Manage standard views

This topic describes how to create, modify, and drop views.

A view displays the result of a query. You can use views in most cases where you can use tables. If the data you frequently access is distributed across multiple tables, a view is the best choice.

Create a standard view

You can execute the CREATE VIEW statement to create a standard view. After a view is created, you can execute DML statements on it.

The SQL syntax for creating a view in Oracle mode is as follows:

create_view_stmt:
  CREATE [OR REPLACE] [[NO] FORCE] VIEW view_name [(column_name_list)] AS select_stmt;

column_name_list:
    column_name [, column_name ...]

The parameters are described as follows:

• OR REPLACE: specifies to re-create a view that already exists by using a new definition.

• select_stmt: defines the SELECT statement of the view. You can obtain the information to be used in this statement from a base table or other views.

  Note

  • When you create a view in Oracle mode of OceanBase Database, you can use the --string option to add a comment to the view. The comment is stored in the view definition.
    • You can add --string to any position in select_stmt.

  • [NO] FORCE: If you are not sure whether the view to be created involves base tables or referenced object types, or whether the owner of the schema of the view has required privileges, you must specify FORCE.

    If base tables are involved, and the owner of the schema of the view has required privileges, you can specify NO FORCE. The default value is NO FORCE.

  • column_name_list: the unique column names used in the view. Each base table must also have unique column names. By default, the column names retrieved by the SELECT statement are used as the column names in the view.

    You can also use the optional column_name_list clause to define column names for a view. Separate multiple column names with commas (,). The number of column names in column_name_list must be equal to the number of columns retrieved by the SELECT statement.

    The SELECT statement can directly reference the columns of a table. You can also use functions, constants, and operators in the statement to retrieve columns.

  Here are some examples:

  • Retrieve the col1 and col2 columns of the tbl1 table to create a view named view1.

    obclient> CREATE OR REPLACE FORCE VIEW view1(vcol1, vcol2) AS SELECT col1, col2 FROM tbl1;
    

  • Create a view named view3 based on the col1 and col2 columns of the tbl2 table, and add comments to view3.

    1. Create a table named tbl2.

       obclient [SYS]> CREATE TABLE tbl2 (col1 INT, col2 INT);
       

    2. Create a view named view4.

       obclient [SYS]> CREATE VIEW view4
         AS SELECT col1, --col1 comment1
           col2 --col1 comment2
           FROM tbl2;
       

  Modify a standard view

  You can execute the CREATE OR REPLACE VIEW statement to modify a standard view.

  Example: Modify the stock_item view.

  obclient> CREATE OR REPLACE VIEW stock_item
       AS
       SELECT /*+ leading(s) use_merge(i) */
       i_price, i_name, i_data, s_i_id, s_w_id, s_order_cnt, s_ytd, s_remote_cnt, s_quantity, s_data, s_dist_01, s_dist_02, s_dist_03, s_dist_04, s_dist_05, s_dist_06, s_dist_07, s_dist_08, s_dist_09, s_dist_10
       FROM stok s, item i
       WHERE s.s_i_id = i.i_id;
  Query OK, 0 rows affected (0.02 sec)
  

  Drop a view

  You can execute the DROP VIEW statement to drop one or more views at a time. When a view is dropped, tables referenced by the view are not dropped.

  If you drop a view that is referenced by another view, queries on the view that references the dropped view fail.

  Before you drop a view, make sure that you have the DROP privilege on the view.

  The SQL syntax for dropping a view in Oracle mode is as follows:

  obclient>DROP VIEW view_name;
  

  Example: Drop the v1 view.

  obclient> DROP VIEW v1;
  

  References

  • CREATE VIEW

  • DROP VIEW