建立唯讀分區 - PolarDB

您可以將分區和二級子分區設定為唯讀狀態，用於保護資料不受任何使用者或觸發器執行的DML操作的影響。

唯讀分區如下圖所示：

文法

建立表時建立唯讀分區

CREATE TABLE [IF NOT EXISTS] [schema.]table_name
    table_definition [READ {ONLY | WRITE}]
    partition_options;

其中partition_options為：

PARTITION BY
    { RANGE{(expr) | COLUMNS(column_list)} }
    [(partition_definition [, partition_definition] ...)]

partition_definition為：

    PARTITION partition_name
        [VALUES LESS THAN {expr | MAXVALUE}]
        [READ {ONLY | WRITE}]
        [[STORAGE] ENGINE [=] engine_name]
        [COMMENT [=] 'string' ]
        [DATA DIRECTORY [=] 'data_dir']
        [INDEX DIRECTORY [=] 'index_dir']
        [MAX_ROWS [=] max_number_of_rows]
        [MIN_ROWS [=] min_number_of_rows]
        [TABLESPACE [=] tablespace_name]

修改表時建立唯讀分區

ALTER TABLE tbl_name
    [alter_option [, alter_option] ...]
    [partition_options]

其中partition_options為：

partition_options:
    partition_option [partition_option] ...

partition_option為：

partition_option: {
    ADD PARTITION (partition_definition)

partition_definition為：

    PARTITION partition_name
        [VALUES LESS THAN {expr | MAXVALUE}]
        [READ {ONLY | WRITE}]
        [[STORAGE] ENGINE [=] engine_name]
        [COMMENT [=] 'string' ]
        [DATA DIRECTORY [=] 'data_dir']
        [INDEX DIRECTORY [=] 'index_dir']
        [MAX_ROWS [=] max_number_of_rows]
        [MIN_ROWS [=] min_number_of_rows]
        [TABLESPACE [=] tablespace_name]

其中alter_option為：

alter_option: {
    table_options
  | ADD [COLUMN] col_name column_definition
        [FIRST | AFTER col_name]
  | ADD [COLUMN] (col_name column_definition,...)
  | ADD {INDEX | KEY} [index_name]
        [index_type] (key_part,...) [index_option] ...
  | ADD {FULLTEXT | SPATIAL} [INDEX | KEY] [index_name]
        (key_part,...) [index_option] ...
  | ADD [CONSTRAINT [symbol]] PRIMARY KEY
        [index_type] (key_part,...)
        [index_option] ...
  | ADD [CONSTRAINT [symbol]] UNIQUE [INDEX | KEY]
        [index_name] [index_type] (key_part,...)
        [index_option] ...
  | ADD [CONSTRAINT [symbol]] FOREIGN KEY
        [index_name] (col_name,...)
        reference_definition
  | ADD [CONSTRAINT [symbol]] CHECK (expr) [[NOT] ENFORCED]
  | DROP {CHECK | CONSTRAINT} symbol
  | ALTER {CHECK | CONSTRAINT} symbol [NOT] ENFORCED
  | ALGORITHM [=] {DEFAULT | INSTANT | INPLACE | COPY}
  | ALTER [COLUMN] col_name {
        SET DEFAULT {literal | (expr)}
      | SET {VISIBLE | INVISIBLE}
      | DROP DEFAULT
    }
  | ALTER INDEX index_name {VISIBLE | INVISIBLE}
  | CHANGE [COLUMN] old_col_name new_col_name column_definition
        [FIRST | AFTER col_name]
  | [DEFAULT] CHARACTER SET [=] charset_name [COLLATE [=] collation_name]
  | CONVERT TO CHARACTER SET charset_name [COLLATE collation_name]
  | {DISABLE | ENABLE} KEYS
  | {DISCARD | IMPORT} TABLESPACE
  | DROP [COLUMN] col_name
  | DROP {INDEX | KEY} index_name
  | DROP PRIMARY KEY
  | DROP FOREIGN KEY fk_symbol
  | FORCE
  | LOCK [=] {DEFAULT | NONE | SHARED | EXCLUSIVE}
  | MODIFY [COLUMN] col_name column_definition
        [FIRST | AFTER col_name]
  | ORDER BY col_name [, col_name] ...
  | RENAME COLUMN old_col_name TO new_col_name
  | RENAME {INDEX | KEY} old_index_name TO new_index_name
  | RENAME [TO | AS] new_tbl_name
  | {WITHOUT | WITH} VALIDATION
}

參數

參數名稱	參數說明
table_name	表名稱。
expr	分區欄位運算式。
column_list	分區欄位列表，不支援運算式。
MAXVALUE	最大值。
partition_name	分區名稱，同一個表中不可重複。
engine_name	儲存引擎名稱。
table_options	表選項。
col_name	列名。

注意事項

您不能修改唯讀分區的資料。如果嘗試修改唯讀分區的資料，系統會報錯ERROR HY000: Data in a read-only partition or subpartition cannot be modified.。這裡的修改操作不僅僅包括INSERT、UPDATE和DELETE操作，任何對唯讀分區資料結果產生變化的DDL操作都會被拒絕。

由於添加列不會修改原有的唯讀資料屬性，因此添加列是被允許的。如下：

ALTER TABLE [schema.]table_name ADD col_new varchar(100) DEFAULT 'i am not empty';

樣本

建立t1表時，指定t1表的所有分區為唯讀分區

CREATE TABLE t1 (
  id INT,
  year_col INT
) READ ONLY
PARTITION BY RANGE (year_col) (
  PARTITION p0 VALUES LESS THAN (2001),
  PARTITION p1 VALUES LESS THAN (2010),
  PARTITION p2 VALUES LESS THAN (2020)
);

為t1表新增唯讀分區

ALTER TABLE t1 ADD PARTITION (PARTITION p3 values LESS THAN (2030));
Query OK, 0 rows affected (0.22 sec)
Records: 0  Duplicates: 0  Warnings: 0

新增唯讀分區後，可以發現新分區仍然為唯讀分區

SHOW CREATE TABLE t1;
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| t1    | CREATE TABLE `t1` (
  `id` int(11) DEFAULT NULL,
  `year_col` int(11) DEFAULT NULL
) /*!99990 800020201 READ ONLY */ ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
/*!50100 PARTITION BY RANGE (`year_col`)
(PARTITION p0 VALUES LESS THAN (2001) ENGINE = InnoDB,
 PARTITION p1 VALUES LESS THAN (2010) ENGINE = InnoDB,
 PARTITION p2 VALUES LESS THAN (2020) ENGINE = InnoDB,
 PARTITION p3 VALUES LESS THAN (2030) ENGINE = InnoDB) */ |
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

為t1表建立混合屬性的分區

CREATE TABLE t1 (
    id INT,
    year_col INT
) READ WRITE
PARTITION BY RANGE (year_col) (
    PARTITION p0 VALUES LESS THAN (2001) READ ONLY,
    PARTITION p1 VALUES LESS THAN (2010),
    PARTITION p2 VALUES LESS THAN (2020) READ ONLY
);

如何查看唯讀分區

目前只能通過SHOW CREATE命令查詢分區表的分區唯讀屬性，例如：

show create table t1;
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| t1    | CREATE TABLE `t1` (
  `id` int(11) DEFAULT NULL,
  `year_col` int(11) DEFAULT NULL
) /*!99990 800020201 READ WRITE */ ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
/*!50100 PARTITION BY RANGE (`year_col`)
(PARTITION p0 VALUES LESS THAN (2001) */ /*!99990 800020201  READ ONLY */
/*!50100  ENGINE = InnoDB,
 PARTITION p1 VALUES LESS THAN (2010) ENGINE = InnoDB,
 PARTITION p2 VALUES LESS THAN (2020) */ /*!99990 800020201  READ ONLY */
/*!50100  ENGINE = InnoDB) */ |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)