Sunday, August 4, 2013

New in PostgreSQL 9.3: New in Functions

In the series of blogging about new features in 9.3, today, I thought about blogging new functions and improvements coming in PostgreSQL.
Lets look whats new in 9.3, in terms of in build functions:

1. New in one array functions for one dimensional array
PostgreSQL 9.3, is coming with new functions which can help users to manipulate one dimensional arrays by calling simple functions at the place of crafting their own functions and following some methods to do the modification in it.

i. array_remove function

This is a new function added in 9.3, which provides ability for removing the elements from array. Function takes two arguments:

  a. One dimensional array from which user wants to remove elements 
 b. element value which user wants to remove .

Syntax of this function is given below:
  
ARRAY_REMOVE(, element)

Example of array_remove is given below:
  
postgres=# select array_remove(ARRAY['First','Second','Delete','Four'],'Delete');
    array_remove     
---------------------
 {First,Second,Four}
(1 row)


ii. array_replace function

This is a new in 9.3, this helps user to replace any element in array. This function can be use multi-dimensional array Or for single dimensional array. Example of array_replace is given below:
  
pgsqltest=# select array_replace(ARRAY[ARRAY[1,2],ARRAY[3,4],ARRAY[56,6],ARRAY[7,8]],56,5);
       array_replace       
---------------------------
 {{1,2},{3,4},{5,6},{7,8}}
(1 row)


2. VARIADIC-labeled arguments expansion for concat and format functions

This is new addition to concat and format function. pre-9.3 concat and format, function used to ignore VARIADIC label and doesn't used to print right output. However, this has been fixed in 9.3. Lets look at the example of pre-9.3 and in 9.3

In pre-9.3
  
worktest=# select concat(variadic array[1,2,3]);
 concat  
---------
 {1,2,3}
(1 row)

In 9.3
  
pgsqltest=# select concat(variadic array[1,2,3]);
 concat 
--------
 123
(1 row)

You can see above in 9.3, using VARIADIC label working properly.

Lets look at the format() function:

In pre-9.3
  
worktest=# select format(string_agg('%s',','), variadic array_agg(i)) from generate_series(1,3) g(i);
ERROR:  too few arguments for format

woow, its error out. However, this is fixed in 9.3 :-).

In 9.3
  
pgsqltest=# select format(string_agg('%s',','), variadic array_agg(i)) from generate_series(1,3) g(i);
 format 
--------
 1,2,3
(1 row)


3. Improvement in format() function to handle field width and left/right alignment
This new added in 9.3 format() function, which is going to increase the usability of format() function for developers.
In 9.3, format function is coming with following enhancements:
 i). Proper handling of field width.
ii). Proper handling of Left/right alignment.

Above two improvement was missing in pre-9.3. However, addition of above improvement made format() function to be follower of sprintf() C function.
Lets look at the example:

In pre-9.3, using of field width resulted into error message, as given below
  
ERROR:  unterminated conversion specifier
worktest=#  select format('>>%10s<<', 'Hello');
ERROR:  unterminated conversion specifier
worktest=# 


However, 9.3 is coming with proper field width support.
  
pgsqltest=#  select format('>>%10s<<', 'Hello');
     format     
----------------
 >>     Hello<<
(1 row)

9.3 is also coming proper handling left/right alignment. Examples are given below:

Left alignment
  
pgsqltest=# select format('>>%-10s<<', 'Hello');
     format     
----------------
 >>Hello     <<
(1 row)

Right alignment
  
pgsqltest=# select format('>>%1$10s<<', 'Hello');
     format     
----------------
 >>     Hello<<
(1 row)



4. Proper handling of Negative century in to_char, to_date and to_timestamp functions

In pre-9.3, following function behavior for negative century was wrong or inconsistent a. to_char b. to_date c. to_timestamp.

However, 9.3 is coming with proper fix/handling for negative century. Lets look at the output in pre-9.3 and in 9.3 for each functions.

pre-9.3
  
worktest=# select to_timestamp('4713-01-08 BC','YYYY-DD-MM bc');
         to_timestamp         
------------------------------
 01-AUG-13 00:00:00 -04:56:02
(1 row)


Above you can see that its displaying wrong result for BC.

In 9.3
  
pgsqltest=# select to_timestamp('4713-01-08 BC','YYYY-DD-MM bc');
          to_timestamp           
---------------------------------
 4713-08-01 00:00:00-04:56:02 BC
(1 row)

Lets see for to_date functions.

In 9.2/pre-9.3
  
worktest=# SELECT to_date('4713-01-08 BC','YYYY-DD-MM bc');
ERROR:  full year must be between -4712 and +9999, and not be 0
worktest=# 

In 9.3
  
pgsqltest=# SELECT to_date('4713-01-08 BC','YYYY-DD-MM bc');
    to_date    
---------------
 4713-08-01 BC
(1 row)

Above, you can see in 9.3,to_date function is working right. However to_date in 9.2 didn't able to handle it. Similar behavior you can see for to_char function.

5. Improvement in pg_get_viewdef() to print new line after each SELECT and FROM entry

This is kind of enhancement made in pg_get_viewdef function of 9.3. And user will be able to see this enhancement in pg_dump plain dump too.

This enhancement is more like readability of output of view definition in 9.3 and reducing the line length of view definition. Lets look at how this improvement makes user experience of getting/viewing view definition much better.

Before 9.3 or in pre-9.3
  
worktest=# select pg_get_viewdef('pg_tables'::regclass);
                                                                                                    
                                                                                  pg_get_viewdef    
                                                                                                    
                                                                              
----------------------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------------------
------------------------------------------------------------------------------
 SELECT n.nspname AS schemaname, c.relname AS tablename, pg_get_userbyid(c.relowner) AS tableowner, 
t.spcname AS tablespace, c.relhasindex AS hasindexes, c.relhasrules AS hasrules, c.relhastriggers AS
 hastriggers FROM ((pg_class c LEFT JOIN pg_namespace n ON ((n.oid = c.relnamespace))) LEFT JOIN pg_
tablespace t ON ((t.oid = c.reltablespace))) WHERE (c.relkind = 'r'::"char");
(1 row)


Above you can see that pg_get_viewdef has printed defintion of view in one line, which not only make readability of view definition difficult. However also increase the line length.

Lets look at the pg_get_viewdef in 9.3
  
pgsqltest=# select pg_get_viewdef('pg_tables'::regclass);
                        pg_get_viewdef                        
--------------------------------------------------------------
  SELECT n.nspname AS schemaname,                            +
     c.relname AS tablename,                                 +
     pg_get_userbyid(c.relowner) AS tableowner,              +
     t.spcname AS tablespace,                                +
     c.relhasindex AS hasindexes,                            +
     c.relhasrules AS hasrules,                              +
     c.relhastriggers AS hastriggers                         +
    FROM ((pg_class c                                        +
    LEFT JOIN pg_namespace n ON ((n.oid = c.relnamespace)))  +
    LEFT JOIN pg_tablespace t ON ((t.oid = c.reltablespace)))+
   WHERE (c.relkind = 'r'::"char");
(1 row)


which seems me better in terms of readability and doesn't have long line.

Enjoy!!

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