DB2 Version 9.7 for Linux, UNIX, and Windows

Defining ranges on partitioned tables

You can specify a range for each data partition when you create a partitioned table. A partitioned table uses a data organization scheme in which table data is divided across multiple data partitions according to the values of the table partitioning key columns of the table.

About this task

Data from a given table is partitioned into multiple storage objects based on the specifications provided in the PARTITION BY clause of the CREATE TABLE statement. A range is specified by the STARTING FROM and ENDING AT values of the PARTITION BY clause.

To completely define the range for each data partition, you must specify sufficient boundaries. The following is a list of guidelines to consider when defining ranges on a partitioned table:

The STARTING clause specifies a low boundary for the data partition range. This clause is mandatory for the lowest data partition range (although you can define the boundary as MINVALUE). The lowest data partition range is the data partition with the lowest specified bound.
The ENDING (or VALUES) clause specifies a high boundary for the data partition range. This clause is mandatory for the highest data partition range (although you can define the boundary as MAXVALUE). The highest data partition range is the data partition with the highest specified bound.
If you do not specify an ENDING clause for a data partition, then the next greater data partition must specify a STARTING clause. Likewise, if you do not specify a STARTING clause, then the previous data partition must specify an ENDING clause.
MINVALUE specifies a value that is smaller than any possible value for the column type being used. MINVALUE and INCLUSIVE or EXCLUSIVE cannot be specified together.
MAXVALUE specifies a value that is larger than any possible value for the column type being used. MAXVALUE and INCLUSIVE or EXCLUSIVE cannot be specified together.
INCLUSIVE indicates that all values equal to the specified value are to be included in the data partition containing this boundary.
EXCLUSIVE indicates that all values equal to the specified value are NOT to be included in the data partition containing this boundary.
The NULLS FIRST and NULLS LAST clauses of the CREATE TABLE statement specify whether null values are to be sorted high or low when considering data partition placement. By default, null values are sorted high. Null values in the table partitioning key columns are treated as positive infinity, and are placed in a range ending at MAXVALUE. If no such data partition is defined, null values are considered to be out-of-range values. Use the NOT NULL constraint if you want to exclude null values from table partitioning key columns. LAST specifies that null values are to appear last in a sorted list of values. FIRST specifies that null values are to appear first in a sorted list of values.
When using the long form of the syntax, each data partition must have at least one bound specified.

Tip: Before you begin defining data partitions on a table it is important to understand how tables benefit from table partitioning and what factors influence the columns you choose as partitioning columns.

The ranges specified for each data partition can be generated automatically or manually.

Automatically generated

Automatic generation is a simple method of creating many data partitions quickly and easily. This method is appropriate for equal sized ranges based on dates or numbers.

Examples 1 and 2 demonstrate how to use the CREATE TABLE statement to define and generate automatically the ranges specified for each data partition.

Example 1:

Issue a create table statement with the following ranges defined:

CREATE TABLE lineitem (
  l_orderkey    DECIMAL(10,0) NOT NULL,
  l_quantity    DECIMAL(12,2),
  l_shipdate    DATE,
  l_year_month  INT GENERATED ALWAYS AS (YEAR(l_shipdate)*100 + MONTH(l_shipdate)))
     PARTITION BY RANGE(l_shipdate)
    (STARTING ('1/1/1992') ENDING ('12/31/1992') EVERY 1 MONTH);

This statement results in 12 data partitions each with 1 key value (l_shipdate) >= ('1/1/1992'), (l_shipdate) < ('3/1/1992'), (l_shipdate) < ('4/1/1992'), (l_shipdate) < ('5/1/1992'), ..., (l_shipdate) < ('12/1/1992'), (l_shipdate) < ('12/31/1992').

The starting value of the first data partition is inclusive because the overall starting bound ('1/1/1992') is inclusive (default). Similarly, the ending bound of the last data partition is inclusive because the overall ending bound ('12/31/1992') is inclusive (default). The remaining STARTING values are inclusive and the remaining ENDING values are all exclusive. Each data partition holds n key values where n is given by the EVERY clause. Use the formula (start + every) to find the end of the range for each data partition. The last data partition might have fewer key values if the EVERY value does not divide evenly into the START and END range.

Example 2:

Issue a create table statement with the following ranges defined:

CREATE TABLE t(a INT, b INT) 
	PARTITION BY RANGE(b) (STARTING FROM (1)
  EXCLUSIVE ENDING AT (1000) EVERY (100))

This statement results in 10 data partitions each with 100 key values (1 < b <= 101, 101 < b <= 201, ..., 901 < b <= 1000).

The starting value of the first data partition (b > 1 and b <= 101) is exclusive because the overall starting bound (1) is exclusive. Similarly the ending bound of the last data partition ( b > 901 b <= 1000) is inclusive because the overall ending bound (1000) is inclusive. The remaining STARTING values are all exclusive and the remaining ENDING values are all inclusive. Each data partition holds n key values where n is given by the EVERY clause. Finally, if both the starting and ending bound of the overall clause are exclusive, the starting value of the first data partition is exclusive because the overall starting bound (1) is exclusive. Similarly the ending bound of the last data partition is exclusive because the overall ending bound (1000) is exclusive. The remaining STARTING values are all exclusive and the ENDING values are all inclusive. Each data partition (except the last) holds n key values where n is given by the EVERY clause.

Manually generated

Manual generation creates a new data partition for each range listed in the PARTITION BY clause. This form of the syntax allows for greater flexibility when defining ranges thereby increasing your data and LOB placement options. Examples 3 and 4 demonstrate how to use the CREATE TABLE statement to define and generate manually the ranges specified for a data partition.

Example 3:

This statement partitions on two date columns both of which are generated. Notice the use of the automatically generated form of the CREATE TABLE syntax and that only one end of each range is specified. The other end is implied from the adjacent data partition and the use of the INCLUSIVE option:

CREATE TABLE sales(invoice_date date, inv_month int NOT NULL 
GENERATED ALWAYS AS (month(invoice_date)), inv_year INT NOT 
NULL GENERATED ALWAYS AS ( year(invoice_date)), 
item_id int NOT NULL,
cust_id int NOT NULL) PARTITION BY RANGE (inv_year, 
inv_month)
(PART Q1_02 STARTING (2002,1) ENDING (2002, 3) INCLUSIVE,
PART Q2_02 ENDING (2002, 6) INCLUSIVE,
PART Q3_02 ENDING (2002, 9) INCLUSIVE,
PART Q4_02 ENDING (2002,12) INCLUSIVE,
PART CURRENT ENDING (MAXVALUE, MAXVALUE));

Gaps in the ranges are permitted. The CREATE TABLE syntax supports gaps by allowing you to specify a STARTING value for a range that does not line up against the ENDING value of the previous data partition.

Example 4:

Creates a table with a gap between values 101 and 200.

CREATE TABLE foo(a INT)
	PARTITION BY RANGE(a) 
   (STARTING FROM (1) ENDING AT (100), 
   STARTING FROM (201) ENDING AT (300))

Use of the ALTER TABLE statement, which allows data partitions to be added or removed, can also cause gaps in the ranges.

When you insert a row into a partitioned table, it is automatically placed into the proper data partition based on its key value and the range it falls within. If it falls outside of any ranges defined for the table, the insert fails and the following error is returned to the application:

SQL0327N  The row cannot be inserted into table <tablename>
because it is outside the bounds of the defined data partition ranges. 
   SQLSTATE=22525

Restrictions

Table level restrictions:
- Tables created using the automatically generated form of the syntax (containing the EVERY clause) are constrained to use a numeric or date time type in the table partitioning key.
Statement level restrictions:
- MINVALUE and MAXVALUE are not supported in the automatically generated form of the syntax.
- Ranges are ascending.
- Only one column can be specified in the automatically generated form of the syntax.
- The increment in the EVERY clause must be greater than zero.
- The ENDING value must be greater than or equal to the STARTING value.