Updating a record using cursor
You use three commands to control a cursor: You must declare a cursor before referencing it in other statements.
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.
clause specifying the PL/SQL variable to hold the result: If the query might return more than one row, but you do not care about values after the first, you can restrict any result set to a single row by comparing the value: If the query might return no rows at all, use an exception handler to specify any actions to take when no data is found: If you just want to check whether a condition exists in your data, you might be able to code the query with the record whose field names match the column names from the query, and that exists only during the loop.
When you use expressions rather than explicit column names, use column aliases so that you can refer to the corresponding values inside the loop: clauses, depending on the situation.
You might use sequence numbers to give each row a unique identifier, and refer to those identifiers from other rows to set up parent-child relationships.