A PL/pgSQL cursor
allows you to encapsulate a query and process each individual row at a time
. Typically, you use cursors when you want to divide a large result set into parts and process each part individually. If you process it at once, you may have a memory overflow error.
How does Postgres cursor work?
When CURSOR is declared with a select statement,
DB will execute the
select statement and then have the result stored in DB memory. When FETCH is called on the CURSOR , DB will just read the result moving on the CURSOR . When the CURSOR is closed, results stored is removed from memory.
What is a cursor Plsql?
A cursor is
a pointer to this context area
. … PL/SQL controls the context area through a cursor. A cursor holds the rows (one or more) returned by a SQL statement. The set of rows the cursor holds is referred to as the active set.
What are the steps for using a cursor?
- DECLARE the cursor in the Declaration section.
- OPEN the cursor in the Execution Section.
- FETCH the data from the cursor into PL/SQL variables or records in the Execution Section.
- CLOSE the cursor in the Execution Section before you end the PL/SQL Block.
What do you mean by cursor explain its types?
Cursor is a Temporary Memory or Temporary Work Station. It is Allocated by Database Server at the Time of Performing DML operations on Table by User. Cursors are used to store Database Tables. There are 2 types of Cursors:
Implicit Cursors, and Explicit Cursors
. These are explained as following below.
When should indexes be avoided?
Indexes should
not be used on small tables
. Tables that have frequent, large batch updates or insert operations. Indexes should not be used on columns that contain a high number of NULL values. Columns that are frequently manipulated should not be indexed.
What is the syntax for opening a unbounded cursor?
OPEN unbound_cursorvar [ [ NO ] SCROLL ]
FOR query; The cursor variable is opened and given the specified query to execute. The cursor cannot be open already, and it must have been declared as an unbound cursor variable (that is, as a simple refcursor variable).
Can we declare cursor inside begin?
In general,
yes you can
, you just nest another execution block inside your current one…
What can a cursor FOR loop use?
The cursor FOR LOOP statement implicitly declares its loop index as a record variable of the row type that a specified cursor returns, and then opens a cursor. With each iteration, the cursor FOR LOOP statement fetches a row from the result set into the record.
Which type of cursor is automatically declared?
21) Which type of cursor is automatically declared by Oracle every time an SQL statement is executed? Explanation:
The implicit cursor
are automatically created.
What is the use of cursor explain with example in Android?
A Cursor represents
the result of a query and basically points to one row of the query result
. This way Android can buffer the query results efficiently; as it does not have to load all data into memory. To get the number of elements of the resulting query use the getCount() method.
What is the difference between cursor and select statement?
Opening the cursor
To open a cursor, it is required to declare it first. It is declared using the DATA statement and special data type CURSOR. All clauses of SELECT statement can be used except the INTO clause. After the OPEN CURSOR statement, the database cursor points to the first line of the result set.
How do I open a cursor in SQL?
- Declare a cursor that defines a result set.
- Open the cursor to establish the result set.
- Fetch the data into local variables as needed from the cursor, one row at a time.
- Close the cursor when done.
Which one best describes why cursor is used?
Cursors are used by
database programmers to process individual rows returned by database system queries
. Cursors enable manipulation of whole result sets at once. In this scenario, a cursor enables the sequential processing of rows in a result set.
What is cursor life cycle?
SQL Cursor Life Cycle
A
cursor is opened for storing data retrieved from the result set
. Fetching Cursor. When a cursor is opened, rows can be fetched from the cursor one by one or in a block to do data manipulation. Closing Cursor. The cursor should be closed explicitly after data manipulation.
What is cursor status?
An application uses the cursor status property
to determine how a cancel operation has affected a cursor
. CS_CUR_STATUS is a command structure property and cannot be retrieved at the connection or context levels. Cursor properties are useful to gateway applications that send cursor information to clients.
