Create a materialized view

This topic describes how to create a materialized view by using SQL statements.

Privilege requirements

To create a materialized view, you must have the CREATE TABLE privilege. For more information about the privileges of OceanBase Database, see Privilege types in Oracle mode.

Syntax

The syntax for creating a materialized view is as follows:

CREATE MATERIALIZED VIEW view_name [([column_list] [PRIMARY KEY(column_list)])]
    [table_option_list]
    [partition_option]
    [mv_column_group_option]
    [refresh_clause [query_rewrite_clause] [on_query_computation_clause]]
    AS view_select_stmt;

Parameters:

• view_name: specifies the name of the materialized view to be created.

• column_list: an optional parameter that specifies the list of columns in the materialized view. If you want to specify explicit names for the view columns, you can use the column_list clause and separate the column names with commas.

• PRIMARY KEY(column_list): an optional parameter that specifies the primary key of the materialized view.

• table_option_list: an optional parameter that specifies the table options for the materialized view.

• partition_option: an optional parameter that specifies the partitioning options for the materialized view.

• mv_column_group_option: an optional parameter that specifies the storage format of the materialized view. If not specified, the default is to create a row-based materialized view.

• refresh_clause [query_rewrite_clause] [on_query_computation_clause]: an optional parameter that specifies the following options:

  • refresh_clause: specifies the refresh method for the materialized view.
  • query_rewrite_clause: an optional parameter that specifies whether to enable automatic query rewriting for the materialized view.
  • on_query_computation_clause: an optional parameter that specifies whether the materialized view is a regular materialized view or a real-time materialized view.

• AS view_select_stmt: specifies the query (SELECT) statement used to define the data of the materialized view. This statement retrieves data from the base table and stores the results in the materialized view.

  Note

  For OceanBase Database V4.3.5:

  • Starting from V4.3.5 BP2, you can create a full-refresh materialized view with a standard view or an external table as the base table.
  • Starting from V4.3.5 BP4, you can add the AS OF PROCTIME() clause to the base table when creating a materialized view. If you use AS OF PROCTIME() outside the base table of the materialized view, an error will be returned. AS OF PROCTIME() is used to specify that the incremental refresh should skip this table, and a table with AS OF PROCTIME() does not need to create an mlog.
  • Starting from V4.3.5 BP5, when a standard view is declared as a dimension table (AS OF PROCTIME()), it can serve as the base table for an incremental-refresh materialized view.

For more information about the syntax for creating a materialized view, see CREATE MATERIALIZED VIEW.

Create a materialized view

Create a regular materialized view

To create a regular materialized view, omit or specify the DISABLE ON QUERY COMPUTATION clause.

Here is an example:

1. Create a table named tbl1 as the base table for the materialized view. The following example creates the tbl1 table:

   CREATE TABLE tbl1 (col1 NUMBER PRIMARY KEY, col2 VARCHAR2(20), col3 NUMBER);
   

2. Create a materialized view named mv_tbl1 based on the tbl1 table. The following example creates the mv_tbl1 materialized view:

   CREATE MATERIALIZED VIEW mv_tbl1
       AS SELECT col1, col2
         FROM tbl1
         WHERE col3 >= 20;
   

   or

   CREATE MATERIALIZED VIEW mv_tbl1
       REFRESH FORCE
       DISABLE ON QUERY COMPUTATION
       AS SELECT col1, col2
         FROM tbl1
         WHERE col3 >= 20;
   

Create a nested materialized view

A nested materialized view is a materialized view that is built on an existing materialized view. For example, in the following figure, the mv1 materialized view is built based on the tbl1 and tbl2 tables, which is a typical materialized view. The mv2 materialized view is built based on the mv1 materialized view and the tbl3 table, which is a nested materialized view. Similarly, the mv3 materialized view is built based on the mv1 and mv2 materialized views, which is also a nested materialized view. The following figure shows this.

In OceanBase Database V4.3.5, starting from V4.3.5 BP3, you can specify the refresh strategy for a nested materialized view. Valid values are as follows:

• INDIVIDUAL: the default value, indicating independent refresh.
• INCONSISTENT: indicating cascading inconsistent refresh.
• CONSISTENT: indicating cascading consistent refresh.

Limitations on nested materialized views

• To support incremental refresh for nested materialized views, you must create mlogs on the materialized view (base table).
• If a materialized view is fully refreshed, the dependent materialized view (nested materialized view) must be fully refreshed before incremental refresh is performed. Otherwise, an error is returned.
• If a materialized view (nested materialized view) is a real-time materialized view, you must perform incremental refresh on the underlying materialized view to update the mlog. The query results of a real-time materialized view are obtained by simulating the mlog to merge the results of the underlying materialized view and itself. Therefore, you must perform incremental refresh on the underlying materialized view to update the mlog to ensure that the data of the real-time materialized view is up-to-date.

Here is an example:

1. Create a table named tbl3 as the base table for the materialized view. The following example creates the tbl3 table:

   CREATE TABLE tbl3(id INT, name VARCHAR2(30), PRIMARY KEY(id));
   

2. Create a table named tbl4 as the base table for the materialized view. The following example creates the tbl4 table:

   CREATE TABLE tbl4(id INT, age INT, PRIMARY KEY(id));
   

3. Create a materialized view named mv1_tbl3_tbl4 based on the tbl3 and tbl4 tables. The following example creates the mv1_tbl3_tbl4 materialized view:

   CREATE MATERIALIZED VIEW mv1_tbl3_tbl4 (PRIMARY KEY (id1, id2))
       REFRESH COMPLETE
       AS SELECT tbl3.id id1, tbl4.id id2, tbl3.name, tbl4.age
           FROM tbl3, tbl4
           WHERE tbl3.id = tbl4.id;
   

4. Create a materialized view named mv_mv1_tbl3_tbl4 based on the mv1_tbl3_tbl4 materialized view. The following example creates the mv_mv1_tbl3_tbl4 materialized view:

   CREATE MATERIALIZED VIEW mv_mv1_tbl3_tbl4
       REFRESH COMPLETE
       AS SELECT SUM(AGE) age_sum
           FROM mv1_tbl3_tbl4;
   

5. Create a materialized view named mv1_mv1_tbl3_tbl4 based on the mv1_tbl3_tbl4 materialized view. The refresh strategy is set to INCONSISTENT. The following example creates the mv1_mv1_tbl3_tbl4 materialized view:

   CREATE MATERIALIZED VIEW mv1_mv1_tbl3_tbl4
       REFRESH COMPLETE INCONSISTENT
       AS SELECT SUM(AGE) age_sum
           FROM mv1_tbl3_tbl4;
   

Create a real-time materialized view

To create a real-time materialized view, specify the ENABLE ON QUERY COMPUTATION clause.

Considerations

• Before you create a real-time materialized view, you must create a materialized view log for each base table that is referenced by the materialized view.

  Note

  For OceanBase Database V4.3.5, the automatic management of materialized view logs is supported starting from V4.3.5 BP4. If you enable automatic management of materialized view logs, you do not need to create materialized view logs for base tables before you create a real-time materialized view. OceanBase Database automatically creates materialized view logs or updates the definitions of existing materialized view logs to include the columns required by the new real-time materialized view. For more information, see Automatic management of materialized view logs.

• Only specific types of materialized views can be specified as real-time materialized views. If you specify a materialized view that does not meet the requirements as a real-time materialized view, an error is returned. The requirements for a real-time materialized view are the same as those for an incrementally refreshed materialized view. For more information, see the Basic requirements for incremental refresh section in Refresh a materialized view.

• If a materialized view (nested materialized view) is a real-time materialized view, you must incrementally refresh the lower-level materialized view to update the materialized view log (mlog). The query results of a real-time materialized view are obtained by simulating the mlog and merging the query results of the lower-level materialized view and itself. Therefore, you must incrementally refresh the lower-level materialized view to update the mlog, so that the data of the real-time materialized view is the latest.

Here is an example:

1. Create a table named tbl2 as the base table of the materialized view.

   CREATE TABLE tbl2(col1 INT, col2 INT, col3 INT);
   

2. Create a materialized view log on the tbl2 table.

   CREATE MATERIALIZED VIEW LOG ON tbl2
       WITH PRIMARY KEY, ROWID, SEQUENCE (col1, col2, col3) INCLUDING NEW VALUES;
   

3. Create a real-time materialized view named mv_tbl2 based on the tbl2 table.

   CREATE MATERIALIZED VIEW mv_tbl2
       REFRESH COMPLETE ON DEMAND
       ENABLE ON QUERY COMPUTATION
       AS SELECT col1, count(*) AS cnt
          FROM tbl2
          GROUP BY col1;
   

4. After you create the real-time materialized view, you can view the materialized view in the DBA_MVIEWS view to check whether it is a real-time materialized view.

   SELECT MVIEW_NAME, ON_QUERY_COMPUTATION
   FROM sys.DBA_MVIEWS
   WHERE MVIEW_NAME = 'MV_TBL2';
   

   Notice

   In Oracle mode, when the value of the MVIEW_NAME field in the sys.DBA_MVIEWS view matches the name of a table, the table name must be in uppercase.

   The returned result is as follows:

   +------------+----------------------+
   | MVIEW_NAME | ON_QUERY_COMPUTATION |
   +------------+----------------------+
   | MV_TBL2    | Y                    |
   +------------+----------------------+
   1 row in set
   

5. View the execution plan of the real-time materialized view.

   EXPLAIN BASIC SELECT * FROM mv_tbl2;
   

   From the following execution plan, you can see that data is read from the materialized view and the mlog of the base table referenced by the view during execution. The two parts of data are calculated and integrated to obtain the real-time data of the materialized view.

   The returned result is as follows:

   +----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | Query Plan                                                                                                                                                                       |
   +----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | ==============================================                                                                                                                                   |
   | |ID|OPERATOR                   |NAME         |                                                                                                                                   |
   | ----------------------------------------------                                                                                                                                   |
   | |0 |HASH GROUP BY              |             |                                                                                                                                   |
   | |1 |└─SUBPLAN SCAN             |INNER_RT_MV$$|                                                                                                                                   |
   | |2 |  └─UNION ALL              |             |                                                                                                                                   |
   | |3 |    ├─TABLE FULL SCAN      |MV_TBL2      |                                                                                                                                   |
   | |4 |    └─HASH GROUP BY        |             |                                                                                                                                   |
   | |5 |      └─SUBPLAN SCAN       |DLT_T$$      |                                                                                                                                   |
   | |6 |        └─WINDOW FUNCTION  |             |                                                                                                                                   |
   | |7 |          └─TABLE FULL SCAN|MLOG$_TBL2   |                                                                                                                                   |
   | ==============================================                                                                                                                                   |
   | Outputs & filters:                                                                                                                                                               |
   | -------------------------------------                                                                                                                                            |
   |   0 - output([INNER_RT_MV$$.COL1], [cast(T_FUN_SUM(INNER_RT_MV$$.CNT), NUMBER(38, 0))]), filter([T_FUN_SUM(INNER_RT_MV$$.CNT) > cast(0, NUMBER(-1, -85))]), rowset=16            |
   |       group([INNER_RT_MV$$.COL1]), agg_func([T_FUN_SUM(INNER_RT_MV$$.CNT)])                                                                                                      |
   |   1 - output([INNER_RT_MV$$.COL1], [INNER_RT_MV$$.CNT]), filter(nil), rowset=16                                                                                                  |
   |       access([INNER_RT_MV$$.COL1], [INNER_RT_MV$$.CNT])                                                                                                                          |
   |   2 - output([UNION([1])], [UNION([2])]), filter(nil), rowset=16                                                                                                                 |
   |   3 - output([MV_TBL2.COL1], [MV_TBL2.CNT]), filter(nil), rowset=16                                                                                                              |
   |       access([MV_TBL2.COL1], [MV_TBL2.CNT]), partitions(p0)                                                                                                                      |
   |       is_index_back=false, is_global_index=false,                                                                                                                                |
   |       range_key([MV_TBL2.__pk_increment]), range(MIN ; MAX)always true                                                                                                           |
   |   4 - output([DLT_T$$.COL1], [T_FUN_SUM(CASE WHEN DLT_T$$.OLD_NEW$$ = cast('N', VARCHAR2(1048576 )) THEN cast(1, NUMBER(-1, -85)) ELSE (T_OP_NEG, cast(1,                        |
   |        NUMBER(-1, -85))) END)]), filter(nil), rowset=16                                                                                                                          |
   |       group([DLT_T$$.COL1]), agg_func([T_FUN_SUM(CASE WHEN DLT_T$$.OLD_NEW$$ = cast('N', VARCHAR2(1048576 )) THEN cast(1, NUMBER(-1, -85)) ELSE (T_OP_NEG,                       |
   |        cast(1, NUMBER(-1, -85))) END)])                                                                                                                                          |
   |   5 - output([DLT_T$$.OLD_NEW$$], [DLT_T$$.COL1]), filter([DLT_T$$.OLD_NEW$$ = cast('N', VARCHAR2(1048576 )) AND DLT_T$$.SEQUENCE$$ = DLT_T$$.MAXSEQ$$ OR                        |
   |       DLT_T$$.OLD_NEW$$ = cast('O', VARCHAR2(1048576 )) AND DLT_T$$.SEQUENCE$$ = DLT_T$$.MINSEQ$$]), rowset=16                                                                   |
   |       access([DLT_T$$.OLD_NEW$$], [DLT_T$$.SEQUENCE$$], [DLT_T$$.MAXSEQ$$], [DLT_T$$.MINSEQ$$], [DLT_T$$.COL1])                                                                  |
   |   6 - output([MLOG$_TBL2.OLD_NEW$$], [MLOG$_TBL2.SEQUENCE$$], [T_FUN_MAX(MLOG$_TBL2.SEQUENCE$$)], [T_FUN_MIN(MLOG$_TBL2.SEQUENCE$$)], [MLOG$_TBL2.COL1]), filter(nil), rowset=16 |
   |       win_expr(T_FUN_MAX(MLOG$_TBL2.SEQUENCE$$)), partition_by([MLOG$_TBL2.M_ROW$$]), order_by(nil), window_type(RANGE), upper(UNBOUNDED PRECEDING), lower(UNBOUNDED             |
   |       FOLLOWING)                                                                                                                                                                 |
   |       win_expr(T_FUN_MIN(MLOG$_TBL2.SEQUENCE$$)), partition_by([MLOG$_TBL2.M_ROW$$]), order_by(nil), window_type(RANGE), upper(UNBOUNDED PRECEDING), lower(UNBOUNDED             |
   |       FOLLOWING)                                                                                                                                                                 |
   |   7 - output([MLOG$_TBL2.M_ROW$$], [MLOG$_TBL2.SEQUENCE$$], [MLOG$_TBL2.OLD_NEW$$], [MLOG$_TBL2.COL1], [ORA_ROWSCN]), filter([cast(ORA_ROWSCN, NUMBER(-1,                        |
   |        -1)) > last_refresh_scn(500155)]), rowset=16                                                                                                                              |
   |       access([MLOG$_TBL2.M_ROW$$], [MLOG$_TBL2.SEQUENCE$$], [MLOG$_TBL2.OLD_NEW$$], [MLOG$_TBL2.COL1], [ORA_ROWSCN]), partitions(p0)                                             |
   |       is_index_back=false, is_global_index=false, filter_before_indexback[false],                                                                                                |
   |       range_key([MLOG$_TBL2.M_ROW$$], [MLOG$_TBL2.SEQUENCE$$]), range(MIN,MIN ; MAX,MAX)always true                                                                              |
   +----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
   40 rows in set
   

Create a materialized view that enables query rewrite

When you create a materialized view, you can specify the ENABLE QUERY REWRITE clause to enable automatic query rewrite for the materialized view. For more information about query rewrite and rewrite control, see Query rewrite of materialized views.

Here is an example:

1. Create a materialized view named mv_spj_tbl1 based on the tbl1 table and enable automatic query rewrite for the materialized view.

   CREATE MATERIALIZED VIEW mv_spj_tbl1
       NEVER REFRESH
       ENABLE QUERY REWRITE
       AS SELECT *
          FROM tbl1;
   

2. After the materialized view is created, you can query the DBA_MVIEWS view to check whether automatic query rewrite is enabled for the materialized view.

   SELECT MVIEW_NAME, REWRITE_ENABLED
   FROM sys.DBA_MVIEWS
   WHERE MVIEW_NAME = 'MV_SPJ_TBL1';
   

   Notice

   In Oracle mode, when the sys.DBA_MVIEWS view's MVIEW_NAME field matches the table name, the table name must be in uppercase.

   The return result is as follows:

   +-------------+-----------------+
   | MVIEW_NAME  | REWRITE_ENABLED |
   +-------------+-----------------+
   | MV_SPJ_TBL1 | Y               |
   +-------------+-----------------+
   1 row in set
   

Create a columnstore materialized view

OceanBase Database supports materialized views in rowstore, columnstore, and rowstore-columnstore redundant formats. You can specify the mv_column_group_option option to explicitly create a columnstore or rowstore-columnstore redundant materialized view. If a materialized view is a wide table formed by joining multiple tables, creating a columnstore materialized view can improve the performance of some queries. You can specify WITH COLUMN GROUP(each column) to create a columnstore materialized view.

Here is an example:

Create a columnstore materialized view named mv_ec_tbl1 based on the tbl1 table.

CREATE MATERIALIZED VIEW mv_ec_tbl1
    WITH COLUMN GROUP(each column)
    AS SELECT *
       FROM tbl1;

Add a primary key when you create a materialized view

Here is an example:

Create a materialized view named mv_pk_tbl1 based on the tbl1 table and specify a primary key for the view.

CREATE MATERIALIZED VIEW mv_pk_tbl1(v_id, v_name, PRIMARY KEY(v_id))
    AS SELECT col1, col2
       FROM tbl1
       WHERE col3 >= 20;

Add table options and partitioning options when you create a materialized view

When you create a materialized view, you can set table options and design and configure suitable partitioning options based on the data characteristics and access patterns to improve query performance and management efficiency.

For more information about the table options and partitioning options, see CREATE TABLE.

Here is an example:

Create a materialized view named mv_pp_tbl1 based on the tbl1 table. Set the parallelism of the materialized view to 5, and hash partition the materialized view by the col1 column into 8 partitions. Query the records in the tbl1 table that satisfy the condition col3 >= 20 as the base table, and use the query results as the data of the materialized view.

CREATE MATERIALIZED VIEW mv_pp_tbl1
    PARALLEL 5
    PARTITION BY HASH(col1) PARTITIONS 8
    AS SELECT col1, col2
       FROM tbl1
       WHERE col3 >= 20;

Add an index to a materialized view

You cannot directly create an index in the statement for creating a materialized view. You can use the CREATE INDEX statement to create an index for a materialized view.

Here is an example:

Create an index named idx_mv_tbl1 on the col1 column of the materialized view mv_tbl1.

CREATE INDEX idx_mv_tbl1 ON mv_tbl1(col1);

Refresh a materialized view

OceanBase Database supports the following refresh strategies for materialized views: full refresh, incremental refresh, hybrid refresh, and no refresh.

• Full refresh: Recomputes all data in the materialized view to ensure that the data in the view is consistent with the source table.
• Incremental refresh: Refreshes only the data that is affected by changes in the source table, without recomputing the entire view.
• Hybrid refresh: The default option. First, it attempts an incremental refresh. If the incremental refresh fails, it performs a full refresh.
• No refresh: The materialized view is refreshed only when it is created and cannot be refreshed again after creation.

For more information about how to refresh a materialized view, see Refresh a materialized view.

Create a materialized view with a complete refresh strategy

When you create a materialized view, you can use the REFRESH COMPLETE clause to set the refresh strategy to complete refresh.

Here is an example:

Create a materialized view named mv_rc_tbl1 based on table tbl1, set the refresh strategy to complete refresh (REFRESH COMPLETE), and specify col1 and col2 as the data source of the materialized view, which are selected from tbl1 where col3 is greater than or equal to 20.

CREATE MATERIALIZED VIEW mv_rc_tbl1
    REFRESH COMPLETE
    AS SELECT col1, col2
       FROM tbl1
       WHERE col3 >= 20;

Create a materialized view with a complete refresh strategy based on an external table

OceanBase Database V4.3.5 BP2 and later allow you to create a materialized view with a complete refresh strategy based on an external table.

For more information about external tables, see About external tables.

Here is an example:

The following example shows how to create an external table in the local file system and in the Oracle mode of OceanBase Database. The steps are as follows:

1. Prepare an external file.

   Execute the following command to create a file named ext_tbl1.csv in the /home/admin/external_csv directory on the server where the OBServer node is located.

   [admin@xxx /home/admin/external_csv]# vi ext_tbl1.csv
   

   The content of the file is as follows:

   1,'A1'
   2,'A2'
   3,'A3'
   

2. Set the import file path.

   Notice

   Due to security reasons, you can only modify the secure_file_priv system variable by executing an SQL statement through a local Unix socket. For more information, see secure_file_priv.

   1. Execute the following command to log in to the server where the OBServer node is located.

      ssh admin@10.10.10.1
      

   2. Execute the following command to connect to the oracle001 tenant through a local Unix socket.

      obclient -S /home/admin/oceanbase/run/sql.sock -usys@oracle001 -p******
      

   3. Execute the following SQL statement to set the import path to /home/admin/external_csv.

      SET GLOBAL secure_file_priv = "/home/admin/external_csv";
      

3. Reconnect to the oracle001 tenant.

   Here is an example:

   obclient -h10.10.10.1 -P2881 -usys@oracle001 -p****** -A
   

4. Create an external table named ext_tbl1.

   CREATE EXTERNAL TABLE ext_tbl1 ( 
       id INT, 
       name VARCHAR2(50)
       )
       LOCATION = '/home/admin/external_csv'
       FORMAT = (
         TYPE = 'CSV'
         FIELD_DELIMITER = ','
         FIELD_OPTIONALLY_ENCLOSED_BY =''''
         )
       PATTERN = 'ext_tbl1.csv';
   

5. Create a materialized view named mv_ext_tbl1 with a complete refresh strategy based on the external table ext_tbl1.

   CREATE MATERIALIZED VIEW mv_ext_tbl1
       REFRESH COMPLETE
       AS SELECT *
           FROM ext_tbl1;
   

6. Query the data in the materialized view mv_ext_tbl1.

   SELECT * FROM mv_ext_tbl1;
   

   The return result is as follows:

   +------+------+
   | ID   | NAME |
   +------+------+
   |    2 | A2   |
   |    1 | A1   |
   |    3 | A3   |
   +------+------+
   3 rows in set
   

Create a materialized view with incremental refresh

When you create a materialized view, you can use the REFRESH FAST clause to set the refresh strategy to incremental refresh.

Considerations

• At present, incremental refresh is supported for materialized views that are created based on the following SQL statements: non-aggregated single-table statements, aggregated single-table statements, multi-table join statements, aggregated multi-table join statements, and UNION ALL statements. For SQL statements that do not fall into these five categories, incremental refresh is not supported. For more information about the requirements for incremental refresh, see the Incremental refresh section in Refresh a materialized view.

  Note

  For OceanBase Database V4.3.5, incremental refresh for single-table non-aggregated and `UNION ALL` statements is supported starting from V4.3.5 BP3.

• The REFRESH FAST method uses the records in the materialized view log to determine what needs to be incrementally refreshed. Therefore, when you use incremental refresh to refresh a materialized view, you must create the materialized view log for the base table before you create the materialized view. For more information, see Materialized view log.

  Note

  For V4.3.5, the automatic management of materialized view logs is supported starting from V4.3.5 BP4. If automatic management of materialized view logs is enabled, you do not need to create the materialized view log for the base table before you create an incremental refresh materialized view. OceanBase Database automatically creates the corresponding materialized view log or updates the existing materialized view log table definition to include the columns required by the new materialized view. For more information, see Automatic management of materialized view logs.

• When you create a materialized view, you can add the AS OF PROCTIME() clause to the base table. If you use AS OF PROCTIME() in a location other than the base table, an error is returned.

  • The AS OF PROCTIME() clause specifies to skip the refresh of the table during incremental refresh, thereby accelerating the incremental refresh of the materialized view. You do not need to create a materialized view log for the table specified by AS OF PROCTIME(). If you want to use an alias for the table, you must specify the alias after the AS OF PROCTIME() clause.

    Note

    For OceanBase Database V4.3.5, you can add the AS OF PROCTIME() clause to the base table when you create a materialized view starting from V4.3.5 BP4.

  • When you use a standard view declared as a dimension table (AS OF PROCTIME()) as the base table of an incremental refresh materialized view, the following limitations apply:

    • Not all tables in the materialized view can be dimension tables, just like the base table.

    Note

    For OceanBase Database V4.3.5, you can use a standard view declared as a dimension table (AS OF PROCTIME()) as the base table of an incremental refresh materialized view starting from V4.3.5 BP5.

Here is an example:

1. Create a table named tbl5 as the base table of the materialized view.

   CREATE TABLE tbl5 (col1 INT PRIMARY KEY, col2 INT, col3 INT);
   

2. Create a materialized view log on the tbl5 table. Specify the SEQUENCE option for the materialized view log, which indicates that the changes are identified by sequence numbers. Specify the col2 and col3 columns to be recorded.

   CREATE MATERIALIZED VIEW LOG ON tbl5
       WITH SEQUENCE (col2, col3) INCLUDING NEW VALUES;
   

3. Create a materialized view named mv_tbl5 based on the tbl5 table. Specify the incremental refresh strategy (REFRESH FAST) for the materialized view. In the query part, specify to group the records by the col2 column and calculate the number of records in each group (cnt), the number of non-null records in the col3 column (cnt_col3), and the sum of the col3 column (sum_col3) as the result of the materialized view.

   CREATE MATERIALIZED VIEW mv_tbl5
       REFRESH FAST
       AS SELECT col2, COUNT(*) cnt, COUNT(col3) cnt_col3, SUM(col3) sum_col3
          FROM tbl5
          GROUP BY col2;
   

4. Create a materialized view named mv2_tbl5_tbl1 based on the tbl5 and tbl1 tables. Specify the incremental refresh strategy for the materialized view. Join the tables by using the col1 field. Use AS OF PROCTIME() to specify that the tbl1 table is skipped during the incremental refresh of the materialized view.

   CREATE MATERIALIZED VIEW mv2_tbl5_tbl1
       REFRESH FAST ON DEMAND
       AS SELECT 
           t5.col1 tbl5_c1,
           t1.col1 tbl1_c1,
           t5.col2 tbl5_c2,
           t1.col2 tbl1_c2
       FROM tbl5 t5
           INNER JOIN tbl1 AS OF PROCTIME() t1
           ON t5.col1 = t1.col1
       WHERE t5.col2 = 3;
   

5. Create an incremental refresh materialized view based on a standard view that is declared as a dimension table (AS OF PROCTIME()).

   1. Create a view named v1_tbl5 based on the tbl5 table.

      obclient> CREATE VIEW v1_tbl5 AS SELECT * FROM tbl5;
      

   2. Create a materialized view named mv3_tbl5_v_tbl5 based on the tbl5 and v1_tbl5 tables. Specify the incremental refresh strategy for the materialized view. Join the tables by using the col1 field. Use AS OF PROCTIME() to specify that the v1_tbl5 view is a dimension table.

      obclient> CREATE MATERIALIZED VIEW mv3_tbl5_v_tbl5
          AS SELECT
              a.col1 a_c1,
              b.col1 b_c1
          FROM tbl5 a JOIN v1_tbl5 AS OF PROCTIME() b
          ON a.col1 = b.col1;
      

Create a materialized view with a mixed refresh strategy (default)

When you create a materialized view, you can omit or specify the REFRESH FORCE clause to set the refresh strategy to mixed refresh.

Here is an example:

Create a materialized view named mv_rf_tbl1 based on table tbl1, set the refresh strategy to mixed refresh (REFRESH FORCE), and specify that the data source of the materialized view consists of the col1 and col2 columns of the rows in tbl1 where col3 is greater than or equal to 20.

CREATE MATERIALIZED VIEW mv_rf_tbl1
    REFRESH FORCE
    AS SELECT col1, col2
       FROM tbl1
       WHERE col3 >= 20;

Create a materialized view that never refreshes

When you create a materialized view, you can use the NEVER REFRESH clause to set the refresh strategy to never refresh. This means that the materialized view is only refreshed when it is created and cannot be refreshed again after creation.

Here is an example:

Create a materialized view named mv_nr_tbl1 based on table tbl1, set the refresh strategy to never refresh (NEVER REFRESH), and specify that the data source of the materialized view consists of the col1 and col2 columns of the rows in tbl1 where col3 is greater than or equal to 20.

CREATE MATERIALIZED VIEW mv_nr_tbl1
    NEVER REFRESH
    AS SELECT col1, col2
       FROM tbl1
       WHERE col3 >= 20;

Create a materialized view with an automatic refresh schedule

When you create a materialized view, you can specify the START WITH datetime_expr and NEXT datetime_expr clauses to create a background automatic refresh task for the materialized view.

Here is an example:

Create a materialized view named mv_rc_swn_tbl1 based on the tbl1 table. Set the refresh strategy of the materialized view to complete refresh. Set the initial refresh time to the current date and time, and set the refresh interval to 1 hour.

CREATE MATERIALIZED VIEW mv_rc_swn_tbl1
    REFRESH COMPLETE
        START WITH current_date NEXT current_date + INTERVAL '1' HOUR
    AS SELECT col1, col2
       FROM tbl1
       WHERE col3 >= 20;

References

• DBMS_MVIEW Overview
• Materialized Views Overview
• Materialized Views Log
• Refresh Materialized Views
• Materialized Views Query Rewrite
• Query Materialized Views
• Change Materialized Views
• Delete Materialized Views