Advanced Database System - Ch04

An Introduction to SQLAn Introduction to SQL

Prof. Yin-Fu HuangProf. Yin-Fu HuangCSIE, NYUST CSIE, NYUST

Chapter 4Chapter 4

Advanced Database System Yin-Fu Huang

4.14.1 IntroductionIntroduction

SQL:1999 Products typically support what might be called “a

superset of a subset” of the standard.e.g. IBM DB2


4.24.2 OverviewOverview

Data definition operations (See Fig. 4.1)


InsertInto Temp(P#, Weight) Select P#, Weight From P Where Color=Color(‘Red’);

DeleteFrom SpWhere P#=P#(’P2’);

Update SSet Status=Status*2, City=‘Rome’ Where City=‘Paris’;

Data manipulation operations (See Fig. 4.2)

4.24.2 Overview (Cont.)Overview (Cont.)


Information SchemaSQL catalog vs. SQL schema

4.34.3 The CatalogThe Catalog


4.44.4 ViewsViews

Example: Create View Good_Supplier As Select S#, Status, City From S Where Status > 15;

Select S#, Status From Good_Supplier Where City=’London’;

Select S#, Status

From S Where Status > 15 And City=’London’;


4.54.5 TransactionsTransactions Statements: Start Transaction, Commit Work,

Rollback Work

4.64.6 Embedded SQLEmbedded SQL

The dual-mode principle is that any SQL statement that can be used interactively can also be embedded in an application program; Its converse is not.

Example (See Fig. 4.3)


EXEC SQL executable and declarative SQL statements host variables Into clauses declare sections host variable Sqlstate

host variables appropriate data type⇒ host variables and SQL columns

⇒ the same name EXEC SQL Whenever <condition> <action>;

⇒ a directive to the SQL compiler loose coupling


4.64.6 Embedded SQL (Cont.)Embedded SQL (Cont.)

It is necessary to provide some kind of bridge between the set-level retrieval capacities of SQL and the row-level retrieval capacities of the host. Such is the purpose of cursors.

Operations Not Involving Cursors

Exam: Singleton Select EXEC SQL Select Status, City

Into :Rank, :TownFrom SWhere S#=S#(:Givens#);

Exam: Insert EXEC SQL Insert Into P(P#, Pname, Weight)

Values (:P#, :Pname, :Pwt);

Exam: Delete EXEC SQL Delete

From SpWhere :City= (Select City From S Where S.S#=Sp.S#);

Exam: Update EXEC SQL Update S

Set Status=Status+:RaiseWhere City=‘London’;


4.64.6 Embedded SQL (Cont.)Embedded SQL (Cont.) Operations Involving Cursors

Declare cursor statementEXEC SQL Declare <cursor name> Cursor

For <table expression> [<ordering>];

Open StatementEXEC SQL Open <cursor name>; Active set

Fetch StatementEXEC SQL Fetch <cursor name>

Into <host variable reference commalist>; Close Statement

EXEC SQL Close <cursor name>; Changing the values of host variables no effect⇒


Current forms of Delete and Updatee.g. EXEC SQL Update S

Set Status = Status +:RaiseWhere Current Of X;

Example (Fig. 4.4)Example (Fig. 4.4)


4.74.7 Dynamic SQL and SQL/CLIDynamic SQL and SQL/CLI The steps of an online application:

1. Accept a command from the terminal 2. Analyze that command 3. Execute appropriate SQL statements on the database 4. Return a message and/or results to the terminal

Dynamic SQL Dynamic SQL consists of a set of “dynamic statements”---which themselves a

re compiled ahead of time---whose purpose is precisely to support the compilation and execution of regular SQL statements that are constructed at run time.

Prepare and Execute statementse.g. DCL Sqlsource Char Varying (65000);

Sqlsource = ‘Delete From Sp Where Qty < Qty(300)’;EXEC SQL Prepare Sqlprepped From :Sqlsource;EXEC SQL Execute Sqlprepped;


4.74.7 Dynamic SQL and SQL/CLI (Cont.)Dynamic SQL and SQL/CLI (Cont.) Call-Level Interfaces

SQL/CLI permits an application written in one of the usual host languages to issue database requests, not via embedded SQL, but rather by invoking certain vendor-provided routines.

Those routines use dynamic SQL to perform the requested database operations on the application’s behalf.

Reasons:1. SQL/CLI standardizes the details of certain routine invocations.2. Those applications can be DBMS-independent.

e.g. char sqlsource [65000];strcpy(sqlsource, “Delete From Sp Where Qty < Qty(300)”);rc = SQLExecDirect(hstmt, (SQLCHAR *)sqlsource, SQL_NTS);


4.84.8 SQL Is Not Perfect

There is no product on the market today that supports the relational model in its entirety.


The End.

Technology

Advanced Database System - Ch04