ITPub博客

首页 > Linux操作系统 > Linux操作系统 > MERGE INTO 官方文档

MERGE INTO 官方文档

原创 Linux操作系统 作者:perfychi 时间:2013-08-12 13:49:28 0 删除 编辑
Purpose

Use the MERGE statement to select rows from one or more sources for update or insertion into a table or view. You can specify conditions to determine whether to update or insert into the target table or view.

This statement is a convenient way to combine multiple operations. It lets you avoid multiple INSERT, UPDATE, and DELETE DML statements.

MERGE is a deterministic statement. That is, you cannot update the same row of the target table multiple times in the same MERGE statement.

Note:

Oracle Database does not implement fine-grained access control during MERGE statements. If you are using the fine-grained access control feature on the target table or tables, use equivalent INSERT and UPDATE statements instead of MERGE to avoid error messages and to ensure correct access control.

Prerequisites

You must have the INSERT and UPDATE object privileges on the target table and the SELECT object privilege on the source table. To specify the DELETE clause of the merge_update_clause, you must also have the DELETE object privilege on the target table.

Syntax

merge::=

De.ion of merge.gif follows
Description of the illustration merge.gif

(merge_update_clause ::=, merge_insert_clause ::=, error_logging_clause ::=

merge_update_clause ::=

De.ion of merge_update_clause.gif follows
Description of the illustration merge_update_clause.gif

merge_insert_clause ::=

De.ion of merge_insert_clause.gif follows
Description of the illustration merge_insert_clause.gif

where_clause::=

De.ion of where_clause.gif follows
Description of the illustration where_clause.gif

error_logging_clause ::=

De.ion of error_logging_clause.gif follows
Description of the illustration error_logging_clause.gif

Semantics

INTO Clause

Use the INTO clause to specify the target table or view you are updating or inserting into. In order to merge data into a view, the view must be updatable. Please refer to "Notes on Updatable Views" for more information.

USING Clause

Use the USING clause to specify the source of the data to be updated or inserted. The source can be a table, view, or the result of a subquery.

ON Clause

Use the ON clause to specify the condition upon which the MERGE operation either updates or inserts. For each row in the target table for which the search condition is true, Oracle Database updates the row with corresponding data from the source table. If the condition is not true for any rows, then the database inserts into the target table based on the corresponding source table row.

merge_update_clause

The merge_update_clause specifies the new column values of the target table. Oracle performs this update if the condition of the ON clause is true. If the update clause is executed, then all update triggers defined on the target table are activated.

Specify the where_clause if you want the database to execute the update operation only if the specified condition is true. The condition can refer to either the data source or the target table. If the condition is not true, then the database skips the update operation when merging the row into the table.

Specify the DELETE where_clause to clean up data in a table while populating or updating it. The only rows affected by this clause are those rows in the destination table that are updated by the merge operation. That is, the DELETE WHERE condition evaluates the updated value, not the original value that was evaluated by the UPDATE SET ... WHERE condition. If a row of the destination table meets the DELETE condition but is not included in the join defined by the ON clause, then it is not deleted. Any delete triggers defined on the target table will be activated for each row deletion.

You can specify this clause by itself or with the merge_insert_clause. If you specify both, then they can be in either order.

Restrictions on the merge_update_clause This clause is subject to the following restrictions:

  • You cannot update a column that is referenced in the ON condition clause.

  • You cannot specify DEFAULT when updating a view.

merge_insert_clause

The merge_insert_clause specifies values to insert into the column of the target table if the condition of the ON clause is false. If the insert clause is executed, then all insert triggers defined on the target table are activated. If you omit the column list after the INSERT keyword, then the number of columns in the target table must match the number of values in the VALUES clause.

To insert all of the source rows into the table, you can use a constant filter predicate in the ON clause condition. An example of a constant filter predicate is ON (0=1). Oracle Database recognizes such a predicate and makes an unconditional insert of all source rows into the table. This approach is different from omitting the merge_update_clause. In that case, the database still must perform. a join. With constant filter predicate, no join is performed.

Specify the where_clause if you want Oracle Database to execute the insert operation only if the specified condition is true. The condition can refer only to the data source table. Oracle Database skips the insert operation for all rows for which the condition is not true.

You can specify this clause by itself or with the merge_update_clause. If you specify both, then they can be in either order.

Restriction on Merging into a View You cannot specify DEFAULT when updating a view.

error_logging_clause

The error_logging_clause has the same behavior. in a MERGE statement as in an INSERT statement. Please refer to the INSERT statement error_logging_clause for more information.

Examples

Merging into a Table: Example The following example uses the bonuses table in the sample schema oe with a default bonus of 100. It then inserts into the bonuses table all employees who made sales, based on the sales_rep_id column of the oe.orders table. Finally, the human resources manager decides that employees with a salary of $8000 or less should receive a bonus. Those who have not made sales get a bonus of 1% of their salary. Those who already made sales get an increase in their bonus equal to 1% of their salary. The MERGE statement implements these changes in one step:

CREATE TABLE bonuses (employee_id NUMBER, bonus NUMBER DEFAULT 100);

INSERT INTO bonuses(employee_id)
   (SELECT e.employee_id FROM employees e, orders o
   WHERE e.employee_id = o.sales_rep_id
   GROUP BY e.employee_id); 

SELECT * FROM bonuses;

EMPLOYEE_ID      BONUS
----------- ----------
        153        100
        154        100
        155        100
        156        100
        158        100
        159        100
        160        100
        161        100
        163        100

MERGE INTO bonuses D
   USING (SELECT employee_id, salary, department_id FROM employees
   WHERE department_id = 80) S
   ON (D.employee_id = S.employee_id)
   
WHEN MATCHED THEN
UPDATE SET D.bonus = D.bonus + S.salary*.01
DELETE WHERE (S.salary > 8000)

WHEN NOT MATCHED THEN
INSERT (D.employee_id, D.bonus) VALUES (S.employee_id, S.salary*0.1) WHERE (S.salary <= 8000); EMPLOYEE_ID BONUS ----------- ---------- 153 180 154 175 155 170 159 180 160 175 161 170 179 620 173 610 165 680 166 640 164 720 172 730 167 620 171 740

来自 “ ITPUB博客 ” ,链接:http://blog.itpub.net/27042095/viewspace-768288/,如需转载,请注明出处,否则将追究法律责任。

请登录后发表评论 登录
全部评论

注册时间:2012-06-06

  • 博文量
    486
  • 访问量
    2682916