10,625.78-', '99G999D99S'
);
to_number
-----------
-10625.78
SELECT TO_NUMBER(
'$1,625.78+', '99G999D99S'
);
to_number
-----------
1625.78
SELECT to_number(
'$1,420.65' , 'L9G999D99'
);
to_number
-----------
1420.65
SELECT to_number(
'21,420.65' , '99G999D99'
);
to_number
-----------
21420.65
to_date()
SELECT TO_DATE( '2020/10/22' , 'YYYY/MM/DD' );
to_date
------------
2020-10-22
SELECT to_date( '022199' , 'MMDDYY' );
to_date
------------
1999-02-21
SELECT to_date( 'March 07, 2019' , 'Month DD, YYYY' );
to_date
------------
2019-03-07
to_timestamp()
SELECT TO_TIMESTAMP(
'2017-03-31 9:30:20',
'YYYY-MM-DD HH:MI:SS'
);
to_timestamp
------------------------
2017-03-31 09:30:20+00
SELECT
TO_TIMESTAMP('2017 Aug','YYYY MON');
to_timestamp
------------------------
2017-08-01 00:00:00+00
String Functions
-
Upper(string) Lower(string)INITCAP(string)REVERSE(string)LPAD(string)RPAD(string)LENGTH(string)CHAR_LENGTH(string) : Same as LengthPOSITION( string in string )STRPOS ( , < substring > )SUBSTRING (string , length)-
REPLACE (string, from_string, to_string)
SELECT INITCAP(first_name) as FirstName,
INITCAP(last_name) as LastName
FROM directors
LIMIT 3;
firstname | lastname
-----------+-----------
Tomas | Alfredson
Paul | Anderson
Wes | Anderson
SELECT LEFT('Uday', 3), RIGHT('Uday', 3);
left | right
------+-------
Uda | day
SELECT LEFT('Uday', -3), RIGHT('Uday', -3);
left | right
------+-------
U | y
SELECT REVERSE('UDAY YADAV');
reverse
------------
VADAY YADU
SELECT SPLIT_PART('1,2,3,4', ',', 1),
SPLIT_PART('1|2|3|4', '|', 2);
split_part | split_part
------------+------------
1 | 2
SELECT TRIM(LEADING FROM ' Amazing PostgreSQL'),
TRIM(TRAILING FROM 'Amazing PostgreSQL '),
TRIM(' Amazing PostgreSQL ');
ltrim | rtrim | btrim
--------------------+--------------------+--------------------
Amazing PostgreSQL | Amazing PostgreSQL | Amazing PostgreSQL
SELECT TRIM(LEADING '0' FROM CAST(0001245 AS TEXT));
ltrim
-------
1245
SELECT LTRIM('yummy', 'y'),
RTRIM('yummy', 'y'),
BTRIM('yummy', 'y');
ltrim | rtrim | btrim
-------+-------+-------
ummy | yumm | umm
SELECT upper('uday yadav'), initcap('uday yadav');
upper | initcap
------------+------------
UDAY YADAV | Uday Yadav
SELECT INITCAP(first_name) as FirstName,
INITCAP(last_name) as LastName
FROM directors LIMIT 3;
firstname | lastname
-----------+-----------
Tomas | Alfredson
Paul | Anderson
Wes | Anderson
SELECT LEFT('Uday', 3), RIGHT('Uday', 3);
left | right
------+-------
Uda | day
SELECT LEFT('Uday', -3), RIGHT('Uday', -3);
left | right
------+-------
U | y
SELECT LPAD('Database', 15, '*'),
RPAD('Database', 15, '*');
lpad | rpad
-----------------+-----------------
*******Database | Database*******
SELECT LENGTH('Uday Yadav');
length
--------
10
SELECT LENGTH(CAST(10013 AS TEXT));
length
--------
5
SELECT char_length(''),
char_length(' '),
char_length(NULL);
char_length | char_length | char_length
-------------+-------------+-------------
0 | 2 |
SELECT first_name || ' ' || last_name as FullName,
LENGTH(first_name || ' ' || last_name)
as FullNameLength
FROM Directors
ORDER BY 2 DESC LIMIT 2;
fullname | fullnamelength
-----------------------------------+----------------
Florian Henckel von Donnersmarck | 33
Francis Ford Coppola | 20
SELECT POSITION('Amazing' IN 'Amazing PostgreSQL'),
POSITION('is' IN 'This is a computer');
position | position
----------+----------
1 | 3
SELECT STRPOS('World Bank', 'Bank');
strpos
--------
7
SELECT first_name,
last_name
FROM directors
WHERE strpos(last_name, 'on') > 0 LIMIT 3;
first_name | last_name
------------+-----------
Tomas | Alfredson
Paul | Anderson
Wes | Anderson
SELECT substring('What a wonderful world' from 1 for 10);
substring
------------
What a won
SELECT repeat('A', 4), repeat(' ', 9), repeat('.', 8);
repeat | repeat | repeat
--------+-----------+----------
AAAA | | ........
SELECT REPLACE('ABC XYZ', 'XY', 'Z');
replace
---------
ABC ZZ
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