Postgresql 9.3 overview

1. PostgreSQL 9.3
overview

2. Schemas
SQL
CREATE SCHEMA schema;
schema.table
database.schema.table
CREATE TABLE myschema.table ( … );
DROP SCHEMA myschema CASCADE;
SHOW search_path;
SET search_path TO myschema, public;
SHOW search_path;
search_path
text
"$user",public
search_path
text
myschema, public

3. Data types: Usual
Numeric
Name Storage size Description Range
smallint 2 bytes small-range integer -32768 to +32767
integer 4 bytes typical choice for integer -2147483648 to 2147483647
bigint 8 bytes large-range integer -9223372036854775808 to -9223372036854775807
decimal, numeric variable user-specified precision, exact to 131072 digits before the point; up to 16383 digits after the point
real 4 bytes variable-precision, inexact 6 decimal digits precision
double precision 8 bytes variable-precision, inexact 15 decimal digits precision
Char
Name Description
character varying(n), varchar(n) variable-length with limit
character(n), char(n) fixed-length, blank padded
text variable unlimited length
Temporal
Name B Description Low Value High Value Resolution
timestamp [(p)] [without time zone] 8 both date and time (no tz) 4713 BC 294276 AD 1 microsec/14 digits
timestamp [(p)] with time zone 8 both date and time, with tz 4713 BC 294276 AD 1 microsec/14 digits
date 4 date (no time of day) 4713 BC 5874897 AD 1 day
time [(p)] [without time zone] 8 time of day (no date) 00:00:00 24:00:00 1 microsec/14 digits
time [(p)] with time zone 12 times of day only, with tz 00:00:00+1459 24:00:00-1459 1 microsec/14 digits
interval [fields] [(p)] 12 time interval -178000000 years 178000000 years 1 microsec/14 digits
Enum
Other
Type Size Description
money 8 currency amount (lc_monetary)
boolean 1 true/false
bytea 1-* variable length binary string
CREATE TYPE status_enum AS ENUM (‘pending’, ‘in_progress’, ‘done’);
CREATE TABLE tbl_order (id bigserial, status status_enum);
INSERT INTO tbl_order VALUES (1, ‘pending’);

4. Data types: Special
Geometric
Name Storage size Representation Description
point 16 bytes Point on a plane (x,y)
line 32 bytes Infinite line (not fully implemented) ( (x1,y1), (x2,y2) )
lseg 32 bytes Finite line segment ( (x1,y1), (x2,y2) )
box 32 bytes Rectangular box ( (x1,y1), (x2,y2) )
path 16 + 16n bytes Closed path (similar to polygon) ( (x1,y1), … )
path 16 + 16n bytes Open path [ (x1,y1), … ]
polygon 40 + 16n bytes Polygon (similar to open path) ( (x1,y1), … )
circle 24 bytes Circle < (x,y), r >
Network
Name B Description
cidr 7 or 19 bytes IPv4 and IPv6 networks
inet 7 or 19 bytes IPv4 and IPv6 hosts and networks
macaddr 6 bytes MAC addresses
UUID
SELECT a0eebc99-9c0b-4ef8-bb6d-6bb9bd380a11
Bits
Name Size Example
bit (n) n B’101’
bit varying (n) n B’1000101’
Name
ts_vector
ts_query
TextSearch

5. Data types: Arrays
SQL
CREATE TABLE test_arrays (
usual integer[], usual_dim integer[4],
nested text[][], nested_dim integer[3][3],
ansi_sql integer ARRAY, ansi_sql_dim integer ARRAY[4]
);
SELECT ‘{1,2,3}’, ARRAY[1,2,3], ‘{ {1,2,3}, {4,5,6} }’, ARRAY[ [1,2,3], [4,5,6] ];
SELECT '{1,2,3}'::int[][1]; -- outputs: 1, since indeces start from 1
SELECT '{1,2,3}'::int[][2:3]; -- result: {2,3}
UPDATE my_array SET my_array [4] = 15000;
UPDATE my_array SET my_array[1:2] = ‘{1,2}’;
SELECT ‘{1,2}’::int[] || ‘{3,4}’::int[]; -- result: {1,2,3,4}
SELECT ARRAY[1,4,3] @> ARRAY[3,1]; -- true
SELECT unnest(string_to_array(‘a.b’, ‘.’));
--- arrays from query
SELECT ARRAY (SELECT * FROM orders WHERE status = ‘pending’);
unnest
text
a
b

6. Data types: Composite
SQL
CREATE TYPE complex AS (
r double precision,
i double precision
);
CREATE TABLE tbl (
cplx complex
);
INSERT INTO tbl VALUES (ROW(1.3, 5.7));
SELECT (cplx).r FROM tbl WHERE (cplx).i > 5.1;
SELECT cplx.r FROM tbl WHERE cplx.i > 5.1; -- Invalid!
UPDATE tbl SET cplx.r = (cplx).r + 1 WHERE ...; -- though SET part doesn’t need parentheses
-- Every table = Composite type
SELECT (tbl) FROM tbl;
tbl
tbl
"("(1.3,5.7)")"

7. Data types: Range
Types
CREATE TABLE reservation (room integer, during tsrange);
INSERT INTO reservation VALUES (1108, '[2010-01-01 14:30, 2010-01-01 15:30)');
SELECT int4range(10, 20) @> 3; -- Containment: false
SELECT numrange(11.1, 22.2) && numrange(20.0, 30.0); -- Overlaps: true (@see EXCLUDE)
SELECT upper(int8range(15, 25)); -- Extract the upper bound: 25
SELECT int4range(10, 20) * int4range(15, 25); -- Compute the intersection: "[15,20)"
SELECT isempty(numrange(1, 5)); -- Is the range empty?: false
Name Description
int4range Range of integer
int8range Range of bigint
numrange Range of numeric
tsrange Range of timestamp without time zone
tstzrange Range of timestamp with time zone
daterange Range of date
SQL

8. Data types: Pseudo
Types
Name Description
any Indicates that a function accepts any input data type.
anyelement Indicates that a function accepts any data type.
anyarray Indicates that a function accepts any array data type.
anynonarray Indicates that a function accepts any non-array data type.
anyenum Indicates that a function accepts any enum data type.
anyrange Indicates that a function accepts any range data type.
cstring Indicates that a function accepts or returns a null-terminated C string.
internal Indicates that a function accepts or returns a server-internal data type.
language_handler A procedural language call handler is declared to return language_handler.
fdw_handler A foreign-data wrapper handler is declared to return fdw_handler.
record dentifies a function returning an unspecified row type.
trigger A trigger function is declared to return trigger.
void Indicates that a function returns no value.
opaque An obsolete type name that formerly served all the above purposes.
SQL
CREATE FUNCTION twice (me anyelement) RETURNS anyelement AS $$
BEGIN
RETURN me * 2;
END; $$ LANGUAGE plpgsql IMMUTABLE;
SELECT twice(2); -- returns: 2::integer

9. Data types: Object Identifier
Types
Name References Description Value example
oid any numeric object identifier 471367
regproc pg_proc function name sum
regprocedure pg_proc function name with argument types sum(integer)
regoper pg_operator operator name +
regoperator pg_operator operator with argument types *(integer,integer) or – (NONE,integer)
regclass pg_class relation name tbl_order
regtype pg_type data type name integer
regconfig pg_ts_config text search configuration english
regdictionary pg_ts_dict text search dictionary simple
SQL
CREATE OR REPLACE FUNCTION test_func(el anyelement, proc regproc)
RETURNS anyelement
AS $$
BEGIN
EXECUTE 'SELECT ' || proc || '(' || el || ')' INTO el; -- don’t repeat it at home! 
RETURN el;
END;
$$ LANGUAGE plpgsql;
SELECT test_func(2, 'twice'::regproc); -- returns: 4

10. Data types: hstore
SQL
CREATE EXTENSION hstore;
SELECT 'a=>1,b=>2'::hstore; SELECT 'a=>1,b=>2'::hstore->'a'; -- key lookup
SELECT hstore(ROW(1, 2)); -- "f1"=>"1", "f2"=>"2"
UPDATE tbl SET h = h || ('c' => '3'); -- merge hstores
UPDATE tbl SET h = delete(h, 'c'); -- delete a key
SELECT * FROM each('a=>1,b=>2');
CREATE TABLE test (col1 integer, col2 text, col3 text);
SELECT * FROM populate_record(null::test, '"col1"=>"456", "col2"=>"zzz"');
key
text
value
text
a 1
b 2
hstore
hstore
"a"=>"1", "b"=>"2"
?column?
text
1
col1
integer
col2
text
col3
text
456 zzz

11. Data types: XML
SQL
XMLPARSE ( { DOCUMENT | CONTENT } value)
-- Examples (ANSI SQL)
XMLPARSE (DOCUMENT '<?xml version="1.0"?><book><title>Manual</title></book>')
XMLPARSE (CONTENT '<title>Manual</title>')
xml '<foo>bar</foo><foo>bar</foo>':: xml -- PostgreSQL Sugar
-- Serialize
XMLSERIALIZE ( { DOCUMENT | CONTENT } value AS type)
-- Generate
SELECT xmlelement(name foo, xmlattribues('xyz' AS bar));
SELECT xpath('/a/text()', '<a href="http://example.com">test</a>');
-- Convert tables/queries to XML
table_to_xml (tbl regclass, nulls boolean, tableforest boolean, targetns text)
query_to_xml(query text, nulls boolean, tableforest boolean, targetns text)
xmlelement
xml
<foo bar=“xyz”/>
xpath
xml[]
{test}

12. Data types: JSON
JSONoperators
SELECT array_to_json('{{1,5},{99,100}}'::int[]); -- [ [1,5],[99,100] ]
SELECT row_to_json(ROW(1, ‘foo’)); -- {"f1":1,"f2":"foo"}
SELECT * FROM json_each('{"a":"foo", "b":"bar"}');
-- hstore -> json
SELECT hstore_to_json(‘”a”=>”foo”,”b”=>”bar”’::hstore);
key
text
value
json
a “foo”
b “bar”
Operator
Right operand
type
Description Example Result
-> int Get JSON array element ‘[1,2,3]’::json->2 3::json
-> text Get JSON object field ‘{“a”:1,”b”:2}’::json->’b’ 2::json
->> int Get JSON array element as text '[1,2,3]'::json->>2 3::text
->> text Get JSON object field as text ‘{“a”:1,”b”:2}’::json->>’b’ 2::text
#> array of text Get JSON object at specified path '{"a":[1,2,3],"b":[4,5,6]}'::json#>'{a,2}' 3::json
#>> array of text Get JSON object at specified path as text '{"a":[1,2,3],"b":[4,5,6]}'::json#>'{a,2}' 3::text
SQL
hstore_to_json
json
{"a":"foo", "b":"bar"}

13. Sequences
SQL
CREATE TABLE tablename ( colname bigserial );
-- is equivalent to:
CREATE SEQUENCE tablename_colname_seq;
CREATE TABLE tablename (
id bigint NOT NULL DEFAULT nextval('tablename_colname_seq')
);
ALTER SEQUENCE tablename_colname_seq OWNED BY tablename.colname;
CREATE [TEMPORARY] SEQUENCE tablename_colname_seq
INCREMENT 1 MINVALUE 1 MAXVALUE 9223372036854775807 START 2
CACHE 1 [CYCLE | NO CYCLE];
Function
Return
type
Description
currval(regclass) bigint Return value most recently obtained with nextval for specified sequence
lastval() bigint Return value most recently obtained with nextval for any sequence
nextval(regclass) bigint Advance sequence and return new value
setval(regclass, bigint) bigint Set sequence's current value
setval(regclass, bigint, boolean) bigint Set sequence's current value and is_called flag
Functions
Important: Because sequences are non-transactional, changes made
by setval are not undone if the transaction rolls back.

14. Tablespaces
SQL
CREATE TABLESPACE fastspace LOCATION '/mnt/sda1/postgresql/data';
CREATE TABLE foo(i int) TABLESPACE fastspace;
SET default_tablespace = another_space;
CREATE TABLE foo(i int); -- created using another_space
SELECT spcname FROM pg_tablespace;
spcname
name
pg_default
pg_global

15. Tables: DDL
SQL
CREATE [ { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXISTS ] table_name ( [
{ column_name data_type [ COLLATE collation ] [ column_constraint [ ... ] ]
| table_constraint
| LIKE source_table [ like_option ... ] }
[, ... ]
] )
[ INHERITS ( parent_table [, ... ] ) ]
[ WITH ( storage_parameter [= value] [, ... ] ) | WITH OIDS | WITHOUT OIDS ]
[ ON COMMIT { PRESERVE ROWS | DELETE ROWS | DROP } ]
[ TABLESPACE tablespace_name ]
--- Examples:
CREATE UNLOGGED TABLE tbl_logs ( event text ); -- no write-ahead logging;
CREATE TEMP TABLE cache ( key text, val text ) ON COMMIT DROP; -- temp, drops on tx
-- From type:
CREATE TYPE employee_type AS (name text, salary numeric);
CREATE TABLE employees OF employee_type (
PRIMARY KEY (name),
salary WITH OPTIONS DEFAULT 1000 -- alters salary column
);

16. Constraints & Domains
SQL
CREATE TABLE IF NOT EXISTS tbl_with_constraints (
id bigserial PRIMARY KEY NOT NULL, -- primary key and not null
-- Unique:
name text UNIQUE NOT NULL,
-- Column check:
items bigint NOT NULL CHECK (items > 0),
-- Foreign key:
user_id bigint NOT NULL
REFERENCES users(id) MATCH SIMPLE -- or FULL
ON UPDATE CASCADE ON DELETE RESTRICT,
-- Table check:
CONSTRAINT con1 CHECK (name <> '' AND items < 1000),
-- Exclusion:
reservation tsrange, EXCLUDE USING gist (c WITH &&)
);
-- Domains:
CREATE DOMAIN dmn_order_sku AS TEXT CHECK (VALUE ~ '^MS-d{1,10}$');
CREATE TABLE tbl_orders (
id SERIAL PRIMARY KEY,
sku dmn_order_sku NOT NULL -- Domain constraint
);

17. Table inheritance (partitioning)
SQL
CREATE TABLE tbl_base_event ( -- base table
id bigserial NOT NULL,
namespace text NOT NULL,
link_id bigint NOT NULL,
message text NOT NULL
);
CREATE TABLE tbl_order_event ( -- child table
CONSTRAINT pk_ohe PRIMARY KEY (id),
CONSTRAINT fk_ohe_order_id FOREIGN KEY (link_id)
REFERENCES tbl_order (id) MATCH SIMPLE
ON UPDATE CASCADE ON DELETE RESTRICT,
CONSTRAINT chk_ohe_namespace CHECK (namespace::text = 'order'::text)
)
INHERITS (tbl_base_event);
INSERT INTO tbl_order_event VALUES (1, 'order', 452, 'created');
SELECT * FROM tbl_base_event; -- OR -- SELECT * FROM tbl_order_event;
SELECT * FROM tbl_base_event ONLY; -- returns empty set
id
bigint
namespace
text
link_id
bigint
message
text
1 order 452 created

18. Indexes
Engines
-- Operator class:
CREATE INDEX idx_bt_my_table_description_varchar_pattern ON my_table
USING btree (description varchar_pattern_ops); -- now you can scan with LIKE using index
-- Functional indexes:
CREATE INDEX idx_featnames_ufullname_varops ON featnames_short
USING btree (upper(fullname) varchar_pattern_ops);
-- Partial indexes:
CREATE TABLE allsubscribers (
id serial PRIMARY KEY, user_name varchar(50) NOT NULL, deactivate timestamptz
);
-- Unique names only for active users
CREATE UNIQUE INDEX uqidx_1 ON allsubscribers
USING btree (lower(user_name)) WHERE deactivate IS NULL;
Name Description
B-tree general purpose, PK & UNIQUE => only b-tree
GiST Generalized Search Tree, full text search, spatial data, astronomical data, hierarchical data + exclusion constraints
GIN Generalized Inverted Index, full text search, trigram extensions,
SP-GiST Space-Partitioning Trees Generalized Search Tree, faster GiST for certain types, support for geometric types
extensions btree_gist, btree_gin, etc.
SQL

19. Window functions: Intro
SELECT id, cost, delivery,
AVG(cost) OVER (PARTITION BY delivery) AS delivery_avg -- agg as window function
FROM tbl_order WHERE date = DATE(CURRENT_TIMESTAMP); -- no GROUP BY clause
SQL
id
bigint
cost
numeric
delivery
text
delivery_avg
numeric
4516 2346.50 b2cpl 4589.23
4576 8300.00 dhl 6392.23
Function Return Type Description
row_number() bigint number of the current row within its partition, counting from 1
rank() bigint rank of the current row with gaps; same as row_number of its first peer
dense_rank() bigint rank of the current row without gaps; this function counts peer groups
percent_rank() double
precision
relative rank of the current row: (rank - 1) / (total rows - 1)
cume_dist() double
precision
relative rank of the current row: (number of rows preceding or peer with current row) / (total rows)
ntile(num_buckets) integer integer ranging from 1 to the argument value, dividing the partition as equally as possible
lag(value any [, offset
integer [, default any ]])
type of value returns value evaluated at the row that is offset rows before the current row within the partition; if
there is no such row, instead return default. Both offset and default are evaluated with respect to the
current row. If omitted, offset defaults to 1 and default to null
lead(value any [, offset
integer [, default any ]])
type of value vice versa
first_value(value any) type of value returns value evaluated at the row that is the first row of the window frame
last_value(value any) type of value returns value evaluated at the row that is the last row of the window frame
nth_value(value any,
nth integer)
type of value returns value evaluated at the row that is the nth row of the window frame (counting from 1); null if
no such row
Anyagg+functions

20. Window functions: Example
-- Given we have a table:
CREATE TABLE tbl_user (id serial, name text, role text);
-- And we perform a query:
SELECT id,
lag(name) OVER w AS prev_user, -- window function over frame
name AS "curr_user",
lead(name) OVER w AS next_user, "role",
COUNT(*) OVER (PARTITION BY "role") AS users_in_role, -- agg over frame
rank() OVER (PARTITION BY "role" ORDER BY id ASC) AS rank_in_role,
FROM tbl_user
WINDOW w AS (ORDER BY id ASC) -- w is a window frame alias
ORDER BY id;
-- Given table: -- Query result:
SQL
id
int
name
text
role
text
1 alice admin
2 bob user
3 john admin
4 sam user
5 ole user
6 ann user
id
int
prev_user
text
curr_user
text
next_user
text
role
text
users_in_role
int
rank_in_role
int
1 alice bob admin 2 1
2 alice bob john user 4 1
3 bob john samn admin 2 2
4 john sam ole user 4 2
5 sam ole ann user 4 3
6 ole ann user 4 4

21. Common Table Expressions
-- Standart CTE:
WITH users_in_role AS (
SELECT "role", COUNT(*) AS total_users FROM tbl_user GROUP BY "role“
)
SELECT id, email, "role", total_users FROM tbl_user
INNER JOIN users_in_role USING ("role");
-- Writeable CTE:
t1 AS (DELETE FROM ONLY logs_2011
WHERE log_ts < '2011-03-01' RETURNING *)
INSERT INTO logs_2011_01_02 SELECT * FROM t1;
SQL
id
int
name
text
role
text
total_users
int
1 alice admin 2
2 bob user 4
3 john admin 2
4 sam user 4
5 ole user 4
6 ann user 4

22. CTE: Upsert
-- Given we have a table
CREATE TABLE tbl ( delivery text, key text, val text, UNIQUE(delivery, key) );
-- Upsert:
LOCK TABLE tbl IN SHARE ROW EXCLUSIVE MODE;
WITH new_values ( "delivery", "key", "val" ) AS ( -- dynamic type definition
VALUES ('dhl', 'url', 'dhl.com') -- dynamic rows definition
),
upsert AS (
UPDATE tbl m SET "val" = nv."val"
FROM new_values nv
WHERE (m."delivery", m."key") = (nv."delivery", nv."key") -- row comparison
RETURNING m.* -- writeable CTE
)
INSERT INTO tbl ("delivery", "key", "val")
SELECT "delivery", "key", "value"
FROM new_values
WHERE NOT EXISTS (
SELECT 1
FROM upsert AS up
WHERE (up."delivery", up."key") = (new_values."delivery", new_values."key")
);
SQL

23. CTE: Recursive
WITH RECURSIVE t(n) AS (
-- initial part:
VALUES (1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
UNION ALL
-- recursive part:
SELECT n+1, (n+1)*2, (n+1)*3, (n+1)*4, (n+1)*5, (n+1)*6, (n+1)*7, (n+1)*8, (n+1)*9, (n+1)*10
FROM t WHERE n < 10
)
SELECT * FROM t;
SQL
n
int
column2
int
column3
int
column4
int
column5
int
column6
int
column7
int
column8
int
column9
int
column10
int
1 2 3 4 5 6 7 8 9 10
2 4 6 8 10 12 14 16 18 20
3 6 9 12 15 18 21 24 27 30
4 8 12 16 20 24 28 32 36 40
5 10 15 20 25 30 35 40 45 50
6 12 18 24 30 36 42 48 54 60
7 14 21 28 35 42 49 56 63 70
8 16 24 32 40 48 56 64 72 80
9 18 27 36 45 54 63 72 81 90
10 20 30 40 50 60 70 80 90 100

24. CTE: Recursive (Adjacency List)
CREATE TABLE tree (id serial, name text, parent_id int); -- given we have a table
-- And we query:
WITH RECURSIVE tree_rec AS (
SELECT id, name, parent_id, '' AS path, '+' AS x, '' AS mp FROM tree WHERE parent_id IS NULL
UNION ALL
SELECT tree_iter.id, tree_iter.name, tree_iter.parent_id, (tree_rec.path || '| ') AS path, (path || '|--
+ ' || tree_iter.name) AS x,
(tree_rec.mp || '/' || tree_iter.parent_id || '.' || tree_iter.id) AS mp
FROM tree AS tree_iter
INNER JOIN tree_rec ON tree_iter.parent_id = tree_rec.id -- recursive join!
)
SELECT repeat(' ', strpos(x, '|') - 1) || substring(x FROM strpos(x, '|')) FROM tree_rec
ORDER BY mp;
-- Given table: -- Query result:
SQL
id
int
name
text
parent_id
int
1 root NULL
2 a 1
3 ab 2
4 b 1
5 bc 4
6 bcd 5
?column?
text
+
|--+ a
| |--+ ab
|--+ b
| |--+ bc
| | |--+ bcd

25. Functions: Intro
-- SQL:
CREATE OR REPLACE FUNCTION add(integer, integer) RETURNS integer
AS 'select $1 + $2;'
LANGUAGE SQL
IMMUTABLE -- IMMUTABLE |VOLATILE | STABLE
STRICT; -- STRICT | CALLED ON NULL INPUT
-- PL/PGSQL:
CREATE FUNCTION concat_lower_or_upper(a text, b text, uppercase boolean DEFAULT false)
RETURNS text AS $$
RETURN CASE
WHEN uppercase THEN upper(a || ' ' || b)
ELSE lower(a || ' ' || b)
END;
$$ LANGUAGE plgpsql IMMUTABLE STRICT;
-- Invocations:
SELECT concat_lower_or_upper('Hello', 'World', true); -- positional args
SELECT concat_lower_or_upper(a := 'Hello', b := 'World'); -- named args
SELECT concat_lower_or_upper(a := 'Hello', uppercase := true, b := 'World'); -- named args
SELECT concat_lower_or_upper('Hello', 'World', uppercase := true); -- mixed
SQL

26. Functions: Example
CREATE OR REPLACE FUNCTION order_txs(i_order_id bigint)
RETURNS hstore
AS $$
DECLARE h hstore;
DECLARE r RECORD;
BEGIN
h = hstore(ARRAY[]::text[]); -- empty hstore
FOR r IN SELECT "type", SUM(amount) AS amount FROM tbl_txs WHERE order_id = i_order_id GROUP BY "type" LOOP
h = h || hstore(r.type, r.amount::text);
END LOOP;
RETURN h;
$$
LANGUAGE plgsql VOLATILE;
-- Example:
SELECT id, order_txs(id) AS txs FROM tbl_order WHERE id IN (21356, 46724);
SQL
id
bigint
txs
hstore
21356 "ds_pfr" => "2748.56", "pay_cost" => "2748.56"
46724 "service_sms" => "6.00"

27. Functions: DO
DO $$
DECLARE r RECORD;
DECLARE txs hstore;
DECLARE s numeric;
BEGIN
FOR r IN SELECT id FROM tbl_order LOOP
txs = order_txs(r.id);
s = txs->'ds_pfr'::numeric + txs->'ds_cost'::numeric;
RAISE NOTICE 'Order % -> %', r.id, s;
UPDATE tbl_order SET debts = s WHERE id = r.id;
END LOOP;
END;
$$
LANGUAGE plgsql;
-- Output:
-- Order 24677 -> 346.56
-- Order 5677 -> 289.45
-- …
SQL

28. Functions: JavaScript
CREATE EXTENSION plv8; -- we need an extension
-- Define a function:
CREATE FUNCTION plv8_test(keys text[], vals text[]) RETURNS text AS $$
var o = {};
for(var i=0; i<keys.length; i++){
o[keys[i]] = vals[i];
}
return JSON.stringify(o);
$$ LANGUAGE plv8 IMMUTABLE STRICT;
-- Invoke it:
SELECT plv8_test(ARRAY['name', 'age'], ARRAY['Tom', '29']);
SQL
?column?
text
{"name":"Tom","age":"29"}

29. Functions: Triggers
-- Given we have an orders table:
CREATE TABLE tbl_order (id bigserial, …);
-- And a log table:
CREATE TABLE tbl_order_history_event ( order_id bigint, data json );
-- And we want to log insertions/updates on each particular order:
CREATE FUNCTION log_order_event() RETURNS trigger AS $$
BEGIN
INSERT INTO tbl_order_history_event
VALUES (NEW.id, to_json(data));
RETURN NEW;
END; $$ LANGUAGE plpgsql;
-- Trigger:
CREATE TRIGGER trigger_log_order_event -- trigger name
AFTER -- BEFORE | INSTEAD OF | AFTER
INSERT OR UPDATE ON tbl_order -- INSERT|UPDATE|DELETE
FOR EACH ROW – ROW|STATEMENT
EXECUTE PROCEDURE log_order_event();
SQL

30. Custom operators
-- Define operator function:
CREATE OR REPLACE FUNCTION fn_order_has_tx(i_order_id bigint, i_tx_type text)
RETURNS boolean AS $$
BEGIN
RETURN EXISTS (
SELECT 1 FROM tbl_order_money_transaction
WHERE order_id = i_order_id AND "type" = i_tx_type
);
END;
$$ LANGUAGE plpgsql;
-- Define operator:
CREATE OPERATOR @? (
LEFTARG = bigint,
RIGHTARG = text,
PROCEDURE = fn_order_has_tx
);
-- Use it:
SELECT COUNT(*) FROM tbl_order WHERE id @? 'ds_payment_from_recipient';
SQL
COUNT(*)
int
42185

31. Custom aggregates
-- Define state function:
CREATE OR REPLACE FUNCTION geom_mean_state(prev numeric[2], next numeric)
RETURNS numeric[2] AS $$
SELECT CASE WHEN $2 IS NULL OR $2 = 0 THEN $1
ELSE ARRAY[coalesce($1[1],0) + ln($2), $1[2] + 1] END;
$$ LANGUAGE sql IMMUTABLE;
-- Define final function:
CREATE OR REPLACE FUNCTION geom_mean_final(numeric[2])
RETURNS numeric AS $$
SELECT CASE WHEN $1[2] > 0 THEN exp($1[1]/$1[2]) ELSE 0 END;
$$ LANGUAGE sql IMMUTABLE;
-- Create aggregate:
CREATE AGGREGATE geom_mean(numeric) (
SFUNC=geom_mean_state, STYPE=numeric[],
FINALFUNC=geom_mean_final, INITCOND='{0,0}');
-- Use it:
SELECT geom_mean(val) FROM ( VALUES(2), (5), (3) ) AS t (val);
SQL
?column?
numeric
3.10723250595385889234

32. Foreign Data Wrappers
Types
SQL
postgres_fdw
oracle_fdw
mysql_fdw
odbc_fdw
jdbc_fdw
informix_fdw
firebird_fdw
sqlite_fdw
tds_fdw
NoSQL
couchdb_fdw
MonetDB_fdw
mongo_fdw
redis_fdw
Neo4j fdw
Tycoon fdw
File
file_fdw
file_text_array_fdw
file_fixed_length_record_fdw
json_fdw
Other
twitter_fdw
ldap_fdw
PGStorm
Hadoop fdw
s3_fdw
www_fdw
cstore_fdw

33. FDW: File example
CREATE EXTENSION file_textarray_fdw; -- install extension if needed
CREATE SERVER file_tafdw_server FOREIGN DATA WRAPPER file_textarray_fdw;
-- User mapping (not always necessary):
CREATE USER MAPPING FOR public SERVER file_tafdw_server;
CREATE FOREIGN TABLE fgn_tbl_delivery( x text[] ) SERVER file_tafdw_server
OPTIONS (filename '/data.csv', encoding 'utf8', delimiter ':');
--Query:
SELECT x[1] AS delivery, x[2] AS origin_id FROM fgn_tbl_delivery
WHERE x[2]::int < 1000;
SQL
Given we have a file /data.csv with following contents:
axiomus:4
dhl:10
b2cpl:3967
delivery
text
origin_id
text
axiomus 4
dhl 10

34. Materialized Views
-- Create materialized view from query;
CREATE MATERIALIZED VIEW vw_orders_with_txs AS
SELECT *, order_txs(id) AS order_txs FROM tbl_order;
SELECT * FROM vw_orders_with_txs WHERE order_txs->'ds_pfr'::numeric > 1000;
-- Though you have to refresh it manually:
REFRESH MATERIALIZED VIEW vw_orders_with_txs;
-- Create materialized view from foreign table:
CREATE EXTENSION file_fdw;
CREATE SERVER local_file FOREIGN DATA WRAPPER file_fdw;
CREATE FOREIGN TABLE words (word text NOT NULL)
SERVER local_file
OPTIONS (filename '/etc/dictionaries-common/words');
CREATE MATERIALIZED VIEW vw_words AS SELECT * FROM words;
CREATE UNIQUE INDEX wrd_word ON vw_words (word);
CREATE EXTENSION pg_trgm;
CREATE INDEX wrd_trgm ON vw_words USING gist (word gist_trgm_ops);
VACUUM ANALYZE vw_words;
SELECT COUNT(*) FROM vw_words WHERE word = 'caterpiler';
SQL

35. Misc: COPY PROGRAM
-- Copy TO external program:
COPY (SELECT 1, 2) TO PROGRAM 'sed -e "s/,/:/" > ~/test.txt' DELIMITER ',';
-- COPY FROM external program:
CREATE TABLE weather_json (cities json);
COPY weather_json FROM PROGRAM 'curl
http://api.openweathermap.org/data/2.5/weather?q=Tokyo';
SELECT cities->'name' FROM weather_json;
SQL
$ cat ~/test.txt
1:2
?column?
text
"Tokyo"

36. Postgres-specific features
-- Shorthand casting using ::
SELECT '1.2'::numeric; /* SAME AS */ SELECT CAST('1.2' AS numeric);
-- DISTINCT ON
SELECT DISTINCT ON (left(origin_id, 5)) id, name, left(origin_id, 5)
FROM tbl_order WHERE delivery = 'dhl';
-- Case insensitive LIKE
SELECT * FROM tbl_order WHERE delivery ILIKE '%hl';
-- Set Returning Functions in SELECT -- Complex types in queries:
SELECT n, generate_series(1, n) SELECT tree FROM tree LIMIT 4;
FROM ( VALUES(1), (2) ) AS tbl (n);
-- RETURNING changed records:
UPDATE tbl_order SET status = 'error' WHERE status = 'unknown'
RETURNING id; -- returns set of records
SQL
id
int
generate_series
n
1 1
2 1
2 2
tree
tree
(1,root,)
(2,a,1)
(3,ab,2)
(4,b,1)

37. Resources
Resources
Name Url
Documentation http://www.postgresql.org/docs/9.3/interactive/index.html
Postgresql wiki http://wiki.postgresql.org/wiki/Main_Page
Posgresql online journal http://www.postgresonline.com
Books
Title
PostgreSQL: Up and Running
PostgreSQL: Introduction And Concepts

38. THE
END
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