Sql updating multiple rows with different values
The COALESCE function takes a list of parameters, separated by commas, evaluates them and returns the value of the first of its input parameters that is not NULL.
Though COALESCE and ISNULL functions have a similar purpose, they can behave differently.
The usual way to write the update method is as shown below: The issue with this query is that it will take a lot of time as it affects 2 million rows and also locks the table during the update.
You can improve the performance of an update operation by updating the table in smaller groups.
Instead of updating the table in single shot, break it into groups as shown in the above example.
To list the session cursors that each user session currently has opened and parsed, query the dynamic performance view Note: Generally, PL/SQL parses an explicit cursor only the first time the session opens it and parses a SQL statement (creating an implicit cursor) only the first time the statement runs. A SQL statement is reparsed only if it is aged out of the cache by a new SQL statement.
Although you must close an explicit cursor before you can reopen it, PL/SQL need not reparse the associated query.
In Example 6-1, a PL/SQL anonymous block declares three PL/SQL variables and uses them in the static SQL statements DROP TABLE employees_temp; CREATE TABLE employees_temp AS SELECT employee_id, first_name, last_name FROM employees; DECLARE emp_id employees_temp.employee_id%TYPE := 299; emp_first_name employees_temp.first_name%TYPE := 'Bob'; emp_last_name employees_temp.last_name%TYPE := 'Henry'; BEGIN DROP TABLE employees_temp; CREATE TABLE employees_temp AS SELECT employee_id, first_name, last_name FROM employees; DROP TABLE employees_temp2; CREATE TABLE employees_temp2 AS SELECT employee_id, first_name, last_name FROM employees; DECLARE seq_value NUMBER; BEGIN .
You can get information about any session cursor from its attributes (which you can reference in procedural statements, but not in SQL statements).