Scrollable and non-scrollable cursors| When you declare a cursor, you tell DB2 whether you want the cursor to be | scrollable or non-scrollable by including or omitting the SCROLL clause. | This clause determines whether the cursor moves sequentially forward | through the result table or can move randomly through the result table. The simplest type of cursor is a non-scrollable cursor. A non-scrollable | cursor always moves sequentially forward in the result table. When you | open the cursor, the cursor is positioned before the first row in the | result table. When you execute the first FETCH, the cursor is positioned | on the first row. When you execute subsequent FETCH statements, the | cursor moves one row ahead for each FETCH. After each FETCH statement, the | cursor is positioned on the row that you fetched. After you execute a | positioned UPDATE or positioned DELETE operation, the cursor stays at the | current row of the result table. You cannot retrieve rows backward or move | to a specific position in a result table with a non-scrollable cursor.

| To make a cursor scrollable, you declare it as scrollable. To use a | scrollable cursor, you execute FETCH statements that indicate where you | want to position the cursor. | If you want to order the rows of the cursor's result set, and you also | want the cursor to be updatable, you need to declare the cursor as | scrollable, even if you use it only to retrieve rows sequentially. You can | use the ORDER BY clause in the declaration of an updatable cursor only if | you declare the cursor as scrollable. | Declaring a scrollable cursor: To indicate that a cursor is scrollable, | you declare it with the SCROLL keyword. The following examples show a | characteristic of scrollable cursors: the sensitivity. | EXEC SQL DECLARE C1 INSENSITIVE SCROLL CURSOR FOR | SELECT DEPTNO, DEPTNAME, MGRNO | FROM DSN8710.DEPT | ORDER BY DEPTNO | END-EXEC.| Declaring a scrollable cursor with the INSENSITIVE keyword has the | following effects: | The size, the order of the rows, and the values for each row of the | result table do not change after you open the cursor. | The result table is read-only. Therefore, you cannot declare the | cursor with the FOR UPDATE clause, and you cannot use the cursor for | positioned update or delete operations. | EXEC SQL DECLARE C2 SENSITIVE STATIC SCROLL CURSOR FOR | SELECT DEPTNO, DEPTNAME, MGRNO | FROM DSN8710.DEPT | ORDER BY DEPTNO | END-EXEC.

| Declaring a cursor as SENSITIVE has the following effects: | When you execute positioned UPDATE and DELETE statements with the | cursor, those updates are visible in the result table. | When the current value of a row no longer satisfies the SELECT | statement for the cursor, that row is no longer visible in the result | table. | When a row of the result table is deleted from the underlying table, | the row is no longer visible in the result table. | Changes that are made to the underlying table by other cursors or | other application processes can be visible in the result table, | depending on whether the FETCH statements that you use with the cursor | are FETCH INSENSITIVE or FETCH SENSITIVE statements.

| In DB2 Version 7, when you declare a cursor as SENSITIVE, you must also | declare it as STATIC. Declaring the cursor as STATIC has the following | effects: | The size of the result table does not grow after you open the cursor. | Rows that are inserted into the underlying table are not added to the | result table. | The order of the rows does not change after you open the cursor. | If the cursor declaration contains an ORDER BY clause, and columns | that are in the ORDER BY clause are updated after you open the cursor, | the order of rows in the result table does not change. |Table4.Positionsforascrollablecursor

||KeywordinFETCHstatement|CursorpositionwhentheFETCHis|executed

|BEFORE|Beforethefirstrow

|FIRSTorABSOLUTE+1|Atthefirstrow

|LASTorABSOLUTE-1|Atthelastrow

|AFTER|Afterthelastrow

|ABSOLUTE(1)|||Toanabsoluterownumber,from|beforethefirstrowforwardorfrom|afterthelastrowbackward

|RELATIVE(1)||Forwardorbackwardarelativenumber|ofrows

|CURRENT|Atthecurrentrow

|PRIORorRELATIVE-1|Tothepreviousrow

|NEXTorRELATIVE+1|Tothenextrow(default)

The following examples show the SQL statements that you must include in a COBOL program to define and use a cursor. Figure 16 shows how to use a non-scrollable cursor to perform FETCH and positioned UPDATE operations.

************************************************** * Declare a cursor that will be used to update * * the JOB and WORKDEPT columns of the EMP table. * ************************************************** EXEC SQL DECLARE THISEMP CURSOR FOR SELECT EMPNO, LASTNAME, WORKDEPT, JOB FROM DSN8710.EMP WHERE WORKDEPT = 'D11' FOR UPDATE OF JOB END-EXEC. ************************************************** * Open the cursor * ************************************************** EXEC SQL OPEN THISEMP END-EXEC. ************************************************** * Indicate what action to take when all rows * * in the result table have been fetched. * ************************************************** EXEC SQL WHENEVER NOT FOUND GO TO CLOSE-THISEMP END-EXEC. ************************************************** * Fetch a row to position the cursor. * ************************************************** EXEC SQL FETCH THISEMP INTO :EMP-NUM, :NAME2, :DEPT, :JOB-NAME END-EXEC. ************************************************** * Update the row that the cursor points to. * ************************************************** EXEC SQL UPDATE DSN8710.EMP SET JOB = :NEW-JOB WHERE CURRENT OF THISEMP END-EXEC. ************************************************** * Branch back to fetch and process the next row. * ************************************************** . . . ************************************************** * Close the cursor * ************************************************** CLOSE-THISEMP. EXEC SQL CLOSE THISEMP END-EXEC.

Figure 16. Performing cursor operations with a non-scrollable cursor

Figure 17 shows how to use a scrollable cursor to retrieve data backward from a table.

************************************************** * Declare a cursor that will be used to retrieve * * the data backward from the EMP table. The * * cursor should have access to changes by other * * processes. * ************************************************** EXEC SQL DECLARE THISEMP SENSITIVE STATIC SCROLL CURSOR FOR SELECT EMPNO, LASTNAME, WORKDEPT, JOB FROM DSN8710.EMP END-EXEC. ************************************************** * Open the cursor * ************************************************** EXEC SQL OPEN THISEMP END-EXEC. ************************************************** * Indicate what action to take when all rows * * in the result table have been fetched. * ************************************************** EXEC SQL WHENEVER NOT FOUND GO TO CLOSE-THISEMP END-EXEC. ************************************************** * Position the cursor after the last row of the * * result table. This FETCH statement cannot * * include the SENSITIVE or INSENSITIVE keyword * * and cannot contain an INTO clause. * ************************************************** EXEC SQL FETCH AFTER THISEMP END-EXEC. ************************************************** * Fetch the previous row in the table. * ************************************************** EXEC SQL FETCH SENSITIVE PRIOR THISEMP INTO :EMP-NUM, :NAME2, :DEPT, :JOB-NAME END-EXEC. ************************************************** * Check that the fetched row is not a hole * * (SQLCODE +222). If the row is not a * * hole, print the row contents. * ************************************************** IF SQLCODE IS GREATER THAN OR EQUAL TO 0 AND SQLCODE IS NOT EQUAL TO +100 AND SQLCODE IS NOT EQUAL TO +222 THEN PERFORM PRINT-RESULTS. ************************************************** * Branch back to fetch the previous row. * ************************************************** . . . ************************************************** * Close the cursor * ************************************************** CLOSE-THISEMP. EXEC SQL CLOSE THISEMP END-EXEC.

Describing the access path of a database fileAn access path describes the order in which records are to be retrieved. When youdescribe an access path, you describe whether it will be a keyed sequence orarrival sequence access path.

The DDS for a physical file must be in the following order File level entries (optional). The UNIQUE keyword is used to indicate thatthe value of the key field in each record in the file must be unique.Duplicate key values are not allowed in this file.Record format level entries. The record format name is specified, alongwith an optional text descriptionField level entries. The field names and field lengths are specified, alongwith an optional text description for each field.Key field level entries (optional). The field names used as key fields arespecified.Comment (optional).

The data type is specified in position 35. The valid data types are:Entry MeaningA CharacterPPacked decimalSZoned decimalBBinaryFFloating pointHHexadecimalLDateTTimeZTimestamp

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PROCEDURE DIVISION. 120 121 A000-MAIN. 122 MOVE 1.04 TO PERCENTAGE. 123 OPEN OUTPUT PRINTFILE. 124 125 *************************************************************** 126 * Update the selected employees by the new percentage. If an * 127 * error occurs during the update, ROLLBACK the changes, * 128 *************************************************************** 129 130 3 EXEC SQL 131 WHENEVER SQLERROR GO TO E010-UPDATE-ERROR 132 END-EXEC. 133 4 EXEC SQL 134 UPDATE CORPDATA/EMPLOYEE 135 SET SALARY = SALARY * :PERCENTAGE 136 WHERE COMM >= :COMMISSION 137 END-EXEC. 138 139 *************************************************************** 140 * Commit changes. * 141 *************************************************************** 142 143 5 EXEC SQL 144 COMMIT 145 END-EXEC. 146 147 EXEC SQL 148 WHENEVER SQLERROR GO TO E020-REPORT-ERROR 149 END-EXEC. 150 151 *************************************************************** 152 * Report the updated statistics for each employee receiving * 153 * a raise and the projects that s/he participates in * 154 *************************************************************** 155 156 *************************************************************** 157 * Write out the header for Report 1. * 158 *************************************************************** 159 160 write print-record from rpt1-header1 161 before advancing 2 lines. 162 write print-record from rpt1-header2 163 before advancing 1 line. 164 6 exec sql 165 declare c1 cursor for 166 SELECT DISTINCT projno, empprojact.empno, 167 lastname||", "||firstnme ,salary 168 from corpdata/empprojact, corpdata/employee 169 where empprojact.empno =employee.empno and 170 comm >= :commission 171 order by projno, empno 172 end-exec. 173 7 EXEC SQL 174 OPEN C1 175 END-EXEC. 176 177 PERFORM B000-GENERATE-REPORT1 THRU B010-GENERATE-REPORT1 EXIT 178 UNTIL SQLCODE NOT EQUAL TO ZERO. 180 10 A100-DONE1. 181 EXEC SQL 182 CLOSE C1 183 END-EXEC.

TriggersA trigger is a set of actions that runs automatically when a specified change operation is performed on a specified table or view. The change operation can be an SQL INSERT, UPDATE, or DELETE statement, or an insert, an update, or a delete high-level language statement in an application program. Triggers are useful for tasks such as enforcing business rules, validating input data, and keeping an audit trail.Triggers can be defined as SQL or external.For an external trigger, the CRTPFTRG CL command is used. The program containing the set of trigger actions can be defined in any supported high level language. External triggers can be insert, update, delete, or read triggers.For an SQL trigger, the CREATE TRIGGER statement is used. The trigger program is defined entirely using SQL. SQL triggers can be insert, update, or delete triggers.Once a trigger is associated with a table or view, the trigger support calls the trigger program whenever a change operation is initiated against the table or view, or any logical file or view created over the table or view. SQL triggers and external triggers can be defined for the same table. Only SQL triggers can be defined for a view. Up to 200 triggers can be defined for a single table or view.Each change operation for a table can call a trigger before or after the change operation occurs. Additionally, you can add a read trigger that is called every time the table is accessed. Thus, a table can be associated with many types of triggers. Before delete trigger Before insert trigger Before update trigger After delete trigger After insert trigger After update trigger Read-only trigger (external trigger only)Each change operation for a view can call an instead of trigger which will perform some set of actions instead of the insert, update, or delete. A view can be associated with an: Instead of delete trigger Instead of insert trigger Instead of update triggerSQL triggersThe SQL CREATE TRIGGER statement provides a way for the database management system to actively control, monitor, and manage a group of tables and views whenever an insert, an update, or a delete operation is performed.The statements specified in the SQL trigger are executed each time an SQL insert, update, or delete operation is performed. An SQL trigger may call stored procedures or user-defined functions to perform additional processing when the trigger is executed.Unlike stored procedures, an SQL trigger cannot be directly called from an application. Instead, an SQL trigger is invoked by the database management system on the execution of a triggering insert, update, or delete operation. The definition of the SQL trigger is stored in the database management system and is invoked by the database management system when the SQL table or view that the trigger is defined on, is modified.An SQL trigger can be created by specifying the CREATE TRIGGER SQL statement. All objects referred to in the CREATE TRIGGER statement (such as tables and functions) must exist; otherwise, the trigger will not be created. The statements in the routine-body of the SQL trigger are transformed by SQL into a program (*PGM) object. The program is created in the schema specified by the trigger name qualifier. The specified trigger is registered in the SYSTRIGGERS, SYSTRIGDEP, SYSTRIGCOL, and SYSTRIGUPD SQL catalogs.External triggersFor an external trigger, the program that contains the set of trigger actions can be defined in any supported high-level language that creates a *PGM object.The trigger program can have SQL embedded in it. To define an external trigger, you must create a trigger program and add it to a table using the ADDPFTRG CL command or you can add it using iSeries Navigator. To add a trigger to a table, you must: Identify the table Identify the kind of operation Identify the program that performs the actions that you want.http://publib.boulder.ibm.com/html/as400/v4r5/ic2979/info/db2/rbafomstrzahftri.htmIn this section, we focus on the OCCURS clause to store table data. As we will see, tables and arrays are stored in exactly the same way; they are, however, used for different purposes. A table is a list of stored fields that are looked up or referenced by the pro-gram. Tables are used in conjunction with table look-ups, whereas a table look-up is a procedure that finds a specific entry in the table. Thus, an array stores data or totals to be manipulated or outputted, whereas a table is used for looking up, or referencing, data.Array can be declared in cobol using the OCCURS clause.For one dimensional array,

01 Arrays.05 Var1 PIC X(10) Occurs 10 times.

For two dimensional array,

01 Arrays.03 AAA Occurs 10 times05 BBB Occurs 10 times07 Value PIC 9(3).01 ARRAYNAME05 ARRAY-RECDFORMAT OCCURS 20 TIMES10 ARRAYNAME-FIELDNAME1 PIC X(20)10 ARRAYNAME-FIELDNAME2 PIC X(30)

AND WE CAN ACCESS THIS ARRAY BY USING SUBSCRIPT...LIKE DISPLAY ARRAY-NAME(I)AND ALSO INDIVIDUAL FIELD: DISPLAY ARRAYNAME-FIELD1(I)1. What are the different levels available in COBOL?Level Numbers available are 01-49, 66, 77, 8801-49Group or elementary items66Renames clause77Independent elementary data itemsused for LIKE Clausecannot have an OCCURS clause.88Condition names 2. What is 77 level used for?Elementary level item. Cannot be subdivisions of other items (cannot be qualified), nor can they be subdivided themselves. 3. What is 88 level used for?88 level is used for condition names.The level 88 in the Data Division can be used to give condition names to the values that a field contains. A condition name entry specifies either a single value or a set of values for the condityional variable. When this level is specified you can use the condition name instead of is =equal to in the IF statement. Condition name should be specified under Level 88 immediately following the field description.

Example:01 WS-MARITAL-STATUS PIC X.88 SINGLE VALUE Y.88 MARRIED VALUE N.01 WS-REPLY PIC X.88 REPLY-YESVALUE Y.88 REPLY-N0VALUE N. 01 WS-MARKS PIC 999.88 PASSED VALUE 40 THRU 100.88 FAILED VALUE 0 THRU 39. 4. What are level 66 used for?For RENAMES clause. 5. What is the difference between level 77 and 01? And which is more efficient? Level 77 can be used to describe independent elementary items in the Working Storage or Linkage Sections. Level 77 cannot use Redefines.

Level 01 can be used to describe both elementary and group items. Any item described in Level 01, the system is putting on Double-Word boundary and inserts slack bytes if necessary 6. How many different level numbers can be used in COBOL to describe a record? 01-49. 7. Give some advantages of REDEFINES clause.1.You can REDEFINE a Variable from one PI1CTURE class to another PICTURE class by using the same memory location. Multiple REDEFINES of same area possible2. By REDEFINES we can INITIALISE the variable in WORKING-STORAGE Section itself.3. We can REDEFINE a Single Variable into so many sub-variables. Syntax: REDEFINES

Example:

01 Sales-Record.02 Sales-TypePic X.02 Sales-By-Unit.03 QtyPic 9(4).03 Unit-PricePic 9(8)V99.02 Total-Sales REDEFINES Sales-By-Unit.03 AmountPic 9(10)V99.03 Filler Pic X(2).

8. Can I redefine an X (100) field with a field of X (200)?Yes.

Redefines just cause both fields to start at the same location. For example:01 WS-TOP PIC X (1)01 WS-TOP-RED REDEFINES WS-TOP PIC X (2).

If you MOVE 12 to WS-TOP-RED, DISPLAY WS-TOP will show 1 while DISPLAY WS-TOP-RED will show 12.

9. Can I redefine an X (200) field with a field of X (100)?Yes.

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http://www-01.ibm.com/support/docview.wss?uid=nas8N1010265 expandable, Loading One Page at a Timehttp://www-01.ibm.com/support/docview.wss?uid=nas8N1010285 msg subfilehttp://www.ibm.com/Search/?q=single+page+subfile+in+cobol&v=17&en=utf&lang=en&cc=us very imp linkhttp://search400.techtarget.com/answer/Whats-the-difference-between-the-three-types-of-subfiles-as-in-the-DDSThe hierarchy consists of Divisions, Sections, Paragraphs, Sentences and Statements. A Division may contain one or more Sections, a Section one or more Paragraphs, a Paragraph one or more Sentences and a Sentence one or more Statements. A statement consists of a COBOL verb and an operand or operands.For basic cobolhttp://www.mainframegurukul.com/tutorials/programming/cobol/cobol-data-items.htmlhttp://www.mainframegurukul.com/tutorials/programming/cobol/cobol-tutorial.html