Postgre sql statements 03

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PostgreSQL Statements

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MEMBERS
● Huy Phan-Dang
● Phuc Nguyen-Dang-Hong
● Vu Nguyen-Dinh-Hoang
● Le Huynh
● Duy Nguyen-Van

CONTENTS
● Functions
● Views
● Triggers
● Indexes

PostgreSQL Statements 3

CONTENTS
● Functions
● Views
● Triggers
● Indexes


FUNCTIONS (1/18)
● What is a Function?
 A Function is a set of sql statements which aim to
accomplish the same task.
 How is a function different from a procedure?
✔ A Function is more clear, organized and structured.
✔ It is easy to modify.
✔ It is easy to handle return values than in procedures. In
procedures, a temporary table might be necessary to carry
a return value and join it with an existing table. This
becomes unnecessary if functions are used instead.


FUNCTIONS (2/18)
● CREATE FUNCTION - define a new function.
● DROP FUNCTION - remove a function.
● ALTER FUNCTION - change the definition of a
function.


FUNCTIONS (3/18)
● CREATE FUNCTION - define a new function.
● Synopsis
CREATE FUNCTION name ( [ [ argmode ]
[ argname ] argtype [, …] ] )
RETURNS returntype
AS 'definition'
LANGUAGE 'langname'
● Create or Replace Function will either create a
new function, or replace an existing definition.


FUNCTIONS (4/18)
● CREATE FUNCTION
 Parameters
✔ Name: The name (optionally schema-qualified) of the
function to create.
✔ Argmode: The mode of an argument: either IN, OUT, or
INOUT. If omitted, the default is IN.
✔ Argname: The name of an argument.
✔ Argtype: The data type(s) of the function's arguments
(optionally schema-qualified), if any.
✔ Returntype: The return data type (optionally schema-
qualified).


FUNCTIONS (5/18)
● CREATE FUNCTION
 Parameters
✔ Langname: The name of the language that the function is
implemented in. May be SQL, C, internal, or the name of a
user-defined procedural language. For backward
compatibility, the name may be enclosed by single quotes.
✔ Definition: A string constant defining the function; the
meaning depends on the language. It may be an internal
function name, the path to an object file, an SQL command,
or text in a procedural language.


FUNCTIONS (6/18)
● CREATE FUNCTION
 Notice
✔ The name of the new function must not match any existing
function with the same argument types in the same
schema.
✔ However, functions of different argument types may share a
name (this is called overloading).


FUNCTIONS (7/18)
● CREATE FUNCTION
 Notice
✔ To update the definition of an existing function, use
CREATE OR REPLACE FUNCTION. It is not possible to
change the name or argument types of a function this way
(if you tried, you would actually be creating a new, distinct
function).
✔ Also, CREATE OR REPLACE FUNCTION will not let you
change the return type of an existing function. To do that,
you must drop and recreate the function.


FUNCTIONS (8/18)
● CREATE FUNCTION
 Notice
✔ If you drop and then recreate a function, the new function is
not the same entity as the old; you will have to drop existing
rules, views, triggers, etc. that refer to the old function.
✔ Use CREATE OR REPLACE FUNCTION to change a
function definition without breaking objects that refer to the
function.


FUNCTIONS (9/18)
● CREATE FUNCTION
 Example: Suppose we have a SQL statement:
INSERT INTO user VALUES(1,'Huỳnh Lê',21);
INSERT INTO user VALUES(2,'Văn Duy',23);
INSERT INTO user VALUES(3,'Đăng Huy',21);
INSERT INTO user VALUES(4,'Hồng Phúc',21);


FUNCTIONS (10/18)
● CREATE FUNCTION
 Example
✔ Create 1 function with name insert_user
CREATE OR REPLACE FUNCTION insert_user(id integer,
username character, age integer)
RETURNS void AS
$BODY$ BEGIN
INSERT INTO "user" (id,name,age) VALUES
(id,username,age);
END $BODY$
LANGUAGE plpgsql


FUNCTIONS (11/18)
● CREATE FUNCTION
 Example
✔ Use this function
SELECT insert_user(1, 'Huỳnh Lê', 21);
SELECT insert_user(2, 'Văn Duy', 23);
SELECT insert_user(3, 'Đăng Huy', 21);
SELECT insert_user(4, 'Hồng Phúc',21);


FUNCTIONS (12/18)
● DROP FUNCTION - remove a function.
● Synopsis
DROP FUNCTION [ IF EXISTS ] name ( [ [ argmode ] [
argname ] argtype [, ...] ] ) [ CASCADE | RESTRICT ]
● Description
 DROP FUNCTION removes the definition of an
existing function. To execute this command the user
must be the owner of the function. The argument
types to the function must be specified, since several
different functions may exist with the same name
and different argument lists.


FUNCTIONS (13/18)
● DROP FUNCTION
 Parameters
✔ IF EXISTS: Do not throw an error if the function does not
exist. A notice is issued in this case.
✔ Name: The name (optionally schema-qualified) of an
existing function.
✔ Argmode, argname, argtype: function's arguments
✔ CASCADE: Automatically drop objects that depend on the
function (such as operators or triggers).
✔ RESTRICT: Refuse to drop the function if any objects
depend on it. This is the default.


FUNCTIONS (14/18)
● DROP FUNCTION
 Example
✔ This command removes the square root function
DROP FUNCTION sqrt(integer);


FUNCTIONS (15/18)
● ALTER FUNCTION - change the definition of a
function
● Synopsis
 ALTER FUNCTION name ( [ [ argmode ] [ argname ]
argtype [, ...] ] ) action [, ... ] [ RESTRICT ]
argtype [, ...] ] ) RENAME TO new_name
argtype [, ...] ] ) OWNER TO new_owner


FUNCTIONS (16/18)
● ALTER FUNCTION
argtype [, ...] ] ) SET SCHEMA new_schema
 Notice
✔ You must own the function to use ALTER FUNCTION. To
change a function's schema, you must also have CREATE
privilege on the new schema. To alter the owner, you must
also be a direct or indirect member of the new owning role,
and that role must have CREATE privilege on the function's
schema.


FUNCTIONS (17/18)
● ALTER FUNCTION
 Parameters
✔ name: The name (optionally schema-qualified) of an
existing function.
✔ argmode, argname, argtype: function's arguments
✔ new_name: The new name of the function.
✔ new_owner: The new owner of the function. Note that if the
function is marked SECURITY DEFINER, it will
subsequently execute as the new owner.
✔ new_schema: The new schema for the function.


FUNCTIONS (18/18)
● ALTER FUNCTION
 Examples
✔ To rename the function sqrt for type integer to square_root:
ALTER FUNCTION sqrt(integer) RENAME TO square_root;
✔ To change the owner of the function sqrt for type integer to
HuynhLe:
ALTER FUNCTION sqrt(integer) OWNER TO HuynhLe;
✔ To change the schema of the function sqrt for type integer
to maths:
ALTER FUNCTION sqrt(integer) SET SCHEMA maths;


CONTENTS
● Functions
● Views
● Triggers
● Indexes


VIEWS (1/8)
● In SQL, a view is a virtual table based on the
result-set of an SQL statement.
● A view contains rows and columns, just like a
real table. The fields in a view are fields from
one or more real tables in the database.
● You can add SQL functions, WHERE, and JOIN
statements to a view and present the data as if
the data were coming from one single table.


VIEWS (2/8)
● CREATE VIEW Syntax
CREATE [ OR REPLACE ] [ TEMP | TEMPORARY ] VIEW
name [ ( column_name [, ...] ) ] AS query
 CREATE VIEW defines a view of a query. The view is not
physically materialized. Instead, the query is run every time
the view is referenced in a query.
 CREATE OR REPLACE VIEW is similar, but if a view of the
same name already exists, it is replaced. You can only
replace a view with a new query that generates the identical
set of columns (i.e., same column names and data types).


VIEWS (3/8)
● CREATE VIEW
 Parameters
✔ TEMPORARY or TEMP: If specified, the view is created as
a temporary view. Temporary views are automatically
dropped at the end of the current session. Existing
permanent relations with the same name are not visible to
the current session while the temporary view exists, unless
they are referenced with schema-qualified names.
✔ Name: The name (optionally schema-qualified) of a view to
be created.


VIEWS (4/8)
● CREATE VIEW
 Parameters
✔ column_name: An optional list of names to be used for
columns of the view. If not given, the column names are
deduced from the query.
✔ Query: A query (that is, a SELECT statement) which will
provide the columns and rows of the view.


VIEWS (5/8)
● CREATE VIEW
 Examples: Create a view consisting of all comedy
films:
CREATE VIEW comedies AS
SELECT *
FROM films
WHERE kind = 'Comedy';
 To use: SELECT * FROM comedies


VIEWS (6/8)
● DROP VIEW — remove a view
● Synopsis
 DROP VIEW name [, ...] [ CASCADE | RESTRICT
✔ DROP VIEW drops an existing view. To execute this
command you must be the owner of the view.


VIEWS (7/8)
● DROP VIEW
 Parameters
✔ Name: The name (optionally schema-qualified) of the view
to remove.
view (such as other views).
✔ RESTRICT: Refuse to drop the view if any objects depend
on it. This is the default.


VIEWS (8/8)
● DROP VIEW
 Examples: This command will remove the view
called kinds:
✔ DROP VIEW kinds;


CONTENTS
● Functions
● Views
● Triggers
● Indexes


TRIGGERS (1/11)
● A trigger is a specification that the database
should automatically execute a particular
function whenever a certain type of operation is
performed. Triggers can be defined to execute
either before or after any INSERT, UPDATE, or
DELETE operation, either once per modified
row, or once per SQL statement.
● If a trigger event occurs, the trigger's function is
called at the appropriate time to handle the
event.


TRIGGERS (2/11)
● The trigger function must be defined before the
trigger itself can be created. The trigger function
must be declared as a function taking no
arguments and returning type trigger.
● Once a suitable trigger function has been
created, the trigger is established with CREATE
TRIGGER. The same trigger function can be
used for multiple triggers.


TRIGGERS (3/11)
● CREATE TRIGGER
CREATE TRIGGER name { BEFORE | AFTER }
{ event [ OR ... ] }
ON table [ FOR [ EACH ] { ROW | STATEMENT } ]
EXECUTE PROCEDURE funcname ( arguments )


TRIGGERS (4/11)
● CREATE TRIGGER
 Parameters
✔ Name: The name to give the new trigger. This must be
distinct from the name of any other trigger for the same
table.
✔ Before/After: Determines whether the function is called
before or after the event.
✔ Event: One of INSERT, UPDATE, or DELETE; this specifies
the event that will fire the trigger. Multiple events can be
specified using OR.
✔ Table: The name (optionally schema-qualified) of the table
the trigger is for.


TRIGGERS (5/11)
● CREATE TRIGGER
 Parameters
✔ For each row / for each statement: This specifies whether
the trigger procedure should be fired once for every row
affected by the trigger event, or just once per SQL
statement. If neither is specified, for each statement is the
default.
✔ Funcname: A user-supplied function that is declared as
taking no arguments and returning type trigger, which is
executed when the trigger fires.


TRIGGERS (6/11)
● CREATE TRIGGER
 Example
CREATE TABLE emp (
empname text,
salary integer,
last_date timestamp,
last_user text
);


TRIGGERS (7/11)
● CREATE TRIGGER
 Example
CREATE FUNCTION emp_stamp() RETURNS trigger AS
$emp_stamp$
BEGIN
IF NEW.empname IS NULL THEN
RAISE EXCEPTION 'Nhap ten nhan vien';
END IF;
IF NEW.salary IS NULL THEN
RAISE EXCEPTION 'Nhap tien luong', NEW.empname;
END IF;


TRIGGERS (8/11)
● CREATE TRIGGER
 Example
NEW.last_date := current_timestamp;
NEW.last_user := current_user;
RETURN NEW;
END;
$emp_stamp$ LANGUAGE plpgsql;

CREATE TRIGGER emp_stamp BEFORE INSERT OR
UPDATE ON emp
FOR EACH ROW EXECUTE PROCEDURE emp_stamp();


TRIGGERS (9/11)
● Several special variables
 NEW: Data type RECORD; variable holding the new
database row for INSERT/UPDATE operations in
row-level triggers. This variable is NULL in
statement-level triggers.
 OLD: Data type RECORD; variable holding the old
database row for UPDATE/DELETE operations in
row-level triggers. This variable is NULL in
statement-level triggers.


TRIGGERS (10/11)
 TG_NAME: Data type name; variable that contains
the name of the trigger actually fired.
 TG_WHEN: Data type text; a string of either
BEFORE or AFTER depending on the trigger's
definition.
 TG_LEVEL: Data type text; a string of either ROW or
STATEMENT depending on the trigger's definition.
 TG_OP: Data type text; a string of INSERT,
UPDATE, or DELETE telling for which operation the
trigger was fired.


TRIGGERS (11/11)
 TG_RELID: Data type oid; the object ID of the table
that caused the trigger invocation.
 TG_RELNAME: Data type name; the name of the
table that caused the trigger invocation.
 TG_NARGS: Data type integer; the number of
arguments given to the trigger procedure in the
CREATE TRIGGER statement.
 TG_ARGV[]: Data type array of text; the arguments
from the CREATE TRIGGER statement. The index
counts from 0. Invalid indices (less than 0 or greater
than or equal to tg_nargs) result in a null value.


CONTENTS
● Functions
● Views
● Triggers
● Indexes


INDEXES (1/12)
● An index can be created in a table to find data
more quickly and efficiently.
● The users cannot see the indexes, they are just
used to speed up searches/queries.
● Note: Updating a table with indexes takes more
time than updating a table without (because the
indexes also need an update). So you should
only create indexes on columns (and tables)
that will be frequently searched against.


INDEXES (2/12)
● CREATE INDEX Syntax
CREATE [ UNIQUE ] INDEX name ON table
[ USING method ] ( { column | ( expression ) }
[ opclass ] [, ...] )
[ TABLESPACE tablespace ]
[ WHERE predicate ]


INDEXES (3/12)
● CREATE INDEX
 Parameters
✔ UNIQUE: Causes the system to check for duplicate values
in the table when the index is created (if data already exist)
and each time data is added. Attempts to insert or update
data which would result in duplicate entries will generate an
error.
✔ Name: The name of the index to be created. No schema
name can be included here; the index is always created in
the same schema as its parent table.
✔ Table: The name (possibly schema-qualified) of the table to
be indexed.


INDEXES (4/12)
● CREATE INDEX
 Parameters
✔ Method: The name of the method to be used for the index.
Choices are btree, hash, rtree, and gist. The default
method is btree.
✔ Column: The name of a column of the table.
✔ Expression: An expression based on one or more columns
of the table. The expression usually must be written with
surrounding parentheses, as shown in the syntax.
However, the parentheses may be omitted if the expression
has the form of a function call.


INDEXES (5/12)
● CREATE INDEX
 Parameters
✔ Opclass: The name of an operator class. See below for
details.
✔ Tablespace: The tablespace in which to create the index.
✔ Predicate: The constraint expression for a partial index.


INDEXES (6/12)
● CREATE INDEX
 Example: The following command can be used to
create an index on the id column, as discussed:
✔ CREATE INDEX test1_id_index ON test1 (id);


INDEXES (7/12)
● CREATE INDEX
 Notice: An index can be defined on more than one
column of a table.
✔ CREATE INDEX test2_mm_idx ON test2 (major, minor);


INDEXES (8/12)
● DROP INDEX Syntax
 DROP INDEX drops an existing index from the
database system. To execute this command you
must be the owner of the index.
✔ DROP INDEX name [, ...] [ CASCADE | RESTRICT ]
 Parameters
✔ Name: The name (optionally schema-qualified) of an index
to remove.
index.
✔ RESTRICT: Refuse to drop the index if any objects depend
on it. This is the default.


INDEXES (9/12)
● DROP INDEX
 Example: This command will remove the index
title_idx:
✔ DROP INDEX title_idx;


INDEXES (10/12)
● ALTER INDEX Syntax
 ALTER INDEX name RENAME TO new_name
 ALTER INDEX name SET TABLESPACE
tablespace_name
✔ ALTER INDEX changes the definition of an existing index.
✔ RENAME: The RENAME form changes the name of the
index. There is no effect on the stored data.
✔ SET TABLESPACE: This form changes the index's
tablespace to the specified tablespace and moves the data
file(s) associated with the index to the new tablespace


INDEXES (11/12)
● ALTER INDEX
 Parameters
✔ Name: The name (possibly schema-qualified) of an existing
index to alter.
✔ new_name: New name for the index.
✔ tablespace_name: The tablespace to which the index will
be moved.


INDEXES (12/12)
● ALTER INDEX
 Examples:
✔ To rename an existing index:
ALTER INDEX distributors RENAME TO suppliers;
✔ To move an index to a different tablespace:
ALTER INDEX distributors SET TABLESPACE fasttablespace;


Reference
● PostgreSQL 9.1.0 Documentation
● pgadmin.org


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