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Database Articles
Page 216 of 547
What is the usage of host variables in case of multi row fetch?
The host variable needs to be declared as an array for the multi-row fetch. Also, we need to define another variable in the working storage section with the configuration S9(4) COMP, which will store the value of the number of rows to be fetched in a single fetch call.We can give any name to this variable, here we have used MAX-ROW. Below is an example of declaring a host variable array and MAX-ROW.01 ORDER-ID PIC X(25) OCCURS 25 TIMES. 01 MAX-ROW PIC S9(4) COMP VALUE 25.We will fetch the cursor like below.EXEC SQL FETCH NEXT ROWSET FROM ORDER_CUR FOR ...
Read MoreHow will you extract multiple rows from a DB2 table in a single FETCH call?
We can extract multiple rows from a DB2 table in a single FETCH call using a concept of multi row fetch.In a multi row fetch, we have to declare the cursor with the clause “WITH ROWSET POSITIONING”. The host variable in this case should be declared as an array.Therefore, in a single fetch statement the host variable array will be populated with the multiple row data. We can traverse in the host variable array in order to access this row data.For example, we can declare a multi fetch cursor like below−EXEC SQL DECLARE ORDER_CUR WITH ROWSET POSITIONING FOR ...
Read MoreHow to fetch data from an unopened cursor or opening an already opened cursor?
When we try to fetch the data from the CURSOR which is not open the query will fail. In this case the SQLCODE field of SQLCA will be populated with the DB2 error code - 501. As per the IBM documentation -501 error code states that−“THE CURSOR IDENTIFIED IN A FETCH OR CLOSE STATEMENT IS NOT OPEN”When we try to OPEN the cursor which is already open then the query will fail and we will get the error code as -502 in the SQLCODE field of SQLCA. As per the IBM documentation -502 error code states that−“THE CURSOR IDENTIFIED IN ...
Read MoreIs it possible to update a CURSOR in which we have used JOIN on 2 tables ORDERS and TRANSACTIONS? Why or Why not? How can we proceed to UPDATE any of these tables?
When we use JOIN on one (self join) or more table inside a cursor declaration then a read-only cursor will be created. We cannot update the read-only cursor.If we want to update any of the tables used in the JOIN then we have to declare a separate cursor for all the tables and an individual logic has to be built in order to update each DB2 table.
Read MoreHow will you keep the CURSOR open after firing COMMIT in a COBOL-DB2 program?
Whenever we issue a COMMIT statement, all the open cursors will get closed. This is a very common case when we have to frequently use the commit statement after a UPDATE while working with a cursor. In this case we can use the “WITH HOLD” clause during the cursor declaration.The “WITH HOLD” clause will keep the cursor open even after firing the COMMIT statement. We can give the “WITH HOLD” clause in the following way.EXEC SQL DECLARE ORDER_CUR CURSOR WITH HOLD FOR SELECT ORDER_ID, TRANSACTION_ID FROM ORDERS WHERE ORDER_DATE = ‘2020-07-28’ END-EXEC
Read MoreWhat is the purpose and usage of "WHERE CURRENT OF" clause in a COBOL-DB2 program?
The “WHERE CURRENT OF” clause will place the exclusive lock on the row once the UPDATE statement is executed. The “WHERE CURRENT OF” clause will point to the most recently fetched row of the cursor.We can update the rows in cursor using “WHERE CURRENT OF” in the following way.CURSOR definition.EXEC SQL DECLARE ORDER_CUR CURSOR FOR SELECT ORDER_ID, TRANSACTION_ID FROM ORDERS WHERE ORDER_DATE = ‘2020-07-28’ END-EXECOPEN cursorEXEC SQL OPEN ORDER_CUR END-EXECFETCH cursor and Update rowSET WF-END-CURSOR-N TO TRUE PERFORM UNTIL WF-END-CURSOR-Y EXEC SQL FETCH ORDER_CUR INTO :ORDER-ID, :TRANSACTION-ID END-EXEC IF TRANSACTION-ID NOT = SPACES EXEC SQL ...
Read MoreWhat are the steps involved to use a CURSOR in any COBOL-DB2 program?
The CURSOR is used when we have to fetch multiple rows from a table. There are 4 steps involved in order to use a cursor in a COBOL-DB2 program.DECLARE cursor− In this step we will define the layout of the cursor. We will give the query we want to use. For example−EXEC SQL DECLARE ORDER_CUR CURSOR FOR SELECT ORDER_ID FROM ORDERS WHERE ORDER_DATE = ‘2020-07-28’ END-EXECOPEN cursor− Next we will open our cursor. This statement readies the cursor for data retrieval. For example−EXEC SQL OPEN ORDER_CUR END-EXECFETCH cursor− In this statement, we start fetching the data from DB2 and the ...
Read MoreExplain the scenario in which CURSOR should be used over a standalone SELECT statement?
The standalone SELECT statement is generally used when we use a primary or an alternate key in the WHERE clause. Therefore, In this case we are certain that the standalone select statement will return only one row since the primary key cannot have a duplicate value (multiple rows).If we want to query the database using a non-unique key which could return multiple rows from a DB2 table, we have to use a cursor to handle the multiple rows returned. We can access the cursor in a loop to read each row data one by one.For example, if we want to ...
Read MoreWhat we can conclude if the final value in the NULL indicator is -2?
A NULL indicator is a 2 bytes field which serves the multiple purpose. This indicator takes the value as -1 when any DB2 column has NULL value and it takes the value as 0 when DB2 column has a non NULL value.Although the main purpose of the NULL indicator is to check whether a column has a NULL value or not, this indicator can take a value of -2 as well. A -2 value in this indicator states that a NULL value was assigned to the host variable as a result of evaluating an expression with an arithmetic error, or ...
Read MoreWhat is the purpose of "NOT NULL WITH DEFAULT" clause used in DB2 table column?
When we define the DB2 table, we can declare any column as “NOT NULL” which means that in any case this column cannot store NULL value.Now if we try to store a NULL value in this column in our COBOL-DB2 program using -1 value in the NULL indicator then our query will fail. In this case the SQLCODE field of SQLCA will give the error code as -407. As per the IBM documentation -407 error code states that−“AN UPDATE, INSERT, OR SET VALUE IS NULL, BUT THE OBJECT COLUMN CANNOT CONTAIN NULL VALUES”.
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