CREATE TABLE

Description

This statement creates a table in a database.

Syntax

CREATE [GLOBAL TEMPORARY] TABLE table_name
      (table_definition_list) [table_option_list] [partition_option] [on_commit_option]
CREATE [GLOBAL TEMPORARY] TABLE table_name
      (table_definition_list) [table_option_list] [partition_option] [table_column_group_option] [AS] select;

table_definition_list:
    table_definition [, table_definition ...]

table_definition:
      column_definition
     | [,
        | [CONSTRAINT [constraint_name]] { PRIMARY KEY|UNIQUE } (column_name) //Add a constraint after all columns are created.
        | [CONSTRAINT [constraint_name]] FOREIGN KEY (column_name, column_name ...) references_clause constraint_state
        | [CONSTRAINT [constraint_name]] CHECK(expression) constraint_state
       ]

column_definition_list:
    column_definition [, column_definition ...]

column_definition:
    column_name data_type
    [VISIBLE|INVISIBLE] [GENERATED BY DEFAULT AS IDENTITY | GENERATED ALWAYS AS IDENTITY]
    {
    [DEFAULT expression]
    [NULL | NOT NULL]
    [CONSTRAINT [constraint_name]] [ PRIMARY KEY|UNIQUE ]       //Add a constraint when the column is created.
    [CONSTRAINT [constraint_name] CHECK(expression) constraint_state]
    [CONSTRAINT [constraint_name] references_clause]
    |
    [GENERATED ALWAYS] AS (expression) [VIRTUAL]
    [NULL | NOT NULL] [UNIQUE KEY] [[PRIMARY] KEY] [UNIQUE LOWER_KEY] [SKIP_INDEX(skip_index_option_list)]
    }

skip_index_option_list:
    skip_index_option [,skip_index_option ...]

skip_index_option:
    MIN_MAX
    | SUM

references_clause:
     REFERENCES table_name [ (column_name, column_name ...) ] [ON DELETE {SET NULL | CASCADE}]

constraint_state:
    [RELY | NORELY] [USING INDEX index_option_list] [ENABLE | DISABLE] [VALIDATE | NOVALIDATE]

index_option_list:
    index_option [ index_option ...]

index_option:
      [GLOBAL | LOCAL]
    | block_size
    | compression
    | STORING(column_name_list)

table_option_list:
    table_option [ table_option ...]

table_option:
      TABLEGROUP = tablegroup_name
    | block_size
    | compression
    | ENABLE ROW MOVEMENT
    | DISABLE ROW MOVEMENT
    | physical_attribute
    | parallel_clause
    | DUPLICATE_SCOPE [=] 'none|cluster'

physical_attribute_list:
    physical_attribute [physical_attribute]

physical_attribute:
    PCTFREE [=] num
    | PCTUSED num
    | INITRANS num
    | MAXTRANS num
    | STORAGE(storage_option [storage_option] ...)
    | TABLESPACE tablespace

parallel_clause:
    {NOPARALLEL | PARALLEL integer}

compression:
    NOCOMPRESS
    | COMPRESS { BASIC | FOR OLTP | FOR QUERY [LOW | HIGH]  | FOR ARCHIVE [LOW | HIGH]}

storage_option:
    INITIAL num [K|M|G|T|P|E]
    | NEXT num [K|M|G|T|P|E]
    | MINEXTENTS num [K|M|G|T|P|E]
    | MAXEXTENTS num [K|M|G|T|P|E]

partition_option:
      PARTITION BY HASH(column_name_list)
      [subpartition_option] hash_partition_define
    | PARTITION BY RANGE (column_name_list)
      [subpartition_option] (range_partition_list)
    | PARTITION BY LIST (column_name_list)
      [subpartition_option] (list_partition_list)

/*Template-based subpartitioning*/
subpartition_option:
      SUBPARTITION BY HASH (column_name_list) hash_subpartition_define
    | SUBPARTITION BY RANGE (column_name_list) SUBPARTITION TEMPLATE
      (range_subpartition_list)
    | SUBPARTITION BY LIST (column_name_list) SUBPARTITION TEMPLATE
      (list_subpartition_list)

/*Non-template-based subpartitioning*/
subpartition_option:
      SUBPARTITION BY HASH (column_name_list)
    | SUBPARTITION BY RANGE (column_name_list)
    | SUBPARTITION BY LIST (column_name_list)

subpartition_list:
      (hash_subpartition_list)
    | (range_subpartition_list)
    | (list_subpartition_list)

hash_partition_define:
      PARTITIONS partition_count [TABLESPACE tablespace] [compression]
    | (hash_partition_list)

hash_partition_list:
    hash_partition [, hash_partition ...]

hash_partition:
    partition [partition_name] [subpartition_list/*Optional for non-template-based subpartitioning*/]

hash_subpartition_define:
      SUBPARTITIONS subpartition_count
    | SUBPARTITION TEMPLATE (hash_subpartition_list)

hash_subpartition_list:
    hash_subpartition [, hash_subpartition ...]

hash_subpartition:
    subpartition [subpartition_name]

range_partition_list:
    range_partition [, range_partition ...]

range_partition:
    PARTITION [partition_name]
    VALUES LESS THAN {(expression_list) | (MAXVALUE)}
    [subpartition_list/*Optional for non-template-based subpartitioning*/]
    [ID = num] [physical_attribute_list] [compression]

range_subpartition_list:
    range_subpartition [, range_subpartition ...]

range_subpartition:
    SUBPARTITION subpartition_name
    VALUES LESS THAN {(expression_list) | MAXVALUE} [physical_attribute_list]

list_partition_list:
    list_partition [, list_partition] ...

list_partition:
    PARTITION [partition_name]
    VALUES (DEFAULT | expression_list)
    [subpartition_list /*Optional for non-template-based subpartitioning*/]
    [ID num] [physical_attribute_list] [compression]

list_subpartition_list:
    list_subpartition [, list_subpartition] ...

list_subpartition:
    SUBPARTITION [partition_name] VALUES (DEFAULT | expression_list) [physical_attribute_list]

expression_list:
    expression [, expression ...]

column_name_list:
    column_name [, column_name ...]

partition_name_list:
    partition_name [, partition_name ...]

partition_count | subpartition_count:
    INT_VALUE

on_commit_option:
    ON COMMIT DELETE ROWS
  | ON COMMIT PRESERVE ROWS

table_column_group_option:
    WITH COLUMN GROUP(all columns)
  | WITH COLUMN GROUP(each column)
  | WITH COLUMN GROUP(all columns, each column)

Parameter description

Examples

• Create a table named tbl1.

  obclient> CREATE TABLE tbl1 (col1 INT PRIMARY KEY, col2 VARCHAR(50)) ;
  Query OK, 0 rows affected
  

• Create a table partitioned by HASH with 8 partitions.

  obclient> CREATE TABLE tbl4 (col1 INT PRIMARY KEY, col2 INT) PARTITION BY HASH(col1) PARTITIONS 8;
  Query OK, 0 rows affected
  

• Create a table partitioned by RANGE and subpartitioned by HASH.

  obclient> CREATE TABLE tbl5 (col1 INT, col2 INT, col3 INT)
                   PARTITION BY RANGE(col1)
                   SUBPARTITION BY HASH(col2)  SUBPARTITIONS  5
                   (PARTITION p0 VALUES LESS THAN(0),
                    PARTITION p1 VALUES LESS THAN(100));
  Query OK, 0 rows affected
  

• Enable encoding, use zstd as the compression algorithm, and set the macroblock reservation space to 5%.

  obclient> CREATE TABLE tbl6 (col1 INT, col2 INT, col3 VARCHAR(64))
                   COMPRESS FOR ARCHIVE
                   PCTFREE 5;
  Query OK, 0 rows affected
  

• Create a transaction-level temporary table.

  obclient> CREATE GLOBAL TEMPORARY TABLE tbl7(col1 INT) ON COMMIT DELETE ROWS;
  Query OK, 0 rows affected
  

• Create a table with constraints.

  obclient> CREATE TABLE tbl8 (col1 INT, col2 INT, col3 INT,CONSTRAINT equal_check1 CHECK(col2 = col3 * 2) ENABLE VALIDATE);
  Query OK, 0 rows affected
  

• Add a foreign key to the ref_t2 table. When a DELETE operation affects a row that matches a row in a child table, set the key value in the parent table to NULL.

  obclient> CREATE TABLE ref_t1(c1 INT PRIMARY KEY,C2 INT);
  Query OK, 0 rows affected
  
  obclient> CREATE TABLE ref_t2(c1 INT PRIMARY KEY,C2 INT,FOREIGN KEY(c2) REFERENCES ref_t1(c1) ON DELETE SET NULL);
  Query OK, 0 rows affected
  

• Create a table partitioned by RANGE and subpartitioned by RANGE.

  obclient> CREATE TABLE tbl9 (col1 INT, col2 INT, col3 INT)
                   PARTITION BY RANGE(col1)
                   SUBPARTITION BY RANGE(col2)
  (
    PARTITION p0 VALUES LESS THAN(100)
    (
      SUBPARTITION p0_r1 VALUES LESS THAN(2019),
      SUBPARTITION p0_r2 VALUES LESS THAN(2020),
      SUBPARTITION p0_r3 VALUES LESS THAN(2021)
    ),
    PARTITION p1 VALUES LESS THAN(200)
    (
      SUBPARTITION p1_r1 VALUES LESS THAN(2019),
      SUBPARTITION p1_r2 VALUES LESS THAN(2020),
      SUBPARTITION p1_r3 VALUES LESS THAN(2021)
    ),
    PARTITION p2 VALUES LESS THAN(300)
    (
      SUBPARTITION p2_r1 VALUES LESS THAN(2019),
      SUBPARTITION p2_r2 VALUES LESS THAN(2020),
      SUBPARTITION p2_r3 VALUES LESS THAN(2021)
    )
  );
  Query OK, 0 rows affected
  

• Create the tbl10 table with a DOP of 3.

  obclient> CREATE TABLE tbl10(col1 INT PRIMARY KEY, col2 INT) PARALLEL 3;
  Query OK, 0 rows affected
  

• Set the default value of a column based on a function.

  obclient> CREATE SEQUENCE SEQ_PERSONIPTVSEQ START WITH 1 MINVALUE 1 MAXVALUE 10 INCREMENT BY 2 NOCYCLE NOORDER CACHE 30;
  Query OK, 0 rows affected
  
  obclient> SELECT LPAD(SEQ_PERSONIPTVSEQ.NEXTVAL,18,TO_CHAR(SYSDATE,'YYYY-MM-DD HH24:MI:SS')) FROM DUAL;
  +----------------------------------------------------------------------------+
  | LPAD(SEQ_PERSONIPTVSEQ.NEXTVAL,18,TO_CHAR(SYSDATE,'YYYY-MM-DDHH24:MI:SS')) |
  +----------------------------------------------------------------------------+
  | 2022-07-05 11:34:1                                                         |
  +----------------------------------------------------------------------------+
  1 row in set
  
  obclient> CREATE TABLE FUNC_DEFAULT_TEST ( OID NUMBER(20,0) DEFAULT LPAD(SEQ_PERSONIPTVSEQ.NEXTVAL,18,TO_CHAR(SYSDATE,'YYYY-MM-DD HH24:MI:SS')) NOT NULL);
  Query OK, 0 rows affected
  

• Create a replica-level copy table named dup_t1. You can insert data and read and write data from and to the replica-level copy table as you would with a normal table. For a read request, if you use a Proxy, the request can be routed to any OBServer node; if you directly connect to an OBServer node and the local replica is available, the read request is processed on the OBServer node.

  obclient> CREATE TABLE dup_t1(c1 int) DUPLICATE_SCOPE = 'cluster';
  Query OK, 0 rows affected
  
  obclient> INSERT INTO dup_t1 VALUES(1);
  Query OK, 1 row affected
  
  obclient> SELECT * FROM dup_t1;
  +------+
  | c1   |
  +------+
  |    1 |
  +------+
  1 row in set
  

• Create a columnstore table named tbl1_cg.

  CREATE TABLE tbl1_cg (col1 NUMBER PRIMARY KEY, col2 VARCHAR2(50)) WITH COLUMN GROUP(each column);
  

• Specify the Skip Index attribute for a column when creating a table.

  CREATE TABLE test_skidx(
    col1 NUMBER SKIP_INDEX(MIN_MAX, SUM),
    col2 FLOAT SKIP_INDEX(MIN_MAX),
    col3 VARCHAR2(1024) SKIP_INDEX(MIN_MAX),
    col4 CHAR(10)
  );
  

• Create a table named test_tbl1, set the col1 column to an auto-increment column, and set it as the primary key.

  CREATE TABLE test_tbl1 (
    col1 INT GENERATED BY DEFAULT AS IDENTITY,
    col2 VARCHAR2(50),
    PRIMARY KEY (col1)
  );  
  

Limitations on global temporary tables in Oracle compatibility mode

• Temporary tables are widely used in various business scenarios in Oracle compatibility mode, ensuring basic accuracy and functionality.
• Temporary tables are generally used for compatibility and to reduce the amount of business modification. If the business scenarios are limited and the performance requirements for temporary tables are not high, you can use temporary tables. It is better to convert the business scenarios to use regular tables.

Performance and stability

• The SQL execution efficiency of temporary tables is similar to that of normal tables, without notable advantages.
• When a transaction is completed or a session is disconnected, additional work, such as data cleanup, needs to be performed for temporary tables, which causes additional overheads.
• The checks and cleanups performed on temporary tables upon login may put pressure on the login thread, causing login delays. In severe cases, the login may fail.

Create a temporary table

When a temporary table is created, the system automatically modifies the table creation statement:

• It adds a SYS_SESSION_ID column as the primary key.
• It adds a SYS_SESS_CREATE_TIME column as a regular column.
• It creates a hash-partitioned table that uses SYS_SESSION_ID as the partitioning key with 16 partitions.

For example:

CREATE GLOBAL TEMPORARY TABLE t1(
  c1 INT,
  c2 INT,
  PRIMARY KEY(c1)
);

is automatically modified into the following statement.

CREATE GLOBAL TEMPORARY TABLE t1(
  SYS_SESSION_ID INT,
  SYS_SESS_CREATE_TIME INT,
  c1 INT,
  c2 INT,
  PRIMARY KEY(SYS_SESSION_ID, c1)
)
PARTITION BY HASH(SYS_SESSION_ID) PARTITIONS 16;

DML/Query statements for temporary tables

When the INSERT operation is performed, the current session's session ID and session creation time are default inserted into the SYS_SESSION_ID and SYS_SESS_CREATE_TIME columns.

For the UPDATE, DELETE, and SELECT operations, the system automatically modifies the SQL statement by adding the filter condition "SYS_SESSION_ID = session ID of the current session" to the statement. This condition enables the SQL optimizer to perform partition pruning and retrieve the data within the query range.

Data cleanup for temporary tables

• For temporary tables with the ON COMMIT DELETE ROWS option (transaction temporary tables, which is also the default option), after a transaction is completed, a new transaction is started to execute the DELETE statement to delete the data in the temporary table.
• For temporary tables with the ON COMMIT PRESERVE ROWS option (session temporary tables), when a session is disconnected, the DELETE statement is executed to delete the data in the temporary table.
• If session IDs are reused, in OceanBase Database V3.2.4 BP4 and earlier, the system checks the data of the current session ID upon login and performs a cleanup if necessary.
• The login check and cleanup based on non-unique session IDs may cause login failures (cluster unavailable).

Routing of queries to temporary tables

• For transaction temporary tables (ON COMMIT DELETE ROWS) Accesses to the transaction temporary table can only be routed to the node where the transaction is initiated.

• For session temporary tables (ON COMMIT PRESERVE ROWS) After a session accesses a temporary table, the OBServer node notifies the Proxy to allow subsequent requests from the Proxy to be sent only to the current session.

Drop a temporary table

You can successfully execute the DROP statement while performing DML operations, and all data in the temporary table will be deleted. This is different from Oracle, where you must wait until all sessions no longer hold resources of the temporary table before you can execute the DROP statement.

Cross-version support

Workarounds for severe issues

Unable to log in

1. Stop the business related to temporary tables, delete temporary tables, or perform a major compaction. Generally, the issue can be resolved. If not, proceed to step 2.
2. Restart the server where the login fails.

PL cache bloat due to plan reusability

For example, a temporary table is included in the PL definition:

CREATE PROCEDUCE p1 () (
  INSERT INTO temp_table VALUES (xxx);
  SELECT * FROM temp_table WHERE ROWNUM = 1 INTO var1;
);

Different sessions cannot share a plan for accessing the temporary table, so each session needs to compile the p1 procedure to generate a cache. This may lead to stability issues. You can rewrite the SQL statement as follows:

EXCUTE IMMEDIATE 'SELECT * FROM temp_table WHERE ROWNUM = 1 INTO var1;'

You can rewrite the temporary table SQL statement into a dynamic SQL statement to bypass this issue.

Data not cleared after a failure

A failure may cause data residue. At present, there is no automatic cleanup method. Generally, this does not affect the use of temporary tables. If a large amount of data is residue, you can drop the temporary table and recreate it.