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Database application development

(Real SQL programming)

February 27, 2014

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Administrivia Announcements

- PS 4 is ready Reading assignment

- Chapter 6 Today

- Database application development (real SQL programming)

Acknowledgement- Some slide content courtesy of Ramakrishnan, Gehrke, and

Ullman

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SQL in real programs

We have seen mainly how SQL is used at thegeneric query interface- in interactive mode, or- via a script file- (except with JDBC)

Reality is almost always different:- Conventional programs interacting with SQL

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SQL in application code

SQL commands can be called from within a hostlanguage (e.g., C, C++, Java) program

- SQL statements can refer to host language variables(including special variables used to return status)

- Must include a statement to connect to the rightdatabase

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Three options for integration

1. Embed SQL in a host language- Embedded SQL, Dynamic SQL- Ex: SQLJ

2. Create special API to call SQL commands- SQL/CLI- Ex: SQL/CLI for C, JDBC

3. Database stored procedures (code in a specializedlanguage is stored in the database itself)- SQL/PSM

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Impedance mismatch

Differences between programming language model anddatabase model

Binding for each host programming language- Mapping between each SQL attribute type and its compatible

programming language type

SQL relations are (multi-)sets of records, with no a prioribound on the number of records- No such data structure exists in host programming languages

such as C++, Java

- SQL supports a mechanism called a cursor to handle this

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Embedded SQL

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Embedded SQL (static)

Key idea:- Embed SQL in the host language- SQL statements identified by a special prefix- A preprocessor(or precompiler) converts the SQL statements

into special API calls that fit with the surrounding host-languagecode

- Then a regular compiler is used to compile the code All embedded SQL statements begin with EXEC SQL, so

the preprocessor can find them

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Language constructs

Connecting to a databaseEXEC SQL CONNECT

Declaring shared variables: To connect SQL and the host-language program, the two parts must share some variables

EXEC SQL BEGIN DECLARE SECTION

// variables here

EXEC SQL END DECLARE SECTION

StatementsEXEC SQL

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Use of shared variables

In SQL, the shared variables must be preceded by acolon (:)- They may be used as constants provided by the host-language

program- They may get values from SQL statements and pass those

values to the host-language program

In the host language, shared variables behave like anyother variable

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Example: shared variables


char c_sname[20];

long c_sid;

short c_rating;float c_age;


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Communication variables

Two special errorvariables:- SQLCODE (long, is negative if an error has

occurred)

-SQLSTATE (char[6], predefined codes for commonerrors)

One of these two variables must be declared

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Embedded SQL statement

EXEC SQL

INSERT INTO Sailors

VALUES (:c_sname, :c_sid, :c_rating, :c_age);

It is using shared variables

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Example: Looking up prices

Using C with embedded SQL lets us sketch theimportant parts of a function that obtains a beer and abar, and looks up the price of that beer at that bar.

Assumes database has our usual Sells(bar, beer, price)relation

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Example: C plus SQL

EXEC SQL BEGIN DECLARE SECTION;char theBar[21], theBeer[21];float thePrice;

EXEC SQL END DECLARE SECTION;

/* obtain values for theBar and theBeer */EXEC SQL SELECT price INTO :thePrice

FROM Sells

WHERE bar = :theBar AND beer = :theBeer;/* do something with thePrice */

20 chars +

endmarker

SELECT-INTO

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Embedded queries

Embedded SQL has the same limitations asPSM (that we will see later) regarding queries:

- SELECT-INTO for a query guaranteed to produce asingletuple- For multipletuples, we have to use a cursor

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Cursor statements

Declare a cursor cwith:EXEC SQL DECLARE cCURSOR FOR ;

Open and close cursor c with:EXEC SQL OPEN CURSOR c;

EXEC SQL CLOSE CURSOR c;

Fetch from c by:EXEC SQL FETCH c INTO ;

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Example: Print Joes menu

Lets write C + SQL code to print Joes menu the list ofbeer-price pairs that we find in Sells(bar, beer, price)with bar = Joes Bar

A cursor will visit each Sells tuple that has bar = JoesBar

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Example: Declarations

EXEC SQL BEGIN DECLARE SECTION;

char theBeer[21];

float thePrice;


EXEC SQL DECLARE c CURSOR FOR

SELECT beer, price

FROM Sells

WHERE bar = Joes Bar;

The cursor declaration goes

outside the declare-section

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Example: Executable part

EXEC SQL OPEN CURSOR c;

while(1) {

EXEC SQL FETCH c

INTO :theBeer, :thePrice;if (NO_MORE_TUPLES) break;

/* format and print theBeer and

thePrice */

}

EXEC SQL CLOSE CURSOR c;

The C style

of breaking

loops

// Using the following macro:

#define NO_MORE_TUPLES !(strcmp(SQLSTATE, 02000))

// 02000means no tuple was found

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Cursors

A way to deal with impedance mismatch A cursor is essentially a tuple-variable that ranges over all

tuples in the result of some query

Can declare a cursor on a relation or query statement(which generates a relation)

DECLARE c CURSOR FOR ;

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Cursors (cont.)

Can open a cursor, and repeatedly fetch a tuple thenmove the cursor, until all tuples have been retrieved

- Can use a special clause, called ORDER BY, in queries that areaccessed through a cursor, to control the order in which tuplesare returned

Fields in ORDER BY clause must also appear in SELECTclause- The ORDER BY clause, which orders answer tuples, is only

allowed in the context of a cursor

Can also modify/delete the tuple pointed to by a cursor

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Opening and closing cursors

To use cursor c, we must issue the command:OPEN c;

- The query of c is evaluated, and c is set to point to the firsttuple of the result

When finished with c, issue command:CLOSE c;

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Fetching tuples from a cursor

To get the next tuple from cursor c, issue command:FETCH FROM c INTO x1, x2, , xn ;

The xs are a list of variables, one for each component ofthe tuples referred to by c

cis moved automatically to the next tuple

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Breaking cursor loops (1)

The usual way to use a cursor is to create a loop with aFETCH statement, and do something with each tuplefetched

A tricky point is how we get out of the loop when thecursor has no more tuples to deliver

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Each SQL operation returns a status, which is a 5-digitcharacter string- For example, 00000 = Everything OK,and 02000 = Failed to

find a tuple

We can get the value of the status in a variable calledSQLSTATE

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We may declare a condition, which is a boolean variablethat is true if and only if SQLSTATEhas a particularvalue

Example: We can declare condition NotFoundtorepresent 02000 by:

DECLARE NotFound CONDITION FOR

SQLSTATE 02000;

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The structure of a cursor loop is thus:cursorLoop: LOOP

...

FETCH c INTO ... ;

IF NotFound THEN LEAVE cursorLoop;

END IF;

...

END LOOP;

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Cursor that gets names of sailors whovereserved a red boat, in alphabetical order

EXEC SQL DECLARE sinfo CURSOR FOR

SELECT S.sname

FORM Sailors S, Boats B, Reserves R

WHERE S.sid=R.sid AND R.bid=B.bid AND B.color=red

ORDER BY S.sname

Note that it is illegal to replace S.sname by, say, S.sid inthe ORDER BY clause because S.sid does not appear inSELECT!

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Example: Embedding SQL in C

char SQLSTATE[6];EXEC SQL BEGIN DECLARE SECTION

char c_sname[20];

short c_minrating;

float c_age;


c_minrating = random();EXEC SQL DECLARE sinfo CURSOR FOR

SELECT S.sname, S.age

FROM Sailors S

WHERE S.rating > :c_minrating

ORDER BY S.sname;

EXEC SQL OPEN sinfo;do {

EXEC SQL FETCH sinfo INTO :c_sname; :c_age;

printf(%s is %d years old\n, c_sname, c_age);

} while (SQLSTATE != 02000); // 02000means NO DATA

EXEC SQL CLOSE sinfo;

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Need for Dynamic SQL

Most applications use specific queries and modificationstatements to interact with the database- The DBMS compiles EXEC SQL statements into specific

procedure calls and produces an ordinary host-languageprogram that uses a library

What about the query the host language program readsin from the user, which doesnt know what it needs todo until it runs?- SQL query strings are not always known at compile time- E.g., spreadsheet or a graphical DBMS frontend allowsconstruction of SQL statements on-the-fly

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Dynamic SQL example

char c_sqlstring[] =

{DELETE FROM Sailors WHERE rating>5}

EXEC SQL PREPARE readytogo FROM :c_sqlstring;

EXEC SQL EXECUTE readytogo;

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Dynamic SQL constructs

Preparing a query:EXEC SQL PREPARE

FROM ;

Executing a query:EXEC SQL EXECUTE ;

Prepare= optimizequery Prepare once, execute many times

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Example: A generic interface


char query[MAX_LENGTH];


while(1) {

/* issue SQL> prompt */

/* read users query into array query */

EXEC SQL PREPARE q FROM :query;

EXEC SQL EXECUTE q;

} q is an SQL variablerepresenting the optimized

form of whatever statement

is typed into :query

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Execute-immediate

If we are only going to execute the query once, we cancombine the PREPARE and EXECUTE steps into one

Use:EXEC SQL EXECUTE IMMEDIATE ;

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Example: Generic interface again


char query[MAX_LENGTH];


while(1) {/* issue SQL> prompt */

/* read users query into array query */

EXEC SQL EXECUTE IMMEDIATE :query;

}

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Call-Level Interface (CLI)Alternative to embedding

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Call-Level Interface (CLI)

Rather than modify compiler, add library with databasecalls (API)

Special standardized interface: procedures/objects Pass SQL strings from language, presents result sets in a

language-friendly way

SQL/CLI Suns JDBC: Java API Supposedly DBMS-neutral

- A drivertraps the calls and translates them into DBMS-specificcode

- Database can be across a network

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JDBC architecture

Four architectural components:

Application- initiates and terminates connections- submits SQL statements

Driver manager- Loads JDBC driver

Driver- Connects to data source- Transmits requests and- Returns/translates results and error codes

Data source- Processes SQL statements

Will skip JDBCsince weve

already studied it.

I will leave these

slides in for yourreference though.

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JDBC architecture (cont.)

Four types of drivers Bridge

- Translates SQL commands into non-native API- Ex: JDBC-ODBC bridge (code for ODBC and JDBC driver needs to be

available on each client)

Direct translation to native API via non-Java driver- Translates SQL commands to native API of data source- Needs OS-specific binary on each client

Network bridge- Sends commands over the network to a middleware server that talks to

the data source.- Needs only small JDBC driver at each client

Direct translation to native API via Java driver- Converts JDBC calls directly to network protocol used by DBMS- Needs DBMS-specific Java driver at each client

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JDBC classes and interfaces

Steps to submit a database query

Load the JDBC driver Connect to the data source

Execute SQL statements

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JDBC driver management

All drivers are managed by the DriverManager class Loading a JDBC driver

- In the Java codeClass.forName(oracle.jdbc.driver.OracleDriver);

Class.forName(com.mysql.jdbc.Driver);

-When starting the Java application-Djdbc.drivers=oracle.jdbc.driver

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Connections in JDBC

We interact with a data source through sessions- Each connection identifies a logical session

JDBC URL:- Jdbc:.

Example:String url=jdbc:oracle:www.bookstore.com:3083;

Connection con;

try {

con = DriverManager.getConnection(url,userid,passwd);

} catch SQLException excpt { . . . }

// MySQL example:

DriverManager.getConnection(

"jdbc:mysql://localhost:3306/bookstore", //database name

"alee", // username

allowme"); // password

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Connection class interface

public int getTransactionIsolation()

public void setTransactionIsolation(int level)- Sets isolation level for the current connection

public boolean getReadOnly()

public void setReadOnly(boolean b)- Specifies whether transactions in this connection are read-only

public boolean getAutoCommit()

public void setAutoCommit(boolean b)- If autocommit is set, then each SQL statement is considered its own

transaction

- Otherwise, a transaction is committed using commit(), or aborted usingrollback()

public boolean isClosed()

- Checks whether connection is still open

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Executing SQL statements

Three different ways of executing SQL statements- Statement

Both static and dynamic SQL statements- PreparedStatement

Semi-static SQL statements- CallableStatement

Stored procedures PreparedStatement class

- Precompiled, parameterized SQL statements Structure is fixed Values of parameters are determined at run-time

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Executing SQL statements (cont.)

String sql=INSERT INTO Sailors VALUES(?,?,?,?);

PreparedStatement pstmt=con.prepareStatement(sql);

pstmt.clearParameters();

pstmt.setInt(1, sid);

pstmt.setString(2, sname);pstmt.setInt(3, rating);

pstmt.setFloat(4, age);

// No rows are returned so use executeUpdate (insert, update, alter,

// delete)// Use executeQuery if it returns rows (select)

int numRows = pstmt.executeUpdate();

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ResultSets

PreparedStatement.executeUpdate only returns thenumber of affected records

PreparedStatement.executeQuery returns data,encapsulated in a ResultSet object (a cursor)

ResultSet rs=pstmt.executeQuery(sql);

// rs is now a cursor

while (rs.next()) {

// process the data

}

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ResultSets (cont.)

A ResultSet is a very powerful cursor

previous()- moves one row back

absolute(int num)- moves to the row with the specified number

relative(int num)- moves forward or backward

first() last()

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Example: ResultSet

String query = SELECT ;

ResultSet rs = stmt.executeQuery(query);

while (rs.next()) {

isbn = rs.getString(1);title = rs.getString(TITLE);

// process isbn and title

}

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Matching Java and SQL data types

SQL Type Java class ResultSet get method

BIT Boolean getBoolean()

CHAR String getString()

VARCHAR String getString()

DOUBLE Double getDouble()FLOAT Double getDouble()

INTEGER Integer getInt()

REAL Double getFloat()

DATE Java.sql.Date getDate()

TIME Java.sql.Time getTime()TIMESTAMP Java.sql.TimeStamp getTimestamp()

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JDBC: exceptions and warning

Most ofjava.sql can throw an SQLException if an erroroccurs (cf. SQLSTATE)

SQLWarning is a subclass of SQLException- Not as severe- They are not thrown and their existence has to be explicitly tested

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Warning and exceptions (cont.)

try {

stmt=con.createStatement();

warning=con.getWarnings();

while (warning != null) {

// handle SQLWarnings

warning = warning.getNextWarning();}

con.clearWarnings();

stmt.executeUpdate(queryString);

warning = con.getWarnings();

}

catch (SQLException sqle) {

// handle the exception

}

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Examining database metadata

DatabaseMetaData object gives information about thedatabase system and the catalog

DatabaseMetaData md = con.getMetaData();

// print information about the driverSystem.out.println(Name: + md.getDriverName() +

version: + md.getDriverVersion());

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Database metadata (cont.)

DatabaseMetaData md = con.getMetaData();ResultSet trs=md.getTables(null,null,null,null);

String tableName;

while (trs.next()) {

tableName = trs.getString(TABLE_NAME);

System.out.println(Table: + tableName);

// prints all attributesResultSet crs = md.getColumns(null,null,tableName,null);

while (crs.next()) {

System.out.println(crs.getString(COLUMN_NAME) + );

}

// prints out the primary keys of this table

System.out.println(The keys of table + tableName + are:);

ResultSet krs = md.getPrimaryKeys(null,null,tableName);

while (krs.next()) {

System.out.println(krs.getString(COLUMN_NAME) + );

}

}

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A (semi-)complete example

Connection con = // connectDriverManager.getConnection(url,login, passwd);

Statement stmt = con.createStatement(); // set up stmt

String query = SELECT name, rating FROM Sailors;

ResultSet rs = stmt.executeQuery(query);

try {

while (rs.next()) { // loop through result tuplesString s = rs.getString(name);

int n = rs.getInt(rating);

System.out.println(s + + n);

}

}

catch (SQLException ex) {

System.out.println(ex.getMessage() + +

ex.getSQLState() + +

ex.getErrorCode());

}

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CLI Examples for C and Java

See a complete example each for both Java and C See DB.java and Bank1.java from an earlier lecture on

JDBC for Java

See cmysql.c for C

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SQLJ

SQLJ should really be in the Embedded SQL section ofthis slide set, but I located it here so that you cancompare it with JDBC

Embedded SQL with Java

Preprocessor for SQLJ into Java Complements JDBC with a semi-static query model SQLJ (part of the SQL standard) versus embedded SQL(vendor-specific) [I am providing these slides for SQLJ, but we wont go

over them in class. Its an optional topic.]

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SQLJ vs. JDBC

With SQLJ, compilers can perform syntax checks, strongtype checks, consistency of the query with the schema- All arguments always bound to the same variable

#sql = { SELECT name, rating INTO :name, :rating

FROM BooksWHERE sid = :sid;

}

- Compare to JDBCSid = rs.getInt(1);

if (sid==1)

sname1 = rs.getString(2);

else

sname2 = rs.getString(2);

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SQLJ codeInt sid; Sting name; Int rating;

// 1. Declare the iterator class (cursor!)

#sql iterator Sailors(Int sid, String name, Int rating);

// 2. Instantiate an iterator object

Sailors sailors;

// 3. Initialize the iterator#sql sailors = {

SELECT sid, sname INTO :sid, :name

FROM Sailors

WHERE rating = :rating

};

// 4. Retrieve results

while (sailors.next()) {

System.out.println(sailors.sid + + sailors.sname));

}

// 5. Close the iterator object

sailors.close();

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Corresponding JDBC code

PreparedStatement stmt = connection.prepareStatement(SELECT sid, sname FROM Sailors WHERE rating=?);

// set the parameter in the query and execute it

stmt.setInt(1, rating);

ResultSet rs = stmt.executeQuery();

// retrieve the results

while (rs.next()) {

System.out.println(rs.getInt(1) + + rs.getString(2));

}

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SQLJ iterators

Two types of iterators (cursors) Named iterator

- Need both variable type and name, and then allows retrieval of columns by name- See example two slides ago

Positional iterator- Need only variable type, and then uses FETCH INTO construct#sql iterator Sailors(Int, String, Int);

Sailors sailors;

#sailors = . . .

while (true) {

#sql {FETCH :sailors INTO :sid, :name, :rating};

if (sailors.endFetch()) {

break;

}

// process the sailor

}

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Stored Procedures

Alternative to Embedding and CLI

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Stored Procedures

PSM (Persistent Stored Modules) allows us to storeprocedures as database schema elements (SQL:2003)

A stored procedure is- A program executed through a single SQL statement- Executed in the process space of the server- PSM = a mixture of conventional statements (if, while, etc.) and SQL

Advantages- Lets us do things we cannot do in SQL alone- Can encapsulate application logic while staying closeto the data- Reuse of application logic by different users- Avoid tuple-at-a-time return of records through cursors

Most DBMSs allow users to write stored procedures in asimple, general-purpose language (close to SQL)- A SQL/PSM standard is a representative

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Basic PSM Form

CREATE PROCEDURE (

)

;

Function alternative:CREATE FUNCTION (

) RETURNS

;

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Parameters in PSM

Unlike the usual name-type pairs in languages like C,PSM uses mode-name-type triples, where the mode canbe:

- IN= procedure uses value, does not change value- OUT= procedure changes, does not use- INOUT= both

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Example: Stored procedure (next)

Lets write a procedure that takes two arguments b andp, and adds a tuple to Sells(bar, beer, price)that has bar= Joes Bar, beer = b, and price =p

- Used by Joe to add to his menu more easily

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The procedure (definition)

CREATE PROCEDURE JoeMenu (

IN b CHAR(20),

IN p REAL

)

INSERT INTO Sells

VALUES(Joes Bar, b, p);

Parameters are both

read-only, not changed

The body a

single insertion

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Invokingprocedures

Use SQL/PSM statement CALL, with the name of thedesired procedure and actual arguments

Example:CALL JoeMenu(Moosedrool, 5.00);

Functions used in SQL expressions wherever a value oftheir return type is appropriate

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Kinds of PSM statements (1)

RETURN sets the return value of afunction- Unlike C, etc., RETURN doesnot terminate function execution

DECLARE used to declare localvariables BEGIN . . . ENDfor groups of statements

- Separate statements by semicolons Not surprising it requires most of the language

constructs in this language too. After all, you needthose to create functions as in any language powerfulenough to support functions!!!

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Kinds of PSM statements (2)

Assignment statements:SET = ;- Example: SET b = Bud;

Statement labels: give a statement a label by prefixing aname and a colon

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IF statements

Simplest form:IF THEN

END IF; Add ELSE if desired, as

IF . . . THEN . . . ELSE . . . END IF;

Add additional cases by ELSEIF :IF THEN ELSEIF THEN ELSEIF THEN ELSE END IF;

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Example: IF

Lets rate bars by how many customers they have,based on Frequents(drinker,bar)- = 200 customers: popular

Function Rate(b)rates bar b

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Example: IF (cont.)

CREATE FUNCTION Rate (IN b CHAR(20) )RETURNS CHAR(10)DECLARE cust INTEGER;

BEGIN

SET cust = (SELECT COUNT(*) FROM FrequentsWHERE bar = b);IF cust < 100 THEN RETURN unpopularELSEIF cust < 200 THEN RETURN averageELSE RETURN popularEND IF;

END;

Number of

customers of

bar b

Return occurs here, not at

one of the RETURN statements

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Loops

Basic form:: LOOP

END LOOP;

Exit from a loop by:LEAVE

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Example: Exiting a loop

loop1: LOOP

. . .

LEAVE loop1;

. . .

END LOOP;

If this statement is executed . . .

Control winds up here

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Other loop forms

WHILE DO

END WHILE;

REPEAT UNTIL

END REPEAT;

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1. Queries

General SELECT-FROM-WHERE queries are notpermitted in PSM

There are three ways to get the effect of a query:1. Queries producing one value can be the expression in an

assignment

2. Single-row SELECT . . . INTO3. Can use cursors naturally without EXEC SQL

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Example: Assignment/Query

Using local variablep and Sells(bar, beer, price), wecan get the price Joe charges for Bud by:

SET p = (SELECT priceFROM Sells

WHERE bar = Joes BarAND

beer = Bud);

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2. SELECT . . . INTO

Another way to get the value of a query that returnsone tuple is by placing INTO after theSELECT clause.

Example:SELECTprice INTOp

FROM Sells

WHERE bar =Joe

s Bar

AND

beer = Bud;

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3. Cursor

Lets write a procedure that examines Sells(bar, beer,price), and raises by $1 the price of all beers at Joes Barthat are under $3

- Yes, we could write this as a simple UPDATE, but the detailsare instructive anyway

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The needed declarations

CREATE PROCEDURE JoeGouge( )

DECLARE theBeer CHAR(20);

DECLARE thePrice REAL;

DECLARE NotFound CONDITION FORSQLSTATE 02000;

DECLARE c CURSOR FOR

(SELECT beer, price

FROM SellsWHERE bar = Joes Bar);

Used to hold

beer-price pairs

when fetching

through cursor c

Returns Joes menu

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The procedure body

BEGIN

OPEN c;

menuLoop: LOOPFETCH c INTO theBeer, thePrice;

IF NotFound THEN LEAVE menuLoop END IF;

IF thePrice < 3.00 THENUPDATE Sells SET price = thePrice + 1.00

WHERE bar = Joes BarAND beer = theBeer;

END IF;END LOOP;

CLOSE c;

END;

Check if the recent

FETCH failed to

get a tuple

If Joe charges less than $3 forthe beer, raise its price at

Joes Bar by $1

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More examples

CREATE PROCEDURE ShowNumReservations

SELECT S.sid, S.sname, COUNT(*)

FROM Sailors S, Reserves R

WHERE S.sid = R.sid

GROUP BY S.sid, S.sname

CREATE PROCEDURE IncreaseRating(

IN sailorId INTEGER, IN increase INTEGER)

UPDATE Sailors

SET rating = rating + increase

WHERE sid = sailorId

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Stored procedures in any language

Stored procedures do not have to be written in SQLCREATE PROCEDURE TopSailors (IN num INTEGER)

LANGUAGE JAVAEXTERNAL NAME file://c:/storedProcs/rank.jar

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Example: Calling stored procedures


Int sid;

Int rating;


// now increase the rating of this sailor

EXEC CALL IncreaseRating(:sid, :rating);

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Ex: Calling stored procedures (cont.)

JDBC:

CallableStatement cstmt=con.prepareCall({call ShowSailors});

ResultSet rs=cstmt.executeQuery();

while (rs.next()) { . . . }

SQLJ:

#sql Iterator ShowSailors(. . .);

ShowSailors showsailors;#sql showsailors={CALL ShowSailors};

while (showsailors.next()) { . . . }

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Example: function

CREATE FUNCTION rateSailor(IN sailorId INTEGER)

RETURNS INTEGER

DECALRE rating INTEGER

DECLARE numRes INTEGER

SET numRes = (SELECT COUNT(*)FROM Reserves R

WHERE R.sid = sailorId)

IF (numRes > 10)

THEN rating = 1;

ELSE rating = 0;

END IF;

RETURN rating;

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Summary of SQL/PSM constructs

Local variables (DECLARE) RETURN values for FUNCTION Assign variables with SET Branches and loops

- IF () THEN ;ELSEIF () THEN ;

. . . ELSE ;

END IF;

- LOOP ;END LOOP;

Queries can be parts of expressions Can use cursors naturally without EXEC SQL

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Summary

Embedded SQL allows execution of parameterized staticqueries within a host language

Dynamic SQL allows execution of completely ad hocqueries within a host language

Cursor mechanism allows retrieval of one record at atime and bridges impedance mismatch between hostlanguage and SQL

APIs such as JDBC introduce a layer of abstractionbetween application and DBMS

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Summary (cont.)

SQLJ: static model, queries checked at compile-time Stored procedures execute application logic directly at

the server

SQL/PSM standard for writing stored procedures

Date post:	13-Apr-2018
Category:	Documents
Upload:	maria-estrada
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