SQL: Data Sub Language

Transcription

1 SQL: Data Sub Language

2 SQL used with regular Language SQL used to deal with the database Stores/Updates data Retrieves data Regular language deals with other aspects of the program: Makes beautiful web page Asks for/validates user input Charges payments to user s credit card

3 Main Problems Get SQL values into Program variables E.g.: get item description from DB to web page Get Program values into SQL statements E.g.: check login/pw with DB. Handling Set valued results in Host Language: no Table type. E.g.: display all items matching query for digital camera in New Egg catalog.

4 PL/SQL General purpose programming language similar to Pascal or ADA SQL built into the language. Makes host variable issues easy Same datatypes as SQL Focus on handling set valued results Special cursor handling features

5 Iterate Thru Results: Cursor Opening cursor executes query positions pointer at top of result Loop to retrieve successive rows FETCH x INTO vars; Close Cursor

6 Iterate Thru Results: Cursor Opening cursor executes query positions pointer at top of result Loop to retrieve successive rows FETCH x INTO vars; Close Cursor Like using a file

7 Iterate Thru Results: Cursor Opening cursor executes query positions pointer at top of result Loop to retrieve successive rows FETCH x INTO vars; Close Cursor Like using a file Open it for reading

8 Iterate Thru Results: Cursor Opening cursor executes query positions pointer at top of result Loop to retrieve successive rows FETCH x INTO vars; Close Cursor Like using a file Open it for reading Loop through it

9 Iterate Thru Results: Cursor Opening cursor executes query positions pointer at top of result Loop to retrieve successive rows FETCH x INTO vars; Close Cursor Like using a file Open it for reading Loop through it Close when done

10 Cursor Snippet in PL/SQL DECLARE deptnum integer; cursor Empname is SELECT fname, lname FROM employee WHERE dno = deptnum; BEGIN END;

11 Cursor Snippet in PL/SQL DECLARE deptnum integer; cursor Empname is SELECT fname, lname FROM employee WHERE dno = deptnum; BEGIN END; Cursor: named query

12 Cursor Snippet in PL/SQL DECLARE deptnum integer; cursor Empname is SELECT fname, lname FROM employee WHERE dno = deptnum; BEGIN END; Only Program Variable

13 Cursor Snippet in PL/SQL DECLARE deptnum integer; cursor Empname is SELECT fname, lname FROM employee WHERE dno = deptnum; BEGIN END; Database Objects

14 Cursor Snippet in PL/SQL DECLARE deptnum integer; cursor Empname is SELECT fname, lname FROM employee WHERE dno = deptnum; BEGIN END; Database Objects So we got deptnum into the query but still have to get fname and lname out of it into variables.

15 Cursor Snippet in PL/SQL DECLARE deptnum integer; Vfname, Vlname varchar2 (20); cursor Empname is ; -- see prev. BEGIN open Empname; fetch Empname into Vfname,Vlname; while Empname%found loop -- do something w/fname,lname fetch Empname into fname,lname; end loop; close Empname; END;

16 Cursor Snippet in PL/SQL DECLARE deptnum integer; Vfname, Vlname varchar2 (20); cursor Empname is ; -- see prev. BEGIN open Empname; fetch Empname into Vfname,Vlname; while Empname%found loop -- do something w/fname,lname fetch Empname into fname,lname; end loop; close Empname; END; Use cursor just like file

17 Cursor Snippet in PL/SQL DECLARE deptnum integer; Vfname, Vlname varchar2 (20); cursor Empname is ; -- see prev. BEGIN open Empname; fetch Empname into Vfname,Vlname; while Empname%found loop -- do something w/fname,lname fetch Empname into fname,lname; end loop; close Empname; END; Variables to receive DB info with fetch into construct.

18 Cursor Snippet in PL/SQL DECLARE deptnum integer; Vfname, Vlname varchar2 (20); cursor Empname is ; -- see prev. BEGIN open Empname; fetch Empname into Vfname,Vlname; while Empname%found loop -- do something w/fname,lname fetch Empname into fname,lname; end loop; close Empname; END; Like check for end of file

19 Cursor Interpolates When Used BEGIN deptnum := 5; open empname; --cursor looks for 5 s close empname; deptnum := 7; open empname; --now it looks for 7 s

20 Query as String PL/SQL: SQL tightly coupled with host. Many languages: SQL loosely coupled. Query created as a string String compiled and executed on server Results available to program one row at a time Behavior still follows the Cursor model. Still need to get data into and out of DB and program.

21 PHP Intro PHP variables not declared, just used. PHP variables all begin with $ sign, PHP variables interpolated into strings: $myname = "George"; $mystring = "Hello $myname"; print $mystring; # output: Hello George

22 PHP Snippet: Query String $deptnum=22; $query="select fname, lname FROM employee WHERE dno = $deptnum"; Note: $query does not behave like a cursor declaration. 22 has been interpolated and will not change even if $deptnum changes.

23 PHP Snippet: Send to DB and process (MDB2 library) $result =& $con->query($query); while ($arr = $result->fetchrow()){ // process each field of the // row in $arr } $result->free();

24 PHP Snippet: Send to DB and process (MDB2 library) $result =& $con->query($query); while ($arr = $result->fetchrow()){ // process each field of the // row in $arr } $result->free(); $con is the connection object. This sends the query string to the DB for compilation and execution.

25 PHP Snippet: Send to DB and process (MDB2 library) $result =& $con->query($query); while ($arr = $result->fetchrow()){ // process each field of the // row in $arr } $result->free(); $result acts like an opened cursor. Called a result set. Provides methods like fetchrow() to access tuples sequentially.

26 Use prepare to get Cursor Behavior Query string is prepared by being sent to database with placeholders for program variables. Before execution, placeholder is bound to a real program variable. Execution sends prepared query plus values of bound variables for execution.

27 PHP snippet (oci8 library) $query=oci_parse( "SELECT fname, lname FROM employee WHERE dno = :dnumber"); oci_bind_by_name($query, ":dnumber", $deptnum, 32); oci_execute($query);

28 PHP snippet (oci8 library) $query=oci_parse( "SELECT fname, lname FROM employee WHERE dno = :dnumber"); oci_bind_by_name($query, ":dnumber", $deptnum, 32); oci_execute($query); :dnumber in the string represents a program variable. It is bound to $deptnum. Each time $query is executed, it picks up the current value of $deptnum.

29 PHP Snippet (oci8) while ($row = oci_fetch_row($query)){ // do something with $row }

30 Cursor Snippet in PL/SQL cursor Empname is SELECT fname, lname FROM employee WHERE dno = deptnum; BEGIN for rec in Empname loop end loop; END;

31 Opens, loops, and closes in one statement Cursor Snippet in PL/SQL cursor Empname is SELECT fname, lname FROM employee WHERE dno = deptnum; BEGIN for rec in Empname loop end loop; END;

32 Opens, loops, and closes in one statement Cursor Snippet in PL/SQL cursor Empname is SELECT fname, lname FROM employee WHERE dno = deptnum; BEGIN for rec in Empname loop end loop; END; Record variable, local to the loop.