Embedding SQL in High Level Language Programs

Transcription

1 Embedding SQL in High Level Language Programs Alison Butterill IBM i Product Manager Power Systems Agenda Introduction Basic SQL within a HLL program Processing multiple records Error detection Dynamic SQL Tips and Techniques Summary 2 1

2 What is SQL? SQL - Structured Query Language Data language for manipulation of a Relational database English keyword-oriented Excellent tool for application development environment Query Data definition Data manipulation Data control Powerful language for Set-At-A-Time processing SQL is NOT an end user query product! 3 Executing SQL on IBM i Interactive SQL Embedded or compiled in application programs Query Manager SQL Statement Processor Operations Navigator Dynamic SQL SQL Procedure Language Extended Dynamic SQL ODBC, JDBC JSQL or SQLJ X/Open SQL Call Level Interface 4 2

3 V5 SQL Support... Part 1: DB2 Database Manager Included with IBM i (operating system) V5: 5722-SS1 SQL parser and run time support SQL license (5722-ST1) not required to run SQL applications Support for compiled programs using embedded SQL SQL APIs QSQPRCED - Provides extended dynamic SQL capability QSQCHKS - Provides syntax checking for SQL statements X/Open SQL Call Level Interface V5R1 - SQL Statement Processor RUNSQLSTM Command 5 V5 SQL Support Part 2: DB2 for IBM i Query Manager & SQL Development Kit Program number 5722-ST1 Query Manager Interactive SQL SQL precompilers Required for embedding SQL in HLL programs More later SQL REXX interface 6 3

4 Agenda Introduction Basic SQL within a HLL program Processing multiple records Error detection Dynamic SQL Tips and Techniques Summary 7 High Level Languages Supported RPG COBOL C Java AS/400 PL/I FORTRAN/

5 The SQL Precompiler User Source File SQL Precompiler Modified Source File Language Compiler Program Syntax check X-ref host variables SQL statements to calls Comment SQL statements Processed SQL Statements Access Plan 9 SQL Commands Basic commands SELECT - retrieves data; one row or multiple UPDATE - updates one row or multiple DELETE - deletes one row or multiple INSERT - adds one row or multiple Additional functions for complex processing DECLARE CURSOR builds temp result table OPEN and CLOSE open/close result table FETCH row retrieval COMMIT and ROLLBACK journaling functions GRANT and REVOKE security functions 10 5

6 Basic RPG Interface I DS I 1 50 EMPNBR I 6 30 NAM I DEPT SELECT nbr, nam, dpt INTO :empnbr, :nam, :dept FROM emp WHERE nbr = :empnbr Retrieve column/field values into program variables One-to-one correspondence between SELECT list and INTO list SELECT INTO expects only a single row/record Multiple rows require the use of cursor operations 11 Basic Cobol Interface WORKING-STORAGE SECTION. 77 EMPNBR PIC S9(5) COMP DEPT PIC S9(3) COMP NAM PIC X(25).. PROCEDURE DIVISION. EXEC SQL SELECT nbr, nam, dpt INTO :empnbr, :nam, :dept FROM emp WHERE nbr = :empnbr END-EXEC. Retrieve column/field values into program variables One-to-one correspondence between SELECT list and INTO list SELECT INTO expects only a single row/record Multiple rows require the use of cursor operations 12 6

7 Prompting for SQL Use SQL source member types e.g., SQLRPG, SQLRPGLE, SQLCBL, SQLCBLLE Prompting will not work without SQL member type SEU supports prompting today; RSE does not today Both EXEC SQL and END-EXEC statements must be in place Then prompting (F4) will work for statements in between Same prompter as interactive SQL (Start ISQL command) Compile commands OPM compilers CRTSQLRPG, CRTSQLCBL ILE compilers CRTSQLRPGI, CRTSQLCBLI Creates either *PGM, *SRVPGM or *MODULE depending on parameter value specified for "Compile type" or OBJTYPE 13 Prompting Embedded SQL Columns... : 1 71 Edit SKIP/QRPGSRC SEU==> AASQLTST FMT ** *************** Beginning of data ********************** ==>> <<=== Prompt from ==>> SELECT <<=== any of ==>> <<=== these lines ****************** End of data ************************* F3=Exit F4=Prompt F5=Refresh F9=Retrieve F10=Cursor F16=Repeat find F17=Repeat change F24=More keys Any SQL statement can be prompted from within a source program 14 7

8 Prompting for Embedded SQL Specify SELECT Statement Type information for SELECT statement. Press F4 for a list. FROM files SELECT fields..... WHERE conditions.... GROUP BY fields.... HAVING conditions... ORDER BY fields.... FOR UPDATE OF fields.. Type choices, press Enter. emp nbr,_nam,_sal dpt_=_:dept sal Bottom Number of records to optimize DISTINCT records in result file..... N Y=Yes, N=No FOR FETCH ONLY N Y=Yes, N=No UNION with another SELECT N Y=Yes, N=No F3=Exit F4=Prompt F5=Refresh F6=Insert line F9=Subquery F10=Copy F12=Cancel F14=Delete F15=Split line F24=More keys 15 Prompting for Embedded SQL Results of Prompting: Columns... : 1 71 Edit SKIP/QRPGSRC SEU==> AASQLTST FMT ** *************** Beginning of data ********************** SELECT nbr, nam, sal FROM emp WHERE dpt = :dept FOR UPDATE OF sal ****************** End of data ************************* F3=Exit F4=Prompt F5=Refresh F9=Retrieve F10=Cursor F16=Repeat find F17=Repeat change F24=More keys 16 8

9 Embedded SQL in Free Format RPG SQL Statement Start of SQL statement 17 Using Structures in SQL Host structures are groups of variables Data structures in RPG Group items in COBOL Structures can be used in SQL statements Replaces list of variables 18 9

10 Using HLL Structures with SQL RPG COBOL I empds DS I 1 50 EMPNBR I 6 30 NAM I DEPT SELECT nbr, nam, dpt INTO :empds FROM emp WHERE nbr = :empnbr WORKING STORAGE SECTION. 01 EMP_DATA. 05 NBR PIC S9(5) COMP DEPT PIC S9(1) COMP NAME PIC X(25). PROCEDURE DIVISION MOVE 5 TO NBR. EXEC SQL SELECT nbr, pos, nam INTO :EMP_DATA FROM empl WHERE pos=:dept END-EXEC. 19 Agenda Introduction Basic SQL within a HLL program Processing multiple records Error detection Dynamic SQL Tips and Techniques Summary 20 10

11 Selecting and Processing Multiple Rows Steps to access multiple rows: 1 Declare SQL cursor 2 Open cursor 3 Fetch next record 4 Process record (UPDATE/INSERT/etc) 5 If last record: go to Step 6, else: go to Step 3 6 Close cursor 21 Selecting and Processing Multiple Rows DECLARE CURSOR Statement Similar in function to HLL file declarations F-specs or FD's No processing actually takes place - just definition Host variables may be included in the statement Created using an embedded SELECT command most SELECT clauses may be used - ORDER BY, GROUP BY, etc Coded in C-specs of RPG or Procedure Division of COBOL Must be declared before being referenced DECLARE empcsr CURSOR FOR SELECT nbr, nam, sal FROM emp WHERE dpt = :dept 22 11

12 Selecting and Processing Multiple Rows DECLARE CURSOR Statement additional clauses DECLARE empcsr CURSOR FOR SELECT nbr, nam, sal FROM emp WHERE dpt = :dept FOR UPDATE OF sal By default, all columns may be updated or deleted FOR UPDATE OF - lists the columns that are to be updated only columns NOT included in ORDER BY are eligible FOR READ ONLY - specifies no updating/deleting allowed Considerations: FOR READ ONLY - may improve performance; better documentation FOR UPDATE OF - security; may improve performance FOR READ ONLY with insensitive clause 23 Selecting and Processing Multiple Rows DECLARE CURSOR Statement additional clauses DECLARE empcsr CURSOR FOR WITH HOLD SELECT nbr, nam, sal FROM emp WHERE dpt = :dept FOR UPDATE OF sal With Hold clause useful with commitment control Default cursors are closed with commit/rollback commands With Hold keeps cursor open With Hold also an optional clause on the commit/rollback statements 24 12

13 OPEN Statement Executes the SELECT Statement For a Declared Cursor Builds the access path if necessary Successful Open places the file cursor before the first row of the result table Cursor must be closed before it can be opened OPEN empcsr 25 FETCH Statement Two Functions Position the cursor for the next operation FETCH NEXT FROM empcsr Bring rows/records into the program FETCH NEXT FROM empcsr INTO :number, :name, :salary 26 13

14 Selecting and Processing Multiple Rows FETCH Statement Alternatives to Next processing Cursor must be defined as a scrollable Keyword Next Prior First Last Before After Current Relative n Positions Cursor On the next row after the current row On the row before the current row On the first row On the last row Before the first row - must not use INTO After the last row - must not use INTO On the current row (no change in position) n < -1 Positions to nth row before current n = -1 Same as Prior keyword n = 0 Same as Current keyword n = 1 Same as Next keyword n > 1 Positions to nth row after current 27 Selecting and Processing Multiple Rows FETCH Statement Alternatives to Next Processing Cursor must be defined as a scrollable DECLARE empcsr SCROLL CURSOR FOR SELECT nbr, nam, sal FROM emp ORDER BY empid FETCH PRIOR FROM empcsr INTO :number, :name, :salary 28 14

15 Selecting and Processing Multiple Rows Positioned Update and Delete Statements Updates or deletes the current row of an updatable cursor Can only be done after successful Fetch operation "Where Current of" clause in Update and Delete statements DECLARE empcsr CURSOR FOR SELECT nbr, nam, sal FROM emp ORDER BY empid FOR UPDATE OF sal FETCH NEXT FROM empcsr INTO :number, :name, :salary UPDATE emp SET sal = sal + :raise WHERE CURRENT OF empcsr 29 Selecting and Processing Multiple Rows: CLOSE Statement Closes the cursor Cursor must be opened in order to be closed DB2 for i5/os closes cursors for other reasons also: job end activation group ends program ends modules ends commit or rollback without a 'with hold' clause error handling... Rule of thumb - close the cursor when finished with it CLOSE empcsr 30 15

16 Selecting and Processing Multiple Rows Example: Update SALARY for all records in a specified department DECLARE empcsr CURSOR FOR Define SELECT nbr, nam, sal FROM emp WHERE dpt = :dept FOR UPDATE OF sal Load C OPEN empcsr EXFMT PROMPT NOTE: Not all program logic is shown!! 31 Selecting and Processing Multiple Rows Example Continued Retrieve Process Close FETCH NEXT FROM empcsr INTO :number, :name, :salary UPDATE emp SET sal = sal + :raise WHERE CURRENT OF empcsr CLOSE empcsr NOTE: Not all program logic is shown!! 32 16

17 Agenda Introduction Basic SQL within a HLL program Processing multiple records Error detection Dynamic SQL Tips and Techniques Summary 33 Error Detection and Handling Status always returned to HLL code both successful and unsuccessful statements Programmer must check return codes within program SQL Communications Area (SQLCA) contains feedback information must be included in all SQL programs RPG includes SQLCA automatically other languages must have specific include: EXEC SQL END-EXEC INCLUDE SQLCA 34 17

18 Error Detection and Handling SQL Communications Area (SQLCA) SQLCAID Char(8) Structure identifying literal: "SQLCA" SQLCABC Integer Length of SQLCA SQLCode Integer Return code SQLErrML SmallInt Length of SQLErrMC SQLErrMC Char(70) Message Replacement text SQLErrP Char(8) Product ID literal: "QSQ" for DB2/400 SQLErrD Array of Integers SQLErrD(1) - treated as Char(4); last 4 characters of CPF or other escape message SQLErrD(2) - treated as Char(4); last 4 characters of CPF or other diagnostic message SQLErrD(3) - for Fetch, Insert, Update or Delete, number of rows retrieved or updated SQLErrD(4) - for Prepare, relative number indicating resources required for execution SQLErrD(5) - for multiple-row Fetch, contains 100 if last available row is fetched; for Delete, number of rows affected by referential constraints; for Connect or Set Connection, contains t-1 if unconnected, 0 if local and 1 if connection is remote SQLErrD(6) - when SQLCode is 0, contains SQL completion message id 35 Error Detection and Handling SQL Communications Area (SQLCA) - continued SQLWarn Char(11) Set of 11 warning indicators; each is blank, W, or N SQLWarn0 Char(1) Blank if all other SQLWARNx warning indicators are blank W if any warning indicator contains W or N SQLWarn1 Char(1) W if a string column was truncated when assigned to host variable SQLWarn2 Char(1) W if null values were eliminated from a function SQLWarn3 Char(1) W if number of columns is larger than number of host variables SQLWarn4 Char(1) W if prepared Update or Delete statement doesn't include a Where clause SQLWarn5 Char(1) Reserved SQLWarn6 Char(1) W if date arithmetic results in end-of-month adjustment SQLWarn7 Char(1) Reserved SQLWarn8 Char(1) W if result of character conversion contains the substitution character SQLWarn9 Char(1) Reserved SQLWarnA Char(1) Reserved SQLState Char(5) Return code; "00000' if no error or warning 36 18

19 Error Detection and Handling SQLCODE Values SQLCODE (SQLCOD) contains return code = 0 Successful statement execution > 0 Successful, with warning condition < 0 Unsuccessful - statement failed SQLCODE value indicates exact error or condition e.g. 100 = Row not found (or end of file) e.g = Not authorized to object SQLCODE values have corresponding messages e.g. SQL0100 = Row not found e.g. SQL0552 = Not authorized to &1. 37 Error Detection and Handling RPG COBOL SELECT name INTO :nam WHERE emp = 100 C SQLCOD IFLT 0 C EXSR ERR C ENDIF C SQLCOD IFGT 0 C EXSR NF C ENDIF EXEC SQL SELECT name INTO :lastname WHERE emp = 100 END-EXEC. IF SQLCODE < 0 PERFORM ERROR-ROUTINE. ELSE IF SQLCODE > 0 PERFORM NOT-FOUND-ROUTINE ELSE PERFORM GOOD-REC-ROUTINE

20 Error Handling and Detection WHENEVER Statement WHENEVER statement checks SQLCA Can branch to a location based on condition Three conditions: SQLWARNING (SQLCODE > 0 except 100) OR (SQLWARN0 = 'W') SQLERROR (SQLCODE < 0) NOT FOUND (SQLCODE = 100) Two possible actions CONTINUE GO TO label WHENEVER SQLERROR GO TO error 39 Error Detection and Handling Better Way Directly following each SQL statement - code an 'error catcher' Easier to determine source of the error More discrete method of determining action to be taken Example: Update SALARY for all records in a specified department DECLARE empcsr CURSOR FOR Define SELECT nbr, nam, sal FROM emp WHERE dpt = :dept FOR UPDATE OF sal NOTE: Not all program logic is shown!! C EXFMT PROMPT Read operation of EXFMT retrieve dept number 40 20

21 Selecting and Processing Multiple Rows Example Continued Load OPEN empcsr C IF SQLCODE <> 0 C EXSR Err C DOU = 100 FETCH NEXT FROM empcsr INTO :number, :name, :salary Retrieve C IF SQLCODE <> 0 C EXSR Err C DOU = 100 NOTE: Not all program logic is shown!! 41 Selecting and Processing Multiple Rows Example Continued Process Close UPDATE emp SET sal = sal + :raise WHERE CURRENT OF empcsr C IF SQLCODE <> 0 C EXSR Err C ENDIF C ENDIF C ENDDO CLOSE empcsr NOTE: Not all program logic is shown!! 42 21

22 Agenda Introduction Basic SQL within a HLL program Processing multiple records Error detection Dynamic SQL Tips and Techniques Summary 43 Dynamic SQL What is Dynamic SQL? Dynamic SQL is a different way to use SQL SQL statements are not pre-defined in program Dynamically created on the fly as part of program logic SQL pre-compiler cannot fully process dynamically created SQL statements PREPARE statement used in program logic to compile dynamically created SQL statements Can be used with SQL EXECUTE statement 44 22

23 Dynamic SQL What is Dynamic SQL? Offers a high degree of application flexibility Can create/build SQL statement Based on parameters received from Interactive user interface List selection techniques Application control file Use any programming language 45 Dynamic SQL Where to use Dynamic SQL Report programs with user run time selection Files Fields Record selection criteria Sorting SQL built in functions Whenever the exact syntax of an SQL statement cannot be determined beforehand 46 23

24 Dynamic SQL Example 1 User prompted to enter the delete condition (InpCond variable) C Eval SQLStmtStr = 'Delete From Customer C Where ' C Eval SQLStmt = SQLStmtStr + InpCond PREPARE DynSQLStmt FROM :SQLStmt C If (SQLCod = 0) And (SQLWn0 = *Blank) EXECUTE DynSQLStmt 47 Dynamic SQL Example 2: Dynamically select records from the Employee Master File - Any fields, records, or sequence User prompted to enter delete condition (InpCnd) PREPARE search FROM :sqlstm DECLARE empcsr CURSOR FOR search OPEN empcsr 48 24

25 Dynamic SQL Performance considerations Dynamic SQL can be resource intensive Remember that a dynamic SQL statement is parsed (interpreted) and executed within the application program from which it is called May have negative impact on performance Use it... But use it carefully! 49 Agenda Introduction Basic SQL within a HLL program Processing multiple records Error detection Dynamic SQL Tips and Techniques Summary 50 25

26 Performance Tips Embedded SQL Tips Test statements in Interactive SQL before embedding them When exiting Interactive SQL session You can save session statements to a source member Then copy from this member into your program source Default for SQL is to use Commitment Control Requires journaling Program execution fails if updated files are not journaled To request no commitment control COMMIT(*NONE) on compile SQL precompile step happens before RPG/COBOL compile Therefore, if SQL syntax or semantic error occurs, no "typical" compile source listing available Can be very difficult to work through problems at this stage 51 Performance Tips Designing and Writing Efficient SQL Queries SQL uses two basic ways to retrieve data Dataspace scan or arrival sequence Generally used when MORE than 20% of records will be selected Index based or keyed access Generally used when LESS than 20% of records will be selected If SQL can use an index, performance can improve significantly! Create indexes for columns frequently referenced in WHERE clause GROUP BY clause ORDER BY clause Create indexes for fields that are frequently used to join files 52 26

27 Performance Tips Performance Analysis Tools PRTSQLINF Prints information about the embedded SQL statements in a program, SQL package or service program SQL statements Access plans List of command parameters used by precompiler STRDBMON Predictive Query Governor CHGQRYA command TRCJOB Visual Explain (first in V4R5) Operations Navigator 53 Performance Tips Multiple Row FETCH Based on host structure RPG - Multiple Occurence Data Structure COBOL - Occurs clause on declaration of the group item Clause on FETCH FOR n ROWS (n = number of rows to be returned) Specifies number of rows to be retrieved to fill the structure D EMP DS Occurs(10) D NBR 5 0 D NAME 25 D JOB 1 C Z-ADD 5 JOB FETCH Next FROM CustomerCursor FOR 10 ROWS INTO Emp C Eval ErrCond = SQLErrD(5) 54 27

28 Performance Tips Multiple Row FETCH - continued First row fetched- placed into first element of host structure Fetching stops when n rows are returned - or no more records Program variable may be used to specify number of records to be fetched (Note: RPG IV - %Elem built in function) Be Careful - Fetching is always forward from position set by positioning keyword FETCH RELATIVE FOR 3 ROWS is not the same as FETCH PRIOR... FOR 3 ROWS Results: SQLCA updates SQLErrCode(3) to reflect # rows retrieved If no rows returned and no other exceptions, SQLCode is 100 If row(s) returned contains last available row, SQLErrCode(5) set to Performance Tips Blocked INSERT Multiple elements from a host structure are inserted into a table Program variable may be used to set the number of records to be inserted Executes as if n INSERT statements had been issued but with improved performance D EMP DS Occurs(10) D NBR 5 0 D NAME 25 D JOB 1 C/ EXEC SQL INSERT INTO Customer 10 ROWS VALUES :Emp C/ END-EXEC 56 28

29 Other Uses for Embedded SQL Remote Database Access CONNECT TO DISCONNECT RELEASE ALL SET CONNECTION Stored Procedures DECLARE PROCEDURE CALL PROCEDURE INCLUDE statement Dynamic Cursor Query Manager 57 Agenda Introduction Basic SQL within a HLL program Processing multiple records Error detection Dynamic SQL Tips and Techniques Summary 58 29

30 Summary Practical, effective solution for applications requiring complex data retrieval Very flexible, functional tool for development Embedded in a HLL program Entered interactively Portability to other relational databases Easy report writing with programmable flexibility Similarity across many relational databases 59 Bibliography DB2 cross platform web page includes a pointer to a free DB2 Programming FastPath course download SQL/400 Developer s Guide - Paul Conte and Mike Cravitz Database Design and Programming for DB2/400 - Paul Conte S DB2/400: The New AS/400 Database: V3R1 - Skip Marchesani Informational APARs (II09006) IBM Publications on the Web Books 1.ibm.com/servers/eserver/systemi/db2/books.htm White Papers 1.ibm.com/servers/eserver/systemi/db2/db2awp_m.htm Information Centre GO -> Database and file systems -> DB2 for i5/os 60 30

31 Thank You 31