![PostgreSQL 9
Common Table Expressions
• Basic usage
WITH [RECURSIVE] name AS
(
SELECT field1 FROM table WHERE field2=“abc”
)
SELECT * FROM name ORDER BY field;
4](https://image.slidesharecdn.com/techday2010postgresql9-13231111285291-phpapp02-111205131229-phpapp02/85/Techday2010-Postgresql9-4-320.jpg)
Techday2010 Postgresql9
- 1. What‘s new in PostgreSQL 9 Dan-Claudiu DRAGOŞ
- 2. PostgreSQL 9 About PostgreSQL • This presentation was inspired by the sessions I‘ve attended at Fosdem 2010 • PostgreSQL means: – Standards followed closely – A true relational database – Complex, advanced features that puts it far ahead of its competition – The best tool to use for advanced database-based applications! • This comes at a cost: it can‘t compete with simpler database systems on poor hardware and writing „simple things“ tends to get harder 2
- 3. PostgreSQL 9 Common Table Expressions • Available since version 8.4 • They are about defining an in-place data structure by the result of a query or a query combination • This data structure can then be queried further • Recursive join over this data structure is also possible • Some of this functionality was available before by using: • Views (named data structures stored into the database backend) • Subselects • The join recursion is a brand new feature 3
- 4. PostgreSQL 9 Common Table Expressions • Basic usage WITH [RECURSIVE] name AS ( SELECT field1 FROM table WHERE field2=“abc” ) SELECT * FROM name ORDER BY field; 4
- 5. PostgreSQL 9 Common Table Expressions • Join recursion – Assume we have the following corporate structure: -- department structure represented here is as follows: -- -- ROOT-+->A-+->B-+->C -- | | -- | +->D-+->F -- +->E-+->G – We want all the departments under A (or under any department, actually) 5
- 6. PostgreSQL 9 Common Table Expressions • Join recursion CREATE TABLE department ( id INTEGER PRIMARY KEY, parent_department INTEGER REFERENCES department, name TEXT ); INSERT INTO department (id, parent_department, "name") VALUES (0, NULL, 'ROOT'), (1, 0, 'A'), (2, 1, 'B'), (3, 2, 'C'), (4, 2, 'D'), (5, 0, 'E'), (6, 4, 'F'), (7, 5, 'G'); 6
- 7. PostgreSQL 9 Common Table Expressions • Join recursion WITH RECURSIVE subdepartment AS ( -- non-recursive term SELECT * FROM department WHERE name = 'A' UNION ALL -- recursive term SELECT d.* FROM department AS d JOIN subdepartment AS sd ON (d.parent_department = sd.id) ) SELECT * FROM subdepartment ORDER BY name; 7
- 8. PostgreSQL 9 Common Table Expressions • Join recursion – The non-recursive term is optional – There are some restrictions when it comes to defining the recursive term: – No subquery using the recursive term (no double recursion) – No aggregate functions such as COUNT(*) – No HAVING, GROUP BY – No ORDER BY, no LIMIT – No FULL JOIN – The recursive term must be on the left hand side: » JOIN reference ON (recursiveterm.field = reference.field) • The database engine performs a brute-force, all-terms comparison so performance can sometimes be an issue 8
- 9. PostgreSQL 9 Hot Standby and Streaming Replication • They are both about database synchronization • Hot Standby is a „push“ • Streaming Replication is a „pull“ • The issue at hand is duplicating the contents of a Master Database into one or more Slaves • Hot Standby means that every query ran on Master is also ran on the Slave; this also works for table locks! • Streaming replication means that every database transaction is requested by the Slave and then applied on it 9
- 10. PostgreSQL 9 Deferrable Unique Constraints • This query sequence always fails: # CREATE TABLE test (a INT PRIMARY KEY); # INSERT INTO test values (1), (2); # UPDATE test SET a = a + 1; ERROR: duplicate key value violates unique constraint "test_pkey" DETAIL: Key (a)=(2) already exists. • What 9.0 version provides is that the uniqueness constraint may be checked after running the query, not as the query runs: # CREATE TABLE test (a INT PRIMARY KEY DEFERRABLE); 10
- 11. PostgreSQL 9 Exclusion Constraints • Before 9.0, exclusion would be checked by using operator “=“ • Version 9.0 allows for a more complex approach # CREATE TABLE reservation ( room TEXT, speaker TEXT, during PERIOD); ALTER TABLE reservation ADD CONSTRAINT test_exclude EXCLUDE USING gist (room WITH =,during WITH &&); • The constraint is defined on 2 fields; the point is not having the same room reserved at the same time • The example uses 2 modules from „contrib“ (temporal and gist) 11
- 12. PostgreSQL 9 Exclusion Constraints • Example using the previous table definition: # INSERT INTO reservation (speaker ,room, during) VALUES ( ‘Dan', ‘Flex Room', period('2010-12-10 12:00:00', '2010-12-10 13:00:00')); INSERT 0 1 # INSERT INTO reservation (speaker, room, during) VALUES ( ‘Catalin', ‘Presentation', period('2010-12-10 15:00:00', '2010-12-10 16:00:00')); INSERT 0 1 # INSERT INTO reservation (speaker ,room, during) VALUES ( ‘Andrei', ‘Flex Room', period('2010-12-10 12:30:00', '2010-12-10 13:00:00')); ERROR: conflicting key value violates exclusion constraint "test_exclude" DETAIL: Key (room, during)=(Flex Room, [2010-12-10 12:30:00+02, 2010-12- 10 13:00:00+02)) conflicts with existing key (room, during)=(Flex Room, [2010-12-10 12:00:00+02, 2010-12-10 13:00:00+02)). • This feature is available in PostgreSQL only 12
- 13. Smaller enhancements • GRANT / REVOKE on Schemas – PostgreSQL has Databases -> Schemas -> Tables -> Fields – Until 9.0 you could grant (revoke) rights on Databases and Tables only – This functionality could be achieved before 9.0 by writing a script • Faster VACUUM FULL – This is the more or less equivalent to the OPTIMIZE query in MySQL – This command used to be pretty slow on large databases – In 9.0 it works by performing a copy of the database • Better 64bit support – 64bit binaries were already available on Linux – Windows native 64bit binary is the new thing in version 9.0 13
- 14. PL/PgSQL enhancements • Unnamed functions – In 9.0 you can run code snippets in place – Before 9.0 you had to define a stored procedure and then call it DO language plpgsql $$ DECLARE vr record; BEGIN FOR vr IN SELECT tablename FROM pg_tables WHERE tableowner = ‘dan' AND schemaname NOT IN ('pg_catalog','information_schema') LOOP EXECUTE 'GRANT SELECT ON ' || vr.tablename || ' TO tester'; END LOOP; END $$; 14
- 15. PL/PgSQL enhancements • Named parameter calls – Before 9.0 you had to provide all the function parameters and care for their order, as provided in the function definition – Version 8.4 added “default parameters”, allowing skipping certain parameters (they would be replaced with their default values) – Example function: CREATE FUNCTION test (a INT, b TEXT) RETURNS TEXT AS $$ DECLARE value TEXT; BEGIN value := 'a is ' || a::text || ' and b is ' || b; RETURN value; END; $$ LANGUAGE plpgsql; 15
- 16. PL/PgSQL enhancements • Named parameter calls – Before 9.0 you would have called it this way: SELECT test(1,'foo'); test ------------------------- a is 1 and b is foo (1 row) – Version 9.0 allows this type of function call: SELECT test( b:='foo', a:=1); test ------------------------- a is 1 and b is foo (1 row) 16
- 17. That’s it • Questions? 17