SQL III SQL III

PseudocolumnsPseudocolumns

Rownum (numeric) A number for each row in a select query Example:

Branch(bname, bcity) SELECT rownum ordered_branch_seq, bname, bcity FROM branch

ORDER BY bname;

Rowid (char string) A character string that represents the physical address for a row of a

table. SELECT rowid, bname, bcity FROM branch.

Access by rowid fastest. However, rowids may change during some table maintenance

operations Split of table partitions. If you delete and insert the same branch name, the rowids for that row

are likely to be different

CONNECT-BY (not in book)CONNECT-BY (not in book)

Person (father, name)

Find the children of ‘Mike Johnson’ SELECT a.name FROM Person a

where a.father = ‘Mike Johnson’;

What-if you want to find great-great-grandchildren?

Easier way in Oracle: CONNECT-BY Useful for answering hierarchical queries

CONNECT-BYCONNECT-BY

Find all descendants from Mike Johnson SELECT a.name FROM Person a

START WITH a.name = ‘Mike Johnson’

CONNECT BY PRIOR name = father;

First Level (of recursion) Mike Johnson

Second Level All names for which Mike is a father (i.e., children of Mike)

Third Level All names for which Mike’s children are fathers

….

CONNECT-BYCONNECT-BY

Find all descendants from Mike Johnson SELECT a.name FROM Person a

START WITH a.name = ‘Mike Johnson’

CONNECT BY PRIOR name = father;

Pseudocolumn: LEVELSELECT a.name, LEVEL FROM Person a

START WITH a.name = ‘Mike Johnson’

CONNECT BY PRIOR name = father;

Ordering among siblings:SELECT a.name, LEVEL FROM Person a

START WITH a.name = ‘Mike Johnson’

CONNECT BY PRIOR name = father

ORDER SIBLINGS BY name;

CONNECT-BYCONNECT-BY

Find upto grand-children only for Mike Johnson Restrict the LEVEL to be <=3 (Mike, his children and grand-children)

What if you have “loops” in the data? Oracle raises an error To ignore the loops, specify NOCYCLE

SELECT a.name, LEVEL FROM Person a

START WITH a.name = ‘Mike Johnson’

CONNECT BY NOCYCLE PRIOR name = father

ORDER SIBLINGS BY name;

Lot more Information: Oracle Help links, or

http://www.oracle.com/technology/oramag/webcolumns/2003/techarticles/gennick_connectby.html

http://www.stanford.edu/dept/itss/docs/oracle/10g/server.101/b10759/queries003.htm

SQL SummarySQL SummaryQuery Language (DML):

SELECT, FROM, WHEREGROUP BY, HAVINGORDER BYNested Queries (IN, EXISTS, UNIQUE, ALL, SOME, correlation)AggregatesJoinsUpdatesViewsPseudoColumnsConnect-by hierarchical queries

More to come: Inserts, deletes ,….DDL:

CREATE TABLEDROP TABLEALTER TABLE

Embedded SQL/JDBCIntegrity ConstraintsSecurity, authorization

SQL: Modification CommandsSQL: Modification Commands

Deletion: DELETE FROM <relation>[WHERE <predicate>]

Example:

1. DELETE FROM account -- deletes all tuples in account

2. DELETE FROM account WHERE bname in (SELECT bname FROM branch WHERE bcity = ‘Bkln’) -- deletes all accounts from Brooklyn branch

DELETEDELETE

Delete the record of all accounts with balances below the average at the bank.

DELETE FROM accountWHERE balance < (SELECT AVG(balance)

FROM account)

Problem: as we delete tuples from deposit, the average balance changes

Solution used in SQL:

1. First, compute avg balance and find all tuples to delete

2. Next, delete all tuples found above (without recomputing avg or retesting the tuples)

SQL: Modification CommandsSQL: Modification CommandsInsertion: INSERT INTO <relation> values (.., .., ...)

or INSERT INTO <relation>(att1, .., attn)

values( ..., ..., ...)

or INSERT INTO <relation> <query expression>

Examples: INSERT INTO account VALUES (“Perry”, A-768, 1200)

or INSERT INTO account( bname, acct_no, balance) VALUES (“Perry”, A-768, 1200)

INSERT INTO account SELECT bname, lno, 200 FROM loan WHERE bname = “Kenmore”

gives free $200 savings account for each loan holder at Kenmore

SQL: Modification CommandsSQL: Modification Commands

Update: UPDATE <relation>

SET <attribute> = <expression>

WHERE <predicate>

Ex. UPDATE account SET balance = balance * 1.06 WHERE balance > 10000

UPDATE account SET balance = balance * 1.05 WHERE balance <= 10000

Alternative: UPDATE account SET balance = (CASE

WHEN balance <= 10000 THEN balance*1.05 ELSE balance*1.06 END)

SQL: Modification CommandsSQL: Modification CommandsView Updates:

Suppose we have a view: CREATE VIEW branch-loan AS SELECT bname, lno FROM loan

And we insert: INSERT INTO branch-loan VALUES( “Perry”, L-308)

Then, the system will insert a new tuple ( “Perry”, L-308, NULL) into loan

SQL: Modification CommandsSQL: Modification CommandsWhat about...

CREATE VIEW depos-account AS SELECT cname, bname, balance FROM depositor as d, account as a WHERE d.acct_no = a.acct_no

INSERT INTO depos-account VALUES( “Smith”, “Perry”, 500)

How many relations we need to update?

Many systems disallow

Built-in Data Types in SQL Built-in Data Types in SQL

date: Dates, containing a (4 digit) year, month and date Example: date ‘2005-7-27’

time: Time of day, in hours, minutes and seconds. Example: time ‘09:00:30’ time ‘09:00:30.75’

timestamp: date plus time of day Example: timestamp ‘2005-7-27 09:00:30.75’

interval: period of time Example: interval ‘1’ day

Subtracting a date/time/timestamp value from another gives an interval value

Interval values can be added to date/time/timestamp values

CREATE TABLE person (name VARCHAR2, age NUMBER);

What other data types other than VARCHAR2, NUMBER are allowed?

Build-in Data Types in SQL (Cont.)Build-in Data Types in SQL (Cont.)

Can extract values of individual fields from date/time/timestamp Example: extract (year from r.starttime)

Can cast string types to date/time/timestamp Example: cast <string-valued-expression> as date

Example: cast <string-valued-expression> as time

Other Built-in Special typesOther Built-in Special types

Special Types XMLType (we will see examples at the end of the course)

SDO_GEOMETRY (spatial type) to store 2-d, 3-d geometries

Media Types ORDImage

ORDAudio

ORDDoc,…

User-Defined TypesUser-Defined Types

create type construct in SQL creates user-defined type

create type Dollars as numeric (12,2) final

Can create user-defined object types Name, attributes Methods (implemeneted in plsql or other external languages) Example

CREATE TYPE geometry as OBJECT ( type varchar2(10),

vertex_ordinates number_array);

REF datatypes Reference to the OID (object identifier) of an object

Other TypesOther Types

VARRAYs Ordered set of elements Each element has an index and can be accessed using that. Example:

CREATE TYPE number_array as VARRAY(100000) of NUMBER;

VARRAY can be: The datatype of a column in a table

CREATE TABLE properties ( name varchar2(32), geom NUMBER_ARRAY);

Attribute of an object PL/SQL variable, parameter, or return type

Query: cast it using the TABLE keyword to a table SELECT * from TABLE( select geom from properties where

name=‘CityHall’));

Nested TablesNested Tables

Nested Table (compared to VARRAY) An unordered set of elements

CREATE OR REPLACE TYPE NumberTab AS TABLE OF Number;/

CREATE TABLE properties (name     VARCHAR2(20),property_geometry  NumberTab) NESTED TABLE property_geometry

STORE AS geomtab;

Query: SELECT * from TABLE (select * from properties where name=‘CityHall’) t;

Large-Object TypesLarge-Object Types

Large objects (photos, videos, CAD files, etc.) are stored as a large object: blob: binary large object -- object is a large collection of

uninterpreted binary data (whose interpretation is left to an application outside of the database system)

clob: character large object -- object is a large collection of character data

When a query returns a large object, a pointer is returned rather than the large object itself.

Conversion and other FunctionsConversion and other Functions

TO_CHAR Converts numbers, date, time, clob args to char strings

Can specify a format for numbers, dates SELECT TO_CHAR(10000,'L99G999D99MI') "Amount" FROM DUAL

Returns the string: $10,000

TO_NUMBER

TO_DATE,…

SUBSTR: SELECT SUBSTR('ABCDEFG',3,4) "Substring" FROM DUAL;

Returns the string starting at pos 3 and of length 4: ‘CDEF’

INSTR (string, pattern_to_search_for,..) Checks if patterns is in string and returns in pos

TRIM; trims the strings from either ends

SQL as a DDLSQL as a DDL

Using SQL to create logical schemata

Example: CREATE TABLE branch ( bname char(15) NOT NULL, bcity char(30), assets int) attrattr attr-domainsattr-domains

What domains available?

char(n), varchar(n)

int

float(p), numeric(p,d) e.g. numeric(3,1) allows 44.5

real

date: year-mo-day e.g. ‘2004-02-05’ , time: hr:min:sec e.g. ’09:30:01’

precision digits

SQL as DDLSQL as DDL

Can create new domains:

e.g CREATE DOMAIN p-name char(15) NOT NULL

Modify tables:

DROP TABLE <relation> -- drops both schema and instance e.g. DROP TABLE account

ALTER TABLE <relation> ADD ( <attr> <domain>)

ex. ALTER TABLE branch ADD numloans int -- new values given default value of NULL

ALTER TABLE <relation> DROP (<attr>)

ex. ALTER TABLE customer DROP cstreet

AuthorizationAuthorization

Forms of authorization on parts of the database:

Read - allows reading, but not modification of data. Insert - allows insertion of new data, but not modification of

existing data. Update - allows modification, but not deletion of data. Delete - allows deletion of data.

Forms of authorization to modify the database schema (covered in Chapter 8):

Index - allows creation and deletion of indices. Resources - allows creation of new relations. Alteration - allows addition or deletion of attributes in a relation. Drop - allows deletion of relations.

Authorization Specification in SQLAuthorization Specification in SQL

The grant statement is used to confer authorization

grant <privilege list>

on <relation name or view name> to <user list>

<user list> is: a user-id

public, which allows all valid users the privilege granted

A role (more on this in Chapter 8)

Granting a privilege on a view does not imply granting any privileges on the underlying relations.

The grantor of the privilege must already hold the privilege on the specified item (or be the database administrator).

Privileges in SQLPrivileges in SQL

select: allows read access to relation,or the ability to query using the view Example: grant users U1, U2, and U3 select authorization on the branch

relation:

grant select on branch to U1, U2, U3

insert: the ability to insert tuples

update: the ability to update using the SQL update statement

delete: the ability to delete tuples.

all privileges: used as a short form for all the allowable privileges

more in Chapter 8

Revoking Authorization in SQLRevoking Authorization in SQL

The revoke statement is used to revoke authorization.revoke <privilege list>

on <relation name or view name> from <user list>

Example:revoke select on branch from U1, U2, U3

<privilege-list> may be all to revoke all privileges the revokee may hold.

If <revokee-list> includes public, all users lose the privilege except those granted it explicitly.

If the same privilege was granted twice to the same user by different grantees, the user may retain the privilege after the revocation.

All privileges that depend on the privilege being revoked are also revoked.

SQL SummarySQL SummaryQuery Language (DML):

SELECT, FROM, WHEREGROUP BY, HAVINGINTOORDER BYNested Queries (IN, EXISTS, UNIQUE, ALL, SOME, correlation)AggregatesJoinsUpdatesViews, Pseudocolumns, Connect-by

Built-in DatatypesDDL:

CREATE TABLEDROP TABLECREATE DOMAINALTER TABLE

Authorization