Database Technologies

There is always discussion of having UPSERT/MERGE in postgresql. Since, oracle and other RDBMS has this feature, therefore people ask about this feature in PostgeSQL. In previous version of PostgreSQL, we used to implement it using functions. Now in PostgreSQL 9.1, user can implement this feature using Writable CTE. PostgreSQL 9.1, now has Writable CTE using WTH. WITH provides a way to write auxiliary statements for use in a larger query. These statements, which are often referred to as Common Table Expressions or CTEs, can be thought of as defining temporary tables that exist just for one query. Each auxiliary statement in a WITH clause can be a SELECT, INSERT, UPDATE, or DELETE; and the WITH clause itself is attached to a primary statement that can also be a SELECT, INSERT, UPDATE, or DELETE. Lets see how we can use Writable CTE for UPSERT. Following are SQL Code which can be use in Oracle and PostgreSQL for creating sample data: For oracle: create table myTable (pid numb

1. SQL function format(text, …):  This function is similar to the C function sprintf; However only the following conversion specifications are recognized: %s interpolates the corresponding argument as a string %I escapes its argument as an SQL identifier %L escapes its argument as an SQL literal %% outputs a literal %. A conversion can reference an explicit parameter position by preceding the conversion specifier with n$, where n is the argument position Some Examples are given below: postgres=# select format('%1$s %3$s', 1, 2, 3); format -------- 1 3 (1 row) postgres=# select format('Hello %s', 'World'); format ------------- Hello World (1 row) postgres=# select format('Hello %s %1$s %s', 'World', 'Hello again'); format ------------------------------- Hello World World Hello again (1 row) 2. New string functions concat(), concat_ws(), left(), right(), and reverse() (i). concat() function:

1. pg_describe_object:  In PostgreSQL 9.1, pg_describe_object function has been added. Using this function, user can get human readable string for understanding the pg_depend content as given below: postgres=# select classid, objid, objsubid, pg_describe_object(classid, objid, objsubid) from pg_depend where classid <> 0 and pg_describe_object(classi classid | objid | objsubid | pg_describe_object ---------+-------+----------+------------------------------------------------ 1247 | 16426 | 0 | type test_money 1247 | 16425 | 0 | type test_money[] 1259 | 16424 | 0 | table test_money 1259 | 16429 | 0 | index test_money_idx 2606 | 16431 | 0 | constraint uniq_constraint on table test_money 2. quote_all_identifiers (boolean) parameter:  With this parameter, User can force quoating of all identifiers in EXMPLAIN and in system catalog functions like pg_get_viewdef(). Example is given below: postgr

PostgreSQL 9.1 has come with new options and Improvement for Client Application. So, I thought to blog about those improvements.   Deprecated createlang/droplang: In PostgreSQL 9.1, createlang/dronlang is now deprecated commands. Since in PostgreSQL 9.1, for creating additional language, user has to use CREATE EXTENSION SYNTAX , there these binaries now issue command given below: CREATE EXTENSION plperl; CREATE EXTENSION plpyhthon; Added Features in psql: In PostgreSQL 9.1, following are the important improvement done in psql command:   1. Know about connection. Now psql has meta command \conninfo which gives detal about current connections. So, if you are connected to PostgreSQL database, then you can use command "\conninfo" to get detail about your connections, some example is given below: postgres=# \conninfo You are connected to database "postgres" as user "postgres" via socket in "/tmp" at port "5432". postgres=# \conni