Добавил:
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз: Предмет: Файл:
Скачиваний:
37
Добавлен:
16.04.2013
Размер:
5.97 Mб
Скачать

SAVEPOINT Statement

SAVEPOINT Statement

The SAVEPOINT statement names and marks the current point in the processing of a transaction. With the ROLLBACK TO statement, savepoints undo parts of a transaction instead of the whole transaction. For more information, see "Overview of Transaction Processing in PL/SQL" on page 6-29.

Syntax

savepoint_statement

SAVEPOINT savepoint_name ;

Keyword and Parameter Description

savepoint_name

An undeclared identifier, which marks the current point in the processing of a transaction.

Usage Notes

A simple rollback or commit erases all savepoints. When you roll back to a savepoint, any savepoints marked after that savepoint are erased. The savepoint to which you roll back remains.

You can reuse savepoint names within a transaction. The savepoint moves from its old position to the current point in the transaction.

If you mark a savepoint within a recursive subprogram, new instances of the SAVEPOINT statement are executed at each level in the recursive descent. You can only roll back to the most recently marked savepoint.

An implicit savepoint is marked before executing an INSERT, UPDATE, or DELETE statement. If the statement fails, a rollback to the implicit savepoint is done. Normally, just the failed SQL statement is rolled back, not the whole transaction; if the statement raises an unhandled exception, the host environment (such as SQL*Plus) determines what is rolled back.

Related Topics

COMMIT Statement, ROLLBACK Statement

PL/SQL Language Elements 13-121

SCN_TO_TIMESTAMP Function

SCN_TO_TIMESTAMP Function

Syntax

return_value := SCN_TO_TIMESTAMP(number);

Purpose

SCN_TO_TIMESTAMP takes an argument that represents a system change number (SCN) and returns the timestamp associated with that SCN. The returned value has the datatype TIMESTAMP.

Usage Notes

This function is part of the flashback query feature. System change numbers provide a precise way to specify the database state at a moment in time, so that you can see the data as it was at that moment.

Call this function to find out the date and time associated with an SCN that you have stored to use with flashback query.

Examples

DECLARE

right_now TIMESTAMP; yesterday TIMESTAMP; sometime TIMESTAMP; scn1 INTEGER; scn2 INTEGER; scn3 INTEGER;

BEGIN

--Get the current SCN. right_now := SYSTIMESTAMP;

scn1 := TIMESTAMP_TO_SCN(right_now); dbms_output.put_line('Current SCN is ' || scn1);

--Get the SCN from exactly 1 day ago. yesterday := right_now - 1;

scn2 := TIMESTAMP_TO_SCN(yesterday); dbms_output.put_line('SCN from yesterday is ' || scn2);

--Find an arbitrary SCN somewhere between yesterday and today.

--(In a real program we would have stored the SCN at some significant moment.) scn3 := (scn1 + scn2) / 2;

--Find out what time that SCN was in effect.

sometime := SCN_TO_TIMESTAMP(scn3);

dbms_output.put_line('SCN ' || scn3 || ' was in effect at ' || TO_CHAR(sometime));

END;

/

Related Topics

TIMESTAMP_TO_SCN Function

13-122 PL/SQL User's Guide and Reference

SELECT INTO Statement

SELECT INTO Statement

The SELECT INTO statement retrieves data from one or more database tables, and assigns the selected values to variables or collections. For a full description of the

SELECT statement, see Oracle Database SQL Reference.

In its default usage (SELECT ... INTO), this statement retrieves one or more columns from a single row. In its bulk usage (SELECT ... BULK COLLECT INTO), this statement retrieves an entire result set at once.

Syntax

select_into_statement

 

 

DISTINCT

 

 

 

 

 

 

UNIQUE

 

 

 

 

 

 

ALL

 

 

 

*

 

 

 

 

 

 

 

 

SELECT

 

 

 

 

 

,

 

 

 

,

 

 

 

select_item

 

 

 

 

 

 

 

 

 

 

variable_name

 

 

 

 

INTO

 

 

 

 

 

 

 

 

record_name

 

 

 

 

 

 

 

 

 

 

 

,

 

 

 

 

 

collection_name

 

BULK COLLECT INTO

 

 

 

 

 

 

 

 

 

:

host_array_name

 

 

 

 

 

 

,

 

 

 

table_reference

 

 

alias

 

 

 

 

 

 

 

 

FROM

(

subquery

 

)

rest_of_statement

;

 

TABLE

(

subquery2

)

 

PL/SQL Language Elements 13-123

SELECT INTO Statement

select_item

 

,

 

 

 

(

parameter_name

)

 

function_name

 

 

 

 

NULL

 

 

 

 

numeric_literal

 

 

 

 

schema_name

.

table_name

 

AS

 

 

.

*

 

 

view_name

 

alias

schema_name

.

table_name

 

 

 

 

 

.

 

 

 

view_name

 

 

 

 

 

 

column_name

CURRVAL sequence_name .

NEXTVAL

' text '

Keyword and Parameter Description

alias

Another (usually short) name for the referenced column, table, or view.

BULK COLLECT

Stores result values in one or more collections, for faster queries than loops with FETCH statements. For more information, see "Reducing Loop Overhead for DML Statements and Queries (FORALL, BULK COLLECT)" on page 11-7.

collection_name

A declared collection into which select_item values are fetched. For each select_item, there must be a corresponding, type-compatible collection in the list.

function_name

A user-defined function.

host_array_name

An array (declared in a PL/SQL host environment and passed to PL/SQL as a bind variable) into which select_item values are fetched. For each select_item, there must be a corresponding, type-compatible array in the list. Host arrays must be prefixed with a colon.

numeric_literal

A literal that represents a number or a value implicitly convertible to a number.

parameter_name

A formal parameter of a user-defined function.

13-124 PL/SQL User's Guide and Reference

SELECT INTO Statement

record_name

A user-defined or %ROWTYPE record into which rows of values are fetched. For each select_item value returned by the query, there must be a corresponding, type-compatible field in the record.

rest_of_statement

Anything that can follow the FROM clause in a SQL SELECT statement (except the SAMPLE clause).

schema_name

The schema containing the table or view. If you omit schema_name, Oracle assumes the table or view is in your schema.

subquery

A SELECT statement that provides a set of rows for processing. Its syntax is like that of select_into_statement without the INTO clause. See "SELECT INTO Statement" on page 13-123.

table_reference

A table or view that must be accessible when you execute the SELECT statement, and for which you must have SELECT privileges. For the syntax of table_reference, see "DELETE Statement" on page 13-41.

TABLE (subquery2)

The operand of TABLE is a SELECT statement that returns a single column value, which must be a nested table or a varray. Operator TABLE informs Oracle that the value is a collection, not a scalar value.

variable_name

A previously declared variable into which a select_item value is fetched. For each select_item value returned by the query, there must be a corresponding, type-compatible variable in the list.

Usage Notes

By default, a SELECT INTO statement must return only one row. Otherwise, PL/SQL raises the predefined exception TOO_MANY_ROWS and the values of the variables in the INTO clause are undefined. Make sure your WHERE clause is specific enough to only match one row

If no rows are returned, PL/SQL raises NO_DATA_FOUND. You can guard against this exception by selecting the result of an aggregate function, such as COUNT(*) or AVG(), where practical. These functions are guaranteed to return a single value, even if no rows match the condition.

A SELECT ... BULK COLLECT INTO statement can return multiple rows. You must set up collection variables to hold the results. You can declare associative arrays or nested tables that grow as needed to hold the entire result set.

The implicit cursor SQL and its attributes %NOTFOUND, %FOUND, %ROWCOUNT, and %ISOPEN provide information about the execution of a SELECT INTO statement.

PL/SQL Language Elements 13-125

SELECT INTO Statement

Examples

The following example demonstrates using the SELECT INTO statement to query a single value into a PL/SQL variable, entire columns into PL/SQL collections, or entire rows into a PL/SQL collection of records:

DECLARE

howmany NUMBER;

some_first employees.first_name%TYPE; some_last employees.last_name%TYPE; some_employee employees%ROWTYPE;

TYPE first_typ IS TABLE OF employees.first_name%TYPE INDEX BY PLS_INTEGER; TYPE last_typ IS TABLE OF employees.first_name%TYPE INDEX BY PLS_INTEGER; first_names first_typ;

last_names last_typ;

CURSOR c1 IS SELECT first_name, last_name FROM employees; TYPE name_typ IS TABLE OF c1%ROWTYPE INDEX BY PLS_INTEGER; all_names name_typ;

TYPE emp_typ IS TABLE OF employees%ROWTYPE INDEX BY PLS_INTEGER; all_employees emp_typ;

BEGIN

--Query a single value and store it in a variable. SELECT COUNT(*) INTO howmany FROM user_tables;

dbms_output.put_line('This schema owns ' || howmany || ' tables.');

--Query multiple columns from one row, and store them in variables. SELECT first_name, last_name INTO some_first, some_last

FROM employees WHERE ROWNUM < 2; dbms_output.put_line('Random employee: ' || some_first ||

'' || some_last);

--Query a single row and store it in a record.

SELECT * INTO some_employee FROM employees WHERE ROWNUM < 2;

--Query multiple columns from multiple rows, and store them in a collection

--of records.

SELECT first_name, last_name BULK COLLECT INTO all_names FROM EMPLOYEES;

--Query multiple columns from multiple rows, and store them in separate

--collections. (Generally less useful than a single collection of records.) SELECT first_name, last_name

BULK COLLECT INTO first_names, last_names FROM EMPLOYEES;

--Query an entire (small!) table and store the rows

--in a collection of records. Now you can manipulate the data

--in-memory without any more I/O.

SELECT * BULK COLLECT INTO all_employees FROM employees; END;

/

Related Topics

Assignment Statement, FETCH Statement, %ROWTYPE Attribute

13-126 PL/SQL User's Guide and Reference

Соседние файлы в папке Oracle 10g