That allows us to perform operations on every record on a one-by-one basis.
You use the CREATE TABLE employees_temp AS SELECT employee_id, first_name FROM employees; CREATE TABLE employees_temp2 AS SELECT employee_id, first_name FROM employees; DECLARE next_value NUMBER; BEGIN -- The NEXTVAL value is the same no matter what table you select from. NEXTVAL INTO next_value FROM dual; -- You usually use NEXTVAL to create unique numbers when inserting data. NEXTVAL, 'value 1'); -- If you need to store the same value somewhere else, you use CURRVAL. CURRVAL, 'value 1'); -- Because NEXTVAL values might be referenced by different users and -- applications, and some NEXTVAL values might not be stored in the -- database, there might be gaps in the sequence.
END; / DROP TABLE employees_temp; DROP TABLE employees_temp2; statement to organize rows from a database table into a tree structure.
There can be a situation where you have to use a cursor, even though the experts say not to use cursors or to avoid them as much as possible.
But if you look closely, most of the time we use cursors to iterate through a row collection and update the same table.
In these type of situations, it is ideal to use a Update Cursor, than using the default read only one.
Consider the following table: Here is how you use the Update Cursor.Cursor declarations must appear after variable and condition declarations but before handler declarations.Also keep in mind that the cursor SELECT statement cannot have an INTO clause; it's strictly read-only.It’s important to know when not to use cursor FOR loops.My mentor told me that when querying data I should always use a cursor FOR loop, even for a single row lookup. It’s great to learn from others, and it’s especially wonderful when the lesson you learn is simple and easy to remember.He says it’s the easiest way to fetch data, and Oracle Database automatically optimizes it in Oracle Database 10g and above. It’s not so great, however, when the advice is simplistic and results in suboptimal code.