31-08-2007noea/it - fen: databases/sql1 sql – part 1 sql: ddl and dml

31-08-2007 NOEA/IT - FEN: Databases/SQL 1

SQL – part 1

SQL:

DDL and DML


Realisation of the Relational Model: SQL-based DBMSs

(SQL = Structured Query Language)

• SQL is much more than merely queries – it includes– DDL

• Data Definition Language– DML

• Data Manipulation Language– DCL

• Data Control Language


SQL-Versions

• SQL has been implemented by many different DBMS-

manufactures

• SQL is to a large extend the same for most DBMSs – close to a

de facto standard

• Standards:

SQL86 (SQL1), SQL89 (SQL1½), SQL92 (SQL2), SQL3

(SQL9x/SQL2000? - eventually SQL-99)

• SQL2 is still the most common standard.

• SQL-99 is the newest standard (released in 2002)

• Most manufactures have their own extensions (and omissions)

to the standard


SQL2 - DDL

Supports domains:– Basic types, INT, CHAR, strings etc.– Date-Time– Programmer defined types:

CREATE DOMAIN cprType AS CHAR(10);CREATE DOMAIN postalType AS CHAR(4);

Types allows the compiler/interpreter to check for some logical errors

Not in MS SQL Server 2000


SQL2 - DDL

CREATE TABLE Client (

cprno cprType NOT NULL,

….

postCode postalType,

…,

CONSTRAINT ClientPK

PRIMARY KEY(cprno),

CONSTRAINT PCodeCityFK

FOREIGN KEY(postCode) REFERENCES PCodeCity(pCode)

ON UPDATE CASCADE ON DELETE SET NULL);

Should make NOT NULL

unnecessary


SQL2 - DDL

CREATE TABLE PCodeCity (

pCode postalType NOT NULL,

city VARCHAR(30) NOT NULL,

CONSTRAINT PCodeCityPK

PRIMARY KEY(pCode));

Also see Elmasri figure 8.1 and 8.2


SQL2 - DDL

• DROP SCHEMA

• DROP TABLE

• ALTER TABLE

• ALTER TABLE– DROP CONSTRAINT– ADD CONSTRAINT


SQL2 - DML

SELECT

UPDATE

INSERT

DELETE


SQL2 – DML: SELECT

Queries:

SELECT <attribute-list>

FROM <tables>

[WHERE <condition>]

[GROUP BY <attribute-list>]

[HAVING <condition>]

[ORDER BY <attribute-list>]

[...]: WHERE, GROUP BY, HAVING and ORDER BY may be omitted.


The Company Database


Company on SQL Server

• Script:


Relational Algebra - Overview


SQL2 - DML

(Q0): Row and coulomb selection:

SELECT BDATE, ADDRESS

FROM EMPLOYEE

WHERE FNAME = ’John’ AND MINIT = ’B’

AND LNAME = ’Smith’

All attributes:

SELECT *

----


SQL2 - DML

(Q1): JOIN:SELECT FNAME, LNAME, ADDRESS

FROM EMPLOYEE, DEPARTMENT

WHERE DNAME = ’Research’

AND DNO = DNUMBER

Last term in the WHERE-clause is the join-condition.

If omitted the result will be the Cartesian product.


SQL2 - DML

(Q2): JOIN several tables:

SELECT PNUMBER, DNUM, LNAME, ADDRESS

FROM PROJECT, EMPLOYEE, DEPARTMENT

WHERE PLOCATION = ’Stafford’

AND DNUM = DNUMBER

AND SSN = MGRSSN

Note: Two join-conditions in the WHERE-clause.


SQL2 - DML(Q8): Ambiguous attribute names and aliases:

SELECT E.FNAME, E.LNAME,

S.FNAME, S.LNAME

FROM EMPLOYEE E, EMPLOYEE S

WHERE E.SUPERSNN = S.SSN

EMPLOYEE is joined with itself using the aliases E and S.

’.’ (”dot”)-notation may also be used to resolve ambiguous attribute names.


SQL2 - DML

SQL-tables are NOT sets (in the math sense of the word set):

(Q11): SELECT SALARY

FROM EMPLOYEE

(Q11A): SELECT DISTINCT SALARY

FROM EMPLOYEE


SQL2 - DML

(Q4): Set operations:

(SELECT PNUMBERFROM PROJECT, DEPARTMENT, EMPLOYEEWHERE LNAME = ’Smith’ AND

DNUM = DNUMBER AND MGRSSN = SSN)

UNION(SELECT PNUMBERFROM PROJECT, WORKS_ON, EMPLOYEEWHERE LNAME = ’Smith’ AND

PNO = PNUMBER AND ESSN = SSN)

Returns a set!!! (also INTERSECT and EXCEPT)


SQL2 - DML

Updates:– Inserting rows: INSERT– Deleting rows: DELETE– Updating row values: UPDATE

As SELECT they work on tables.


SQL2 - DML

Inserting a single row:INSERT INTO EMPLOYEEVALUES (’Richard’,’K’,’Marini’,’653298653’,

’30-DEC-52’,’98 Oak Forest, Katy,’TX’,’M’,37000,’987654321’,4)

Inserting a single row, only selected attributes:INSERT INTO EMPLOYEE(FNAME,LNAME,SSN)VALUES (’Richard’,’Marini’,’653298653’)

Is rejected if any of the other attributes is defined NOT NULLand doesn’t have defined a default value.


SQL2 - DMLInserting using sub SELECTs:

CREATE TABLE DEPTS_INFO (DEPT_NAME VARCHAR(15),NO_OF_EMPS INTEGER,TOTAL_SAL INTEGER);

INSERT INTO DEPTS_INFOSELECT DNAME, COUNT(*),

SUM(SALARY)FROM DEPARTMENT, EMPLOYEEWHERE DNUMBER = DNOGROUP BY DNAME;

Note DEPTS_INFO is not automatically updated if changes are made in the othe tables. It is a base table.


SQL2 - DML

Deleting rows:DELETE FROM EMPLOYEE

WHERE LNAME =’Brown’

DELETE FROM EMPLOYEE

WHERE SSN = ’123456789’


WHERE DNO IN (SELECT DNUMBER

FROM DEPARTMENT

WHERE DNAME = ’Research’)


(Not equivalent to: ´DROP TABLE EMPLOYEE’. Why not?)


SQL2 - DMLUpdating rows:

UPDATE PROJECT

SET PLOCATION = ’Bellaire’, DNUM = 5

WHERE PNUMBER = 10

UPDATE EMPLOYEE

SET SALARY = SALARY*1.1

WHERE DNO IN(SELECT DNUMBER

FROM DEPARTMENT

WHERE DNAME = ’Research’)

Note, that it is only possible to affect one table in one UPDATE statement.


Exercises

1. The Company Database:1. Run the CREATE-scripts on MS SQL Server

2. Do some of examples in Elmasri chapter 8

2. To which extend does SQL Server obey to the standard? Can you find any divergences?

3. The VW Database:1. Run the CREATE-scripts

2. Implement the queries from vwDatabase.pdf in SQL

31-08-2007noea/it - fen: databases/sql1 sql – part 1 sql: ddl and dml

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