[Req] Support for CREATE SEQUENCE

[ArsenShnurkov]

SQL 2003 standart introduces the way to create sequences to insert their values into PK columns.

the syntax (BNF-like) is described in ISO/IEC 9075-2:2003 (E)
paragraph 11.62

my simplified proposition:

CREATE SEQUENCE <sequence_name>
 [AS [built_in_integer_type]]
 [START WITH <constant>]
 [INCREMENT BY <constant>]

paragraph 6.13

my simplified proposition:

NEXT VALUE FOR <sequence_name>

So, to create a new record, the following sequence of SQL commands is possible:

1. Declare variable (see issue #6)
2. Generate new sequence number (to variable)
3. Insert this number into record (from variable)
4. Return this number (from variable) to the client (to EF for example)

So, what do you think about supporting this?

[ArsenShnurkov]

don't work in mariadb-10.1.9 (no CREATE SEQUENCE) and postgreql-9.4 (no NEXT VALUE FOR yet)

CREATE SEQUENCE myseq2 START WITH 1 INCREMENT BY 1;

DO $$
    DECLARE myvar2 INTEGER;
BEGIN
    SELECT NEXT VALUE FOR myseq2 INTO myvar2;
    SELECT myvar2;
END $$;

ERROR:  syntax error at or near "VALUE"
LINE 4: SELECT NEXT VALUE FOR myseq2 INTO myvar2;

(DECLARE statement don't work from script, that is why DO $$;BEGIN;END$$ is necessary:
http://www.techonthenet.com/postgresql/declare_vars.php
http://stackoverflow.com/questions/1490942/how-to-declare-a-variable-in-a-postgresql-query

Obtaining the next value is done using the nextval() function instead of the standard's NEXT VALUE FOR expression, from http://www.postgresql.org/docs/current/static/sql-createsequence.html
)