Updating two different tables with cursor oracle Hidden adult webcams


24-Jul-2017 15:57

The Oracle bulk collect tells the SQL engine to fetch multiple rows at once and store them in a collection defined by the developer. Now we can turn that query into a PL/SQL cursor, process the results in bulk, and perform the required update using a FORALL statement.With the addition of the use of the FORALL statement, this greatly reduces the amount of context switching between PL/SQL and SQL by sending DML statements from PL/SQL to SQL in batches rather than one at a time, resulting in dramatic performance improvements over row-by-row processing. Incidentally, the above query returns 999,000 rows.Consider the following two tables: You have been tasked with updating the employee salaries in the EMPLOYEES table with the maximum salary for the same employee, based on EMPLOYEE_ID, in the NEW_SALARY_INFO table. There is no index on the NEW_SALARY_INFO table so the database will have to full scan a four million row table for each of the one million employee records to find the maximum salary.If no record exists in the NEW_SALARY_INFO table for an employee, that employee’s data should remain the same. We’ll just use an UPDATE statement to modify the rows in the EMPLOYEES table: UPDATE employees e SET employee_salary = ( SELECT MAX(salary) FROM new_salary_info nsi WHERE nsi.employee_id = e.employee_id ) WHERE EXISTS ( SELECT NULL FROM new_salary_info nsi2 WHERE nsi2.employee_id = e.employee_id ); PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes |Temp Spc| Cost (%CPU)| Time | -------------------------------------------------------------------------------------------- | 0 | UPDATE STATEMENT | | 999K| 17M| | 2772M (2)| 9| | 1 | UPDATE | EMPLOYEES | | | | | | |* 2 | HASH JOIN SEMI | | 999K| 17M| 23M| 7887 (1)| | | 3 | TABLE ACCESS FULL| EMPLOYEES | 1000K| 12M| | 690 (2)| | | 4 | TABLE ACCESS FULL| NEW_SALARY_INFO| 3996K| 19M| | 2764 (2)| | | 5 | SORT AGGREGATE | | 1 | 13 | | | | |* 6 | TABLE ACCESS FULL| NEW_SALARY_INFO| 4 | 52 | | 2772 (2)| | -------------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - access("NSI2"."EMPLOYEE_ID"="E"."EMPLOYEE_ID") 6 - filter("NSI"."EMPLOYEE_ID"=: B1) Hmm, that doesn’t look very promising at all. Well, SQL is pretty awesome, so there must be another way to do this. UPDATE ( SELECT e.employee_id, e.employee_salary, NVL(( SELECT MAX(nsi.salary) FROM new_salary_info nsi WHERE e.employee_id = nsi.employee_id ), e.employee_salary) AS new_sal FROM employees e ) SET employee_salary = new_sal; PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ------------------------------------------------------------------------------------- | 0 | UPDATE STATEMENT | | 1000K| 12M| 2772M (2)|9 | | 1 | UPDATE | EMPLOYEES | | | | | | | 2 | TABLE ACCESS FULL | EMPLOYEES | 1000K| 12M| 690 (2)| | | 3 | SORT AGGREGATE | | 1 | 13 | | | |* 4 | TABLE ACCESS FULL| NEW_SALARY_INFO | 4 | 52 | 2772 (2)| | ------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 4 - filter("NSI"."EMPLOYEE_ID"=: B1)MERGE INTO employees e USING ( SELECT e.rowid AS e_rowid, MAX(nsi.salary) AS new_sal FROM employees e, new_salary_info nsi WHERE e.employee_id = nsi.employee_id GROUP BY e.rowid ) new_salaries ON (e.rowid = new_salaries.e_rowid) WHEN MATCHED THEN UPDATE SET e.employee_salary = new_salaries.new_sal; Curses! It turns out there is a VPD security policy on the EMPLOYEES table that prevents us from using the MERGE. All of our attempts at using SQL have been stymied. By making use of bulk processing in PL/SQL we can perform our task rather quickly and with minimal code.

Continue Reading → PL/SQL and SQL both are incredibly powerful languages that allow us to do some pretty amazing things with data.By using the same mechanics, a SQL procedure can also define a result set and return it directly to the caller of the SQL procedure or to a client application.A cursor can be viewed as a pointer to one row in a set of rows.You can also perform more complicated updates in Oracle.

updating two different tables with cursor oracle-61

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You may wish to update records in one table based on values in another table.COUNT 25 UPDATE employees 26 SET employee_salary = lt_new_salary_info(i).new_salary 27 WHERE employee_id = lt_new_salary_info(i).employee_id; 28 29 v_rowcount := v_rowcount SQL%ROWCOUNT; 30 END LOOP; 31 32 CLOSE c_new_salary_info; 33 34 DBMS_OUTPUT. The first reason has already been noted, and that is the use of bulk operations and FORALL to reduce context switching between PL/SQL and SQL. The optimizer no longer has to worry about performing an update as part of the query and is able to simply join the two tables in a very efficient manner.