CREATE TABLE PARTITION¶
Function¶
CREATE TABLE PARTITION creates a partitioned table. Partitioned table: refers to splitting what is logically one large table into smaller physical pieces based on specific schemes. The table based on the logic is called a partitioned cable, and a physical piece is called a partition. Data is stored on these smaller physical pieces, namely, partitions, instead of the larger logical partitioned table.
Common partitioning policies include range partitioning, hash partitioning, list partitioning, and value partitioning.
In range partitioning, the table is partitioned into ranges defined by a key column or set of columns, with no overlap between the ranges of values assigned to different partitions. Each range has a dedicated partition for data storage.
Range partitioning maps data to partitions based on ranges of values of the partitioning key that you establish for each partition. This is the most commonly used partitioning policy. Currently, range partitioning only allows the use of the range partitioning policy.
List partitioning allocates records to partitions based on the key values in each partition. The key values do not overlap in different partitions. Create a partition for each group of key values to store corresponding data.
Range partitioning policy: Data is mapped to a created partition based on the partition key value. If the data can be mapped to, it is inserted into the specific partition; if it cannot be mapped to, error messages are returned.
In common partitioning policies, a data distribution range is defined based on one or more columns, and each partition carries data of a range. These columns are called partition keys.
Note
Currently, row-store tables and column-store tables support only range partitioning and list partitioning.
List partitioning is supported only by clusters of 8.1.3 and later versions.
Advantages of Partitioning¶
The performance of some types of queries can be greatly improved, especially when rows with high access rates in a table are located in a single partition or a few partitions. Partitioning narrows the range of data search and improves data access efficiency.
When queries or updates access a large percentage of a single partition, performance can be improved by taking advantage of sequential scan of that partition instead of reads scattered across the whole table.
Bulk loads and deletion can be performed by adding or removing partitions, if that requirement is planned into the partitioning design. It also entirely avoids the VACUUM overhead caused by a bulk DELETE (only for range partitioning).
Precautions¶
A partitioned table supports unique and primary key constraints. The constraint keys of these constraints contain all partition keys.
Syntax¶
CREATE TABLE [ IF NOT EXISTS ] partition_table_name
( [
{ column_name data_type [ COLLATE collation ] [ column_constraint [ ... ] ]
| table_constraint
| LIKE source_table [ like_option [...] ] }[, ... ]
] )
[ WITH ( {storage_parameter = value} [, ... ] ) ]
[ COMPRESS | NOCOMPRESS ]
[ DISTRIBUTE BY { REPLICATION | ROUNDROBIN | { [ HASH ] ( column_name ) } } ]
[ TO { GROUP groupname | NODE ( nodename [, ... ] ) } ]
PARTITION BY {
{VALUES (partition_key)} |
{RANGE (partition_key) ( partition_less_than_item [, ... ] )} |
{RANGE (partition_key) ( partition_start_end_item [, ... ] )} |
{LIST (partition_key) (list_partition_item [, ...])}
} [ { ENABLE | DISABLE } ROW MOVEMENT ];
column_constraint is as follows:
[ CONSTRAINT constraint_name ] { NOT NULL | NULL | CHECK ( expression ) | DEFAULT default_expr | UNIQUE [ NULLS [NOT] DISTINCT | NULLS IGNORE ] index_parameters | PRIMARY KEY index_parameters } [ DEFERRABLE | NOT DEFERRABLE | INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
table_constraint is as follows:
[ CONSTRAINT constraint_name ] { CHECK ( expression ) | UNIQUE [ NULLS [NOT] DISTINCT | NULLS IGNORE ] ( column_name [, ... ] ) index_parameters | PRIMARY KEY ( column_name [, ... ] ) index_parameters} [ DEFERRABLE | NOT DEFERRABLE | INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
like_option is as follows:
{ INCLUDING | EXCLUDING } { DEFAULTS | CONSTRAINTS | INDEXES | STORAGE | COMMENTS | RELOPTIONS | DISTRIBUTION | ALL }
index_parameters is as follows:
[ WITH ( {storage_parameter = value} [, ... ] ) ]
partition_less_than_item is as follows:
PARTITION partition_name VALUES LESS THAN ( { partition_value | MAXVALUE } )
partition_start_end_item is as follows:
PARTITION partition_name { {START(partition_value) END (partition_value) EVERY (interval_value)} | {START(partition_value) END ({partition_value | MAXVALUE})} | {START(partition_value)} | {END({partition_value | MAXVALUE})} }
list_partition_item:
PARTITION partition_name VALUES ( { (partition_value) [, ...] | DEFAULT } )
Parameter Description¶
IF NOT EXISTS
Does not throw an error if a table with the same name exists. A notice is issued in this case.
partition_table_name
Name of the partitioned table
Value range: a string. It must comply with the naming convention.
column_name
Specifies the name of a column to be created in the new table.
Value range: a string. It must comply with the naming convention.
data_type
Specifies the data type of the column.
COLLATE collation
Assigns a collation to the column (which must be of a collatable data type). If no collation is specified, the default collation is used.
The collatable types are char, varchar, text, nchar, and nvarchar.
CONSTRAINT constraint_name
Specifies a name for a column or table constraint. The optional constraint clauses specify constraints that new or updated rows must satisfy for an insert or update operation to succeed.
There are two ways to define constraints:
A column constraint is defined as part of a column definition, and it is bound to a particular column.
A table constraint is not bound to any particular columns but can apply to more than one column.
LIKE source_table [ like_option ... ]
Specifies a table from which the new table automatically copies all column names, their data types, and their not-null constraints.
Unlike INHERITS, the new table and original table are decoupled after creation is complete. Changes to the original table will not be applied to the new table, and it is not possible to include data of the new table in scans of the original table.
Default expressions for the copied column definitions will only be copied if INCLUDING DEFAULTS is specified. The default behavior is to exclude default expressions, resulting in the copied columns in the new table having default values NULL.
NOT NULL constraints are always copied to the new table. CHECK constraints will only be copied if INCLUDING CONSTRAINTS is specified; other types of constraints will never be copied. These rules also apply to column constraints and table constraints.
Columns and constraints copied by LIKE are not merged with the same name. If the same name is specified explicitly or in another LIKE clause, an error is reported.
Any indexes on the source table will not be created on the new table, unless the INCLUDING INDEXES clause is specified.
STORAGE settings for the copied column definitions will only be copied if INCLUDING STORAGE is specified. The default behavior is to exclude STORAGE settings.
Comments for the copied columns, constraints, and indexes will only be copied if INCLUDING COMMENTS is specified. The default behavior is to exclude comments.
If INCLUDING RELOPTIONS is specified, the new table will copy the storage parameter (WITH clause of the source table) of the source table. The default behavior is to exclude partition definition of the storage parameter of the source table.
If INCLUDING DISTRIBUTION is specified, the new table will copy the distribution information of the source table, including distribution type and column, and the new table cannot use DISTRIBUTE BY clause. The default behavior is to exclude distribution information of the source table.
INCLUDING ALL is an abbreviated form of INCLUDING DEFAULTS INCLUDING CONSTRAINTS INCLUDING INDEXES INCLUDING STORAGE INCLUDING COMMENTS INCLUDING RELOPTIONS INCLUDING DISTRIBUTION.
WITH ( storage_parameter [= value] [, ... ] )
Specifies an optional storage parameter for a table or an index. Optional parameters are as follows:
FILLFACTOR
The fillfactor of a table is a percentage between 10 and 100. 100 (complete packing) is the default value. When a smaller fillfactor is specified, INSERT operations pack table pages only to the indicated percentage. The remaining space on each page is reserved for updating rows on that page. This gives UPDATE a chance to place the updated copy of a row on the same page, which is more efficient than placing it on a different page. For a table whose records are never updated, setting the fillfactor to 100 (complete packing) is the appropriate choice, but in heavily updated tables smaller fillfactors are appropriate. The parameter has no meaning for column-store tables.
Value range: 10-100
ORIENTATION
Determines the storage mode of the data in the table.
Valid value:
COLUMN: The data will be stored in columns.
ROW (default value): The data will be stored in rows.
ORC: The data of the table will be stored in ORC format (only HDFS table).
Important
orientation cannot be modified.
COMPRESSION
The valid values for column-store tables are YES/NO and LOW/MIDDLE/HIGH, and the default is LOW.
Note
Currently, row-store table compression is not supported.
MAX_BATCHROW
Specifies the maximum of a storage unit during data loading process. The parameter is only valid for column-store tables.
Value range: 10000 to 60000
Default value: 60000
PARTIAL_CLUSTER_ROWS
Specifies the number of records to be partial cluster stored during data loading process. The parameter is only valid for column-store tables.
Value range: The valid value is no less than 100000. The value is the multiple of MAX_BATCHROW.
enable_delta
Specifies whether to enable delta tables in column-store tables. The parameter is only valid for column-store tables.
Default value: off
DELTAROW_THRESHOLD
A reserved parameter. The parameter is only valid for column-store tables.
The value ranges from 0 to 60000. The default value is 6000.
COLD_TABLECPACE
Specifies the OBS tablespace for the cold partitions in a multi-temperature table. This parameter is available only to partitioned column-store tables and cannot be modified. It must be used together with storage_policy. The parameter STORAGE_POLICY can be left unconfigured. In this case, the default value default_obs_tbs is used.
Valid value: a valid OBS tablespace name
STORAGE_POLICY
Specifies the rule for switching between hot and cold partitions. This parameter is used only for multi-temperature tables. It must be used together with cold_tablespace.
Value range: Cold and hot switchover policy name:Cold and hot switchover threshold. Currently, only LMT and HPN policies are supported. LMT indicates that the switchover is performed based on the last update time of partitions. HPN indicates the switchover is performed based on a fixed number of reserved hot partitions.
LMT:[day]: Switch the hot partition data that is not updated in the last [day] days to the OBS tablespace as cold partition data. [day] is an integer ranging from 0 to 36500, in days.
HPN:[hot_partition_num]: [hot_partition_num] indicates the number of hot partitions (with data) to be retained. The rule is to find the maximum sequence ID of the partitions with data. The partitions without data whose sequence ID is greater than the maximum sequence ID are hot partitions, and [hot_partition_num] partitions are retained as hot partitions in descending order according to the sequence ID. A partition whose sequence ID is smaller than the minimum sequence ID of the retained hot partition is a cold partition. During hot and cold partition switchover, data needs to be migrated to the OBS tablespace. [hot_partition_num] is an integer ranging from 0 to 1600.
Important
The hybrid data warehouse (standalone) does not support cold and hot partition switchover.
For a LIST partition, you are advised to use the HPN policy with caution. Otherwise, the new partition may not be a hot partition.
PERIOD
Specifies the period of automatically creating partitions and enables the automatic partition creation function. Only row-store and column-store range partitioned tables, time series tables, and cold and hot tables are supported. The partition key must be unique and its type can only be TIMESTAMP[(p)] [WITHOUT TIME ZONE], TIMESTAMP[(p)] [WITH TIME ZONE] or DATE. maxvalue partitions are not supported. The value of (nowTime - boundaryTime)/PERIOD must be less than the upper limit of the number of partitions, where nowTime indicates the current time and boundaryTime indicates the earliest partition boundary time. It cannot be used on midrange computers, acceleration clusters, or single-node clusters.
Value range: 1 hour ~ 100 years
Important
In a database compatible with Teradata or MySQL, if the partition key type is DATE, PERIOD cannot be less than 1 day.
If PERIOD is set when a partitioned table is created, you can specify only the partition key. Two default partitions are created during table creation. The time ranges of the two default partitions are both PERIOD. The boundary time of the first default partition is the first hour, day, week, month, or year past the current time. The time unit is selected based on the maximum unit of PERIOD. The boundary time of the second default partition is the boundary time of the first partition plus PERIOD. Assume that the current time is 2022-02-17 16:32:45, and the boundary of the first default partition is described in Table 1.
For more information about the default partitions, see Example 8.
The hybrid data warehouse (standalone) does not support automatic partition creation.
Table 1 Partition boundaries¶ period
Maximum PERIOD Unit
Boundary of First Default Partition
1hour
Hour
2022-02-17 17:00:00
1day
Day
2022-02-18 00:00:00
1month
Month
2022-03-01 00:00:00
13month
Year
2023-01-01 00:00:00
TTL
Specifies the partition expiration time in partition management and enables the automatic partition deletion function. This parameter cannot be set separately. You must set PERIOD in advance or at the same time. The value of this parameter must be greater than or equal to that of PERIOD.
Value range: 1 hour ~ 100 years
Note
PERIOD indicates that data is partitioned by time period. The partition size may affect the query performance. The proc_add_partition (relname regclass, boundaries_interval interval) function is automatically invoked to create a partition after each period. Time To Live (TTL) specifies the data storage period of the table. The data that exceeds the TTL period will be cleared. To do this, the proc_drop_partition (relname regclass, older_than interval) function is automatically invoked based on the period. The PERIOD and TTL values are of the Interval type, for example, 1 hour, 1 day, 1 week, 1 month, 1 year, and 1 month 2 day 3 hour.
The hybrid data warehouse (standalone) does not support automatic partition deletion.
COLVERSION
Specifies the version of the column-store format. Switching between different storage formats is supported. However, the storage format of a partitioned table cannot be switched.
Valid value:
1.0: Each column in a column-store table is stored in a separate file. The file name is relfilenode.C1.0, relfilenode.C2.0, relfilenode.C3.0, or similar.
2.0: All columns of a column-store table are combined and stored in a file. The file is named relfilenode.C1.0.
Default value: 2.0
The value of COLVERSION can only be set to 2.0 for OBS multi-temperature tables.
Note
When creating a column-store table, set COLVERSION to 2.0. Compared with the 1.0 storage format, the performance is significantly improved:
The time required for creating a column-store wide table is significantly reduced.
In the Roach data backup scenario, the backup time is significantly reduced.
The build and catch up time is greatly reduced.
The occupied disk space decreases significantly.
SKIP_FPI_HINT
Indicates whether to skip the hint bits operation when the full-page writes (FPW) log needs to be written during sequential scanning.
Default value: false
Note
If SKIP_FPI_HINT is set to true and the checkpoint operation is performed on a table, no Xlog will be generated when the table is sequentially scanned. This applies to intermediate tables that are queried less frequently, reducing the size of Xlogs and improving query performance.
COMPRESS / NOCOMPRESS
Specifies the keyword COMPRESS during the creation of a table, so that the compression feature is triggered in the case of a bulk INSERT operation. If this feature is enabled, a scan is performed for all tuple data within the page to generate a dictionary and then the tuple data is compressed and stored. If NOCOMPRESS is specified, the table is not compressed.
Default value: NOCOMPRESS, tuple data is not compressed before storage.
DISTRIBUTE BY
Specifies how the table is distributed or replicated between DNs.
Valid value:
REPLICATION: Each row in the table exists on all DNs, that is, each DN has complete table data.
ROUNDROBIN: Each row in the table is sent to each DN in turn. Therefore, data is evenly distributed on each DN. This value is supported only in 8.1.2 or later.
HASH (column_name): Each row of the table will be placed into all the DNs based on the hash value of the specified column.
Important
When DISTRIBUTE BY HASH (column_name) is specified, the primary key and its unique index must contain the column_name column.
When DISTRIBUTE BY HASH (column_name) in a referenced table is specified, the foreign key of the reference table must contain the column_name column.
Default value: determined by the GUC parameter default_distribution_mode
When default_distribution_mode is set to roundrobin, the default value of DISTRIBUTE BY is selected according to the following rules:
If the primary key or unique constraint is included during table creation, hash distribution is selected. The distribution column is the column corresponding to the primary key or unique constraint.
If the primary key or unique constraint is not included during table creation, round-robin distribution is selected.
When default_distribution_mode is set to hash, the default value of DISTRIBUTE BY is selected according to the following rules:
If the primary key or unique constraint is included during table creation, hash distribution is selected. The distribution column is the column corresponding to the primary key or unique constraint.
If the primary key or unique constraint is not included during table creation but there are columns whose data types can be used as distribution columns, hash distribution is selected. The distribution column is the first column whose data type can be used as a distribution column.
If the primary key or unique constraint is not included during table creation and no column whose data type can be used as a distribution column exists, round-robin distribution is selected.
The following data types can be used as distribution columns:
Integer types: TINYINT, SMALLINT, INT, BIGINT, and NUMERIC/DECIMAL
Character types: CHAR, BPCHAR, VARCHAR, VARCHAR2, NVARCHAR2, and TEXT
Date/time types: DATE, TIME, TIMETZ, TIMESTAMP, TIMESTAMPTZ, INTERVAL, and SMALLDATETIME
TO { GROUP groupname | NODE ( nodename [, ... ] ) }
TO GROUP specifies the Node Group in which the table is created. Currently, it cannot be used for HDFS tables. TO NODE is used for internal scale-out tools.
PARTITION BY RANGE(partition_key)
The syntax specifying range partitioning. partition_key indicates the name of a partition key.
Assume that the VALUES LESS THAN syntax is used.
Important
In this case, a maximum of four partition keys are supported, and the partition key must be a column name. If there are multiple partition keys, a column name can appear only once, and two adjacent partition keys must be separated by a comma (,).
Data types supported by the partition keys are as follows: SMALLINT, INTEGER, BIGINT, DECIMAL, NUMERIC, REAL, DOUBLE PRECISION, CHARACTER VARYING(n), VARCHAR(n), CHARACTER(n), CHAR(n), CHARACTER, CHAR, TEXT, NVARCHAR2, NAME, TIMESTAMP[(p)] [WITHOUT TIME ZONE], TIMESTAMP[(p)] [WITH TIME ZONE], and DATE.
Assume that the START END syntax is used.
Important
In this case, only one partition key is supported.
Data types supported by the partition key are as follows: SMALLINT, INTEGER, BIGINT, DECIMAL, NUMERIC, REAL, DOUBLE PRECISION, TIMESTAMP[(p)] [WITHOUT TIME ZONE], TIMESTAMP[(p)] [WITH TIME ZONE], and DATE.
PARTITION BY LIST (partition_key,[...])
The syntax specifying list partitioning. partition_key indicates the name of a partition key.
Important
In list partitioning, a partition key has a maximum of four columns.
In list partitioning, the partition key supports the following data types: TINYINT, SMALLINT, INTEGER, BIGINT, NUMERIC/DECIMAL, TEXT, NVARCHAR2, VARCHAR(n), CHAR, BPCHAR, TIME, TIME WITH TIMEZONE, TIMESTAMP, TIMESTAMP WITH TIME ZONE, DATE, INTERVAL and SMALLDATETIME.
partition_less_than_item
PARTITION partition_name VALUES LESS THAN ( { partition_value | DEFAULT } )
Partition definition syntax in range partitioning. partition_name is the name of a range partition. partition_value is the upper limit of range partition, and the value depends on the type of partition_key. MAXVALUE can specify the upper boundary of a range partition, and it is commonly used to specify the upper boundary of the last range partition.
Important
Upper boundaries must be specified for each partition.
The types of upper boundaries must be the same as those of partition keys.
In a partition list, partitions are arranged in ascending order of upper boundary values. Therefore, a partition with a certain upper boundary value is placed before another partition with a larger upper boundary value.
If a partition key consists of multiple columns, the columns are used for partitioning in sequence. The first column is preferred to be used for partitioning. If the values of the first columns are the same, the second column is used. The subsequent columns are used in the same manner.
partition_start_end_item
PARTITION partition_name {START (partition_value) END (partition_value) EVERY (interval_value)} | {START (partition_value) END (partition_value|MAXVALUE)} | {START(partition_value)} | {END (partition_value| MAXVALUE)}
The syntax of using the start value and interval value to define a range partition. The parameters are described as follows:
partition_name: name or name prefix of a range partition. It is the name prefix only in the following cases (assuming that partition_name is p1):
Using START+END+EVERY will result in partition names such as p1_1, p1_2, and the like. For example, if PARTITION p1 START(1) END(4) EVERY(1) is defined, the generated partitions are [1, 2), [2, 3), and [3, 4), and their names are p1_1, p1_2, and p1_3. In this case, p1 is a name prefix.
If the defined statement is in the first place and has START specified, the range (MINVALUE, START) will be automatically used as the first actual partition, and its name will be p1_0. The other partitions are then named p1_1, p1_2, and the like. For example, if PARTITION p1 START(1), PARTITION p2 START(2) is defined, generated partitions are (MINVALUE, 1), [1, 2), and [2, MAXVALUE), and their names will be p1_0, p1_1, and p2. In this case, p1 is a name prefix and p2 is a partition name. MINVALUE means the minimum value.
partition_value: start point value or end point value of a range partition. The value depends on partition_key and cannot be MAXVALUE.
interval_value: width of each partition for dividing the [START, END) range. It cannot be MAXVALUE. If the value of (END - START) divided by EVERY has a remainder, the width of only the last partition is less than the value of EVERY.
MAXVALUE: maximum value. It is usually used to set the upper boundary for the last range partition.
Important
If the defined statement is in the first place and has START specified, the range (MINVALUE, START) will be automatically used as the first actual partition.
The START END syntax must comply with the following rules:
The value of START (if any, same for the following situations) in each partition_start_end_item must be smaller than that of END.
In two adjacent partition_start_end_item statements, the value of the first END must be equal to that of the second START.
The value of EVERY in each partition_start_end_item must be a positive number (in ascending order) and must be smaller than END minus START.
Each partition includes the start value (unless it is MINVALUE) and excludes the end value. The format is as follows: [Start value, end value).
Partitions created by the same partition_start_end_item belong to the same tablespace.
If partition_name is a name prefix of a partition, the length must not exceed 57 bytes. If there are more than 57 bytes, the prefix will be automatically truncated.
When creating or modifying a partitioned table, ensure that the total number of partitions in the table does not exceed the maximum value (32767).
In statements for creating partitioned tables, START END and LESS THAN cannot be used together.
The START END syntax in a partitioned table creation SQL statement will be replaced with the VALUES LESS THAN syntax when gs_dump is executed.
list_partition_item
PARTITION partition_name VALUES ( { (partition_value) [, ... ] | DEFAULT } )
Partition definition syntax in list partitioning. partition_name indicates the partition name. partition_value is an enumerated value of the list partition boundary. The value depends on the type of partition_key. DEFAULT indicates the default partition boundary.
Important
The following conventions and constraints apply to list partitioned tables:
The partition whose boundary value is DEFAULT is the default partition.
Each list partitioned table can have only one DEFAULT partition.
The number of partitions in a partitioned table cannot exceed 32767, and the number of boundary values of all partitions cannot exceed 32767.
Regardless of the number of partition keys, the boundary of the DEFAULT partition can only be DEFAULT.
If a partition key consists of multiple columns, each partition_value must contain the values of all partition keys. If a partition key contains only one column, the parentheses on both sides of partition_value can be omitted. For details, see Example 4: Creating a List Partition.
If the partition key consists of multiple columns, compare the values in the columns one by one. If a value is different from another value, regardless of their columns, they are different values.
Each value of partition_value must be unique.
When data is inserted, if its partition key and value falls into the boundary of a non-DEFAULT partition, the data is written to the partition. Otherwise, the data is written to the DEFAULT partition.
{ ENABLE | DISABLE } ROW MOVEMENT
Specifies the row movement switch.
If the tuple value is updated on the partition key during the UPDATE action, the partition where the tuple is located is altered. Setting of this parameter enables error messages to be reported or movement of the tuple between partitions.
Valid value:
ENABLE: Row movement is enabled.
DISABLE (default value): Disable row movement.
NOT NULL
Indicates that the column is not allowed to contain NULL values. ENABLE can be omitted.
NULL
Indicates that the column is allowed to contain NULL values. This is the default setting.
This clause is only provided for compatibility with non-standard SQL databases. You are advised not to use this clause.
CHECK (condition) [ NO INHERIT ]
Specifies an expression producing a Boolean result which new or updated rows must satisfy for an insert or update operation to succeed. Expressions evaluating to TRUE or UNKNOWN succeed. If any row of an insert or update operation produces a FALSE result, an error exception is raised and the insert or update does not alter the database.
A check constraint specified as a column constraint should reference only the column's values, while an expression appearing in a table constraint can reference multiple columns.
A constraint marked with NO INHERIT will not propagate to child tables.
ENABLE can be omitted.
DEFAULT default_expr
Assigns a default data value for a column. The value can be any variable-free expressions (Subqueries and cross-references to other columns in the current table are not allowed). The data type of the default expression must match the data type of the column.
The default expression will be used in any insert operation that does not specify a value for the column. If there is no default value for a column, then the default value is NULL.
UNIQUE [ NULLS [NOT] DISTINCT | NULLS IGNORE ] index_parameters
UNIQUE [ NULLS [NOT] DISTINCT | NULLS IGNORE ] ( column_name [, ... ] ) index_parameters
Specifies that a group of one or more columns of a table can contain only unique values.
The [ NULLS [ NOT ] DISTINCT | NULLS IGNORE ] field is used to specify how to process null values in the index column of the Unique index.
Default value: NULL can be inserted repeatedly.
When the inserted data is compared with the original data in the table, the NULL value can be processed in any of the following ways:
NULLS DISTINCT: NULL values are unequal and can be inserted repeatedly.
NULLS NOT DISTINCT: NULL values are equal. If all index columns are NULL, NULL values cannot be inserted repeatedly. If some index columns are NULL, data can be inserted only when non-null values are different.
NULLS IGNORE: NULL values are skipped during the equivalent comparison. If all index columns are NULL, NULL values can be inserted repeatedly. If some index columns are NULL, data can be inserted only when non-null values are different.
The following table lists the behaviors of the three processing modes.
Table 2 Processing of NULL values in index columns in unique indexes¶ Constraint
All Index Columns Are NULL
Some Index Columns Are NULL
NULLS DISTINCT
Can be inserted repeatedly.
Can be inserted repeatedly.
NULLS NOT DISTINCT
Cannot be inserted repeatedly.
Cannot be inserted if the non-null values are equal. Can be inserted if the non-null values are not equal.
NULLS IGNORE
Can be inserted repeatedly.
Cannot be inserted if the non-null values are equal. Can be inserted if the non-null values are not equal.
Note
If DISTRIBUTE BY REPLICATION is not specified, the column table that contains only unique values must contain distribution columns.
PRIMARY KEY index_parameters
PRIMARY KEY ( column_name [, ... ] ) index_parameters
Specifies the primary key constraint specifies that a column or columns of a table can contain only unique (non-duplicate) and non-null values.
Only one primary key can be specified for a table.
Note
If DISTRIBUTE BY REPLICATION is not specified, the column set with a primary key constraint must contain distributed columns.
DEFERRABLE | NOT DEFERRABLE
Controls whether the constraint can be deferred. A constraint that is not deferrable will be checked immediately after every command. Checking of constraints that are deferrable can be postponed until the end of the transaction using the SET CONSTRAINTS command. NOT DEFERRABLE is the default value. Currently, only UNIQUE and PRIMARY KEY constraints of row-store tables accept this clause. All the other constraints are not deferrable.
INITIALLY IMMEDIATE | INITIALLY DEFERRED
If a constraint is deferrable, this clause specifies the default time to check the constraint.
If the constraint is INITIALLY IMMEDIATE (default value), it is checked after each statement.
If the constraint is INITIALLY DEFERRED, it is checked only at the end of the transaction.
The constraint check time can be altered using the SET CONSTRAINTS command.
Examples¶
Example 1: Use the LESS THAN syntax to create a range partitioned table.
The range partitioned table customer_address has four partitions and their partition keys are of the integer type. The ranges of the partitions are as follows: ca_address_sk < 2450815, 2450815 <= ca_address_sk < 2451179, 2451179 <= ca_address_sk < 2451544, 2451544 <= ca_address_sk.
CREATE TABLE customer_address ( ca_address_sk INTEGER NOT NULL , ca_address_id CHARACTER(16) NOT NULL , ca_street_number CHARACTER(10) , ca_street_name CHARACTER varying(60) , ca_street_type CHARACTER(15) , ca_suite_number CHARACTER(10) ) DISTRIBUTE BY HASH (ca_address_sk) PARTITION BY RANGE(ca_address_sk) ( PARTITION P1 VALUES LESS THAN(2450815), PARTITION P2 VALUES LESS THAN(2451179), PARTITION P3 VALUES LESS THAN(2451544), PARTITION P4 VALUES LESS THAN(MAXVALUE) );
View the information of the partitioned table.
SELECT relname, boundaries FROM pg_partition p where p.parentid='customer_address'::regclass ORDER BY 1; relname | boundaries ------------------+------------ customer_address | p1 | {2450815} p2 | {2451179} p3 | {2451544} p4 | {NULL} (5 rows)
Query the number of rows in the P1 partition:
SELECT count(*) FROM customer_address PARTITION (P1); SELECT count(*) FROM customer_address PARTITION FOR (2450815);
Example 2: Use the START END syntax to create a column-store range partitioned table.
CREATE TABLE customer_address_SE ( ca_address_sk INTEGER NOT NULL , ca_address_id CHARACTER(16) NOT NULL , ca_street_number CHARACTER(10) , ca_street_name CHARACTER varying(60) , ca_street_type CHARACTER(15) , ca_suite_number CHARACTER(10) ) WITH (ORIENTATION = COLUMN) DISTRIBUTE BY HASH (ca_address_sk) PARTITION BY RANGE(ca_address_sk) ( PARTITION p1 START(1) END(1000) EVERY(200), PARTITION p2 END(2000), PARTITION p3 START(2000) END(5000) );
View the information of the partitioned table.
SELECT relname, boundaries FROM pg_partition p where p.parentid='customer_address_SE'::regclass ORDER BY 1; relname | boundaries ---------------------+------------ customer_address_se | p1_0 | {1} p1_1 | {201} p1_2 | {401} p1_3 | {601} p1_4 | {801} p1_5 | {1000} p2 | {2000} p3 | {5000} (9 rows)
Example 3: Create a list partitioned table with partition keys.
CREATE TABLE data_list ( id int, time int, sarlay decimal(12,2) ) PARTITION BY LIST (time) ( PARTITION P1 VALUES (202209), PARTITION P2 VALUES (202210,202208), PARTITION P3 VALUES (202211), PARTITION P4 VALUES (202212), PARTITION P5 VALUES (202301) );
Example 4: Create list partitioned tables with partition keys.
A partitioned table has two partition keys: period and city.
CREATE TABLE sales_info ( sale_time timestamptz, period int, city text, price numeric(10,2), remark varchar2(100) ) DISTRIBUTE BY HASH(sale_time) PARTITION BY LIST (period, city) ( PARTITION north_2022 VALUES (('202201', 'north1'), ('202202', 'north2')), PARTITION south_2022 VALUES (('202201', 'south1'), ('202202', 'south2'), ('202203', 'south2')), PARTITION rest VALUES (DEFAULT) );
Example 5: Create a partitioned table with automatic partition management but without specified partitions. Set PERIOD to 1 day and the partition key to time.
CREATE TABLE time_part ( id integer, time timestamp ) with (PERIOD='1 day') partition by range(time);
Two default partitions are created during table creation. The boundary time of the first default partition is the start of the day later than the current time, that is, 2022-12-13 00:00:00. The boundary time of the second default partition is the boundary time of the first partition plus PERIOD, that is, 2022-12-13 00:00:00+1 day=2022-12-14 00:00:00.
SELECT now(); now ------------------------------- 2022-12-12 20:41:21.603172+08 (1 row) SELECT relname, boundaries FROM pg_partition p where p.parentid='time_part'::regclass ORDER BY 1; relname | boundaries ----------------+------------------------- default_part_1 | {"2022-12-13 00:00:00"} default_part_2 | {"2022-12-14 00:00:00"} time_part | (3 rows)
Example 6: Run the following command to create a partitioned table with automatic partition management and specified partitions:
CREATE TABLE CPU( id integer, idle numeric, IO numeric, scope text, IP text, time timestamp ) with (TTL='7 days',PERIOD='1 day') partition by range(time) ( PARTITION P1 VALUES LESS THAN('2022-01-05 16:32:45'), PARTITION P2 VALUES LESS THAN('2022-01-06 16:56:12') );
Example 7: Create a partitioned table customer_address partitioned by month. The table has 13 partitions and the partition keys are dates.
Create a partitioned table customer_address.
CREATE TABLE customer_address ( ca_address_sk integer NOT NULL, ca_address_date date NOT NULL ) DISTRIBUTE BY HASH (ca_address_sk) PARTITION BY RANGE (ca_address_date) ( PARTITION p202001 VALUES LESS THAN('20200101'), PARTITION p202002 VALUES LESS THAN('20200201'), PARTITION p202003 VALUES LESS THAN('20200301'), PARTITION p202004 VALUES LESS THAN('20200401'), PARTITION p202005 VALUES LESS THAN('20200501'), PARTITION p202006 VALUES LESS THAN('20200601'), PARTITION p202007 VALUES LESS THAN('20200701'), PARTITION p202008 VALUES LESS THAN('20200801'), PARTITION p202009 VALUES LESS THAN('20200901'), PARTITION p202010 VALUES LESS THAN('20201001'), PARTITION p202011 VALUES LESS THAN('20201101'), PARTITION p202012 VALUES LESS THAN('20201201'), PARTITION p202013 VALUES LESS THAN(MAXVALUE) );
Insert data:
INSERT INTO customer_address values('1','20200215'); INSERT INTO customer_address values('7','20200805'); INSERT INTO customer_address values('9','20201111'); INSERT INTO customer_address values('4','20201231');
Query a partition:
SELECT * FROM customer_address PARTITION(p202009); ca_address_sk | ca_address_date ---------------+--------------------- 7 | 2020-08-05 00:00:00 (1 row)
Example 8: Use START END to create a partitioned table with multiple partitions at a time.
Create a partitioned table day_part. Each day is a partition, and the partition key is a date.
CREATE table day_part(id int,d_time date) DISTRIBUTE BY HASH (id) PARTITION BY RANGE (d_time) (PARTITION p1 START('2022-01-01') END('2022-01-31') EVERY(interval '1 day')); ALTER TABLE day_part ADD PARTITION pmax VALUES LESS THAN (maxvalue);
Create a partitioned table week_part, seven days as a partition, and the partition key is a date.
CREATE table week_part(id int,w_time date) DISTRIBUTE BY HASH (id) PARTITION BY RANGE (w_time) (PARTITION p1 START('2021-01-01') END('2022-01-01') EVERY(interval '7 day')); ALTER TABLE week_part ADD PARTITION pmax VALUES LESS THAN (maxvalue);
Create the partition table month_part, each month as a partition, and the partition key is a date.
CREATE table month_part(id int,m_time date) DISTRIBUTE BY HASH (id) PARTITION BY RANGE (m_time) (PARTITION p1 START('2021-01-01') END('2022-01-01') EVERY(interval '1 month')); ALTER TABLE month_part ADD PARTITION pmax VALUES LESS THAN (maxvalue);
Example 9: Create a table for hot and cold data.
Only a column-store partitioned table is supported. Use the default OBS tablespace. Set LMT to 30 for cold and hot switchover rules.
CREATE TABLE cold_hot_table ( W_WAREHOUSE_ID CHAR(16) NOT NULL, W_WAREHOUSE_NAME VARCHAR(20) , W_STREET_NUMBER CHAR(10) , W_STREET_NAME VARCHAR(60) , W_STREET_ID CHAR(15) , W_SUITE_NUMBER CHAR(10) ) WITH (ORIENTATION = COLUMN, storage_policy = 'LMT:30') DISTRIBUTE BY HASH (W_WAREHOUSE_ID) PARTITION BY RANGE(W_STREET_ID) ( PARTITION P1 VALUES LESS THAN(100000), PARTITION P2 VALUES LESS THAN(200000), PARTITION P3 VALUES LESS THAN(300000), PARTITION P4 VALUES LESS THAN(MAXVALUE) )ENABLE ROW MOVEMENT;