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] [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]
    }

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/*Only 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/*Only 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 /*Only 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

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 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 with RANGE partitioning and HASH subpartitioning.

  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 the zstd 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
  

• Define a foreign key for the ref_t2 table. When a DELETE operation affects a matching row in a subtable, the value of the primary key in the parent table is set 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 with RANGE + RANGE subpartitioning.

  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 replicated table named dup_t1 at the cluster level. You can insert data and read and write data from a replicated table in the same way as from 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 you are connected to.

  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 table named test_tbl1. The values in the col1 column of the table will auto-increment and the column is set 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 used in various business scenarios in Oracle compatibility mode and ensure basic accuracy and functionality.
• Generally, the purpose of using temporary tables is to maintain compatibility and reduce business modifications. If the business scenarios are limited and the performance requirements for temporary tables are not high, you can use them. 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 any notable advantages.
• When a transaction ends or a session disconnects, additional data cleanup needs to be performed for temporary tables, which causes extra overheads.
• The data check and cleanup performed for temporary tables upon login may put pressure on the login thread, thus lengthening the login time. In severe cases, the login may fail.

Create a temporary table

By default, the database system automatically modifies the table creation statement as follows:

• Adds the SYS_SESSION_ID column as the primary key.
• Adds the SYS_SESS_CREATE_TIME column as a normal column.
• Creates a hash-partitioned table with 16 partitions, using the SYS_SESSION_ID column as the partitioning key.

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 in a temporary table

When you execute the INSERT statement, the database system automatically inserts the session ID of the current session and the creation time of the session into the SYS_SESSION_ID and SYS_SESS_CREATE_TIME columns, respectively.

When you execute the UPDATE, DELETE, or SELECT statement, the database system automatically modifies the SQL statement as follows: adds the filter condition "SYS_SESSION_ID = session ID of the current session" to the statement. With this condition, the SQL optimizer can perform partition pruning and extract the query range.

Data cleanup in a temporary table

• For temporary tables with the ON COMMIT DELETE ROWS option (transaction temporary tables, which is also the default option), when a transaction ends, a new transaction is started to delete the data in the temporary table by executing the DELETE statement.
• For temporary tables with the ON COMMIT PRESERVE ROWS option (session temporary tables), when a session disconnects, the DELETE statement is executed to delete the data in the temporary table.
• Since session IDs can be reused, in OceanBase Database V3.2.4 BP4 and earlier, the data of the current session ID is checked upon login. If additional data cleanup is required, it is performed.
• Data check and cleanup based on non-unique session IDs may cause login failures (cluster unavailable).

Routing of a temporary table

• For transaction temporary tables (ON COMMIT DELETE ROWS) Accesses to the transaction temporary table within a transaction can only be routed to the node where the transaction was started.

• 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 routed only to the current session.

Drop a temporary table

You can successfully execute the DROP statement while executing an DML statement, to delete a temporary table and all its data. This behavior differs from that in 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 using the temporary table, delete the temporary table, or perform a major compaction. Generally, the issue can be resolved on its own. If not, proceed to step 2.
2. Restart the server where the login failure occurred.

PL cache bloat due to plan reusability

For example, a procedure definition statement that contains a temporary table:

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

Accesses to the temporary table by different sessions cannot share a plan. Each session needs to compile the procedure p1 to generate a cache for it. 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;'

Rewriting the SQL statement of the temporary table into a dynamic SQL statement can bypass this issue.

Data not cleared after a failure

In some cases, data may be left after a failure. At present, there is no automatic cleanup method. Generally, this does not affect the use of the temporary table. If a large amount of data is left, you can drop the temporary table and rebuild it.