Difference Between Cursor And Ref Cursor In Oracle Pl Sql Tutorial Pdf
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This does not apply to a BULK or multirow operation. Oracle is transaction oriented; that is, Oracle uses transactions to ensure data integrity. A transaction is a series of SQL data manipulation statements that does a logical unit of work.
It is important not to allow one operation to succeed while the other fails. At the end of a transaction that makes database changes, Oracle makes all the changes permanent or undoes them all.
If your program fails in the middle of a transaction, Oracle detects the error and rolls back the transaction, restoring the database to its former state. Example shows some queries that call SQL functions. However, there are limitations on the use of pseudocolumns, including the restriction on the use of some pseudocolumns in assignments or conditional tests.
A sequence is a schema object that generates sequential numbers. When you create a sequence, you can specify its initial value and an increment. To get the current or next value in a sequence, use dot notation:. Each time you reference the NEXTVAL value of a sequence, the sequence is incremented immediately and permanently, whether you commit or roll back the transaction.
After creating a sequence, you can use it to generate unique sequence numbers for transaction processing. Example shows how to generate a new sequence number and refer to that same number in more than one statement.
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. LEVEL returns the level number of a node in a tree structure. The root is level 1, children of the root are level 2, grandchildren are level 3, and so on. You specify the direction in which the query traverses the tree down from the root or up from the branches with the PRIOR operator.
ROWID returns the rowid binary address of a row in a database table. For an example, see "Fetching Across Commits". This section briefly describes some of these operators. You can use the comparison operators in the following list to form predicates. Set operators combine the results of two queries into one result. MINUS returns all distinct rows selected by the first query but not by the second.
UNION returns all distinct rows selected by either query. Row operators return or reference particular rows. ALL retains duplicate rows in the result of a query or in an aggregate expression.
PRIOR refers to the parent row of the current row returned by a tree-structured query. You must declare an explicit cursor for queries that return more than one row.
However, you can track information about the execution of an implicit cursor through its cursor attributes. The values of the cursor attributes always refer to the most recently executed SQL statement. To save an attribute value for later use, assign it to a local variable immediately. The following are considerations when using attributes of implicit cursors:.
The values of the cursor attributes always refer to the most recently executed SQL statement, wherever that statement is.
It might be in a different scope for example, in a sub-block. Doing other operations, such as procedure calls, might change the value of the variable before you can test it. First, you initialize the cursor with the OPEN statement, which identifies the result set. This technique requires more code than other techniques such as the implicit cursor FOR loop. Its advantage is flexibility. You can:. Process multiple rows in a single loop iteration, skip rows, or split the processing into more than one loop.
You must declare a cursor before referencing it in other statements. You give the cursor a name and associate it with a specific query. You can optionally specify parameters that you use in the WHERE clause instead of referring to local variables.
These parameters can have default values. Example shows how you can declare cursors. Cursors and variables follow the same scoping rules. Naming cursors after database tables is possible but not recommended. A cursor can take parameters, which can appear in the associated query wherever constants can appear. The formal parameters of a cursor must be IN parameters; they supply values in the query, but do not return any values from the query.
As the following example shows, you can initialize cursor parameters to default values. You can pass different numbers of actual parameters to a cursor, accepting or overriding the default values as you please. Also, you can add new formal parameters without having to change existing references to the cursor. Cursor parameters can be referenced only within the query specified in the cursor declaration. The parameter values are used by the associated query when the cursor is opened.
Opening the cursor executes the query and identifies the result set, which consists of all rows that meet the query search criteria. An example of the OPEN statement follows:. Each fetch retrieves the current row and advances the cursor to the next row in the result set.
For each column value returned by the query associated with the cursor, there must be a corresponding, type-compatible variable in the INTO list. Note the use of built-in regular expression functions in the queries. Any variables in the query are evaluated only when the cursor is opened. In Example , each retrieved salary is multiplied by 2 , even though factor is incremented after every fetch.
To change the result set or the values of variables in the query, you must close and reopen the cursor with the input variables set to their new values. However, you can use a different INTO list on separate fetches with the same cursor.
Each fetch retrieves another row and assigns values to the target variables, as shown in Example If you fetch past the last row in the result set, the values of the target variables are undefined. When that happens, no exception is raised. For more information, see "Using Cursor Expressions". In Example , you bulk-fetch from a cursor into two collections. Once a cursor is closed, you can reopen it, which runs the query again with the latest values of any cursor parameters and variables referenced in the WHERE clause.
When appended to the cursor or cursor variable name, these attributes return useful information about the execution of a SQL statement. You can use cursor attributes in procedural statements but not in SQL statements. Explicit cursor attributes return information about the execution of a multi-row query. When an explicit cursor or a cursor variable is opened, the rows that satisfy the associated query are identified and form the result set.
Rows are fetched from the result set. To be safe, you might want to use the following EXIT statement instead:. Thereafter, it yields the number of rows fetched so far. The number is incremented if the last fetch returned a row. In traditional database programming, you process query results using an internal data structure called a cursor.
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 ROWNUM 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. When you query only certain columns, you can store all the results for each column in a separate collection variable.
When you query all the columns of a table, you can store the entire result set in a collection of records, which makes it convenient to loop through the results and refer to different columns. This technique can be very fast, but also very memory-intensive. If you use it often, you might be able to improve your code by doing more of the work in SQL:. If you only need to loop once through the result set, use a FOR loop as described in the following sections. This technique avoids the memory overhead of storing a copy of the result set.
If you are looping through the result set to scan for certain values or filter the results into a smaller set, do this scanning or filtering in the original query instead.
If you are looping through the result set and running another query or a DML statement for each result row, you can probably find a more efficient technique.
Perhaps the most common case of a query is one where you issue the SELECT statement, then immediately loop once through the rows of the result set. The iterator variable for the FOR loop does not need to be declared in advance. When you use expressions rather than explicit column names, use column aliases so that you can refer to the corresponding values inside the loop. You might want to specify a query in one place but retrieve the rows somewhere else, even in another subprogram.
Or you might want to process some rows differently than others, and so need more than a simple loop. Because explicit cursors are so flexible, you can choose from different notations depending on your needs. The following sections describe all the query-processing features that explicit cursors provide. You refer to the fields of this record variable inside the loop.
You can perform tests and calculations, display output, or store the results somewhere else. It does a query to get the name and job Id of employees with manager Ids greater than
Oracle PL/SQL Cursor: Implicit, Explicit, Cursor FOR Loop [Example]
This does not apply to a BULK or multirow operation. Oracle is transaction oriented; that is, Oracle uses transactions to ensure data integrity. A transaction is a series of SQL data manipulation statements that does a logical unit of work. It is important not to allow one operation to succeed while the other fails. At the end of a transaction that makes database changes, Oracle makes all the changes permanent or undoes them all.
Join Stack Overflow to learn, share knowledge, and build your career. Connect and share knowledge within a single location that is structured and easy to search. I have an Oracle stored procedure that has been running for 7 or so years both locally on development instances and on multiple client test and production instances running Oracle 8, then 9, then 10, and recently It has worked consistently until the upgrade to Oracle 11g. Basically, the procedure opens a reference cursor, updates a table then completes. In 10g the cursor will contain the expected results but in 11g the cursor will be empty. This behavior is consistent on every 10g or 11g instance I've tried
New Features in PL/SQL for Oracle Database 10g Release 2 () . .. xxv Differences between the CHAR and VARCHAR2 Datatypes. Declaring REF CURSOR Types and Cursor Variables. Reducing Loop Overhead for DML Statements and Queries with Bulk SQL.
I believe that many DBAs who do development or maintenance have encountered similar problems when looking for a job: simply describe the type of cursor, the difference between a normal cursor and a REF cursor, and when to apply it correctly. This topic, I really puzzled a lot of people, in fact, they are in the specific development of the time, it is still more able to grasp the correct use of the cursor, but that is not to say, of course, this and everyone's own channel flow traffic capacity is related. Some people are not good at speaking, but they are doing well. Pull the pull away, finally nagging: do technology this road, can not say, or will do not packaging, road is not "far". One, explicit type cursor Explicit is relative to the implicit cursor, there is a clear statement of the cursor.
A Cursor is a pointer to this context area. Oracle creates context area for processing an SQL statement which contains all information about the statement. A cursor holds the rows returned by the SQL statement.
By following the steps in this chapter, you can generate the report output shown in Figure For example, if you already have numerous queries built and you want to reuse those queries in your reports, you can simply use a REF CURSOR in your report data model to access those queries.
The difference between cursor and refcursor and sys_refcursor
Knowledge is of two kinds. We know a subject ourselves, or we know where we can find information upon it. Oracle is transaction oriented; that is, Oracle uses transactions to ensure data integrity. A transaction is a series of SQL data manipulation statements that does a logical unit of work. It is important not to allow one operation to succeed while the other fails. At the end of a transaction that makes database changes, Oracle makes all the changes permanent or undoes them all.
It allows declaration of constants and variables , procedures and functions, types and variables of those types, and triggers. It can handle exceptions run-time errors. Implementations from version 8 of Oracle Database onwards have included features associated with object-orientation. These keywords divide the block into a declarative part, an executable part, and an exception-handling part. The declaration section is optional and may be used to define and initialize constants and variables. If a variable is not initialized then it defaults to NULL value. The optional exception-handling part is used to handle run time errors.
Oracle is a registered trademark, and Oracle Store, Oracle9i, PL/SQL, Pro*C, and SQL*Plus are Separating Cursor Specs and Bodies with Packages. For basic Oracle concepts, see Oracle9i Database Concepts. In North TO MONTH represent differences between two date and time values, simplifying.
Oracle Database Data Cartridge Developer's Guide for information about creating aggregate functions for complex data types such as multimedia data stored using object types, opaque types, and LOBs. A block has an optional declarative part, a required executable part, and an optional exception-handling part. A block can be either anonymous or named. If the subprogram has parameters, then their values can differ for each invocation. A subprogram is either a procedure or a function. Typically, you use a procedure to perform an action and a function to compute and return a value.
Stored procedures are stored inside the database. They define a programming interface for the database rather than allowing the client application to interact with database objects directly. Stored procedures are typically used for data validation or to encapsulate large, complex processing instructions that combine several SQL queries. Stored functions have a single return value parameter. Unlike functions, procedures may or may not return values. A package is composed of two distinct pieces:. The specification defines all public items.
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