The queries in the following example set all use the multilevel partitioned table defined by the following CREATE TABLE request.
CREATE TABLE markets (
productid INTEGER NOT NULL,
region BYTEINT NOT NULL,
activity_date DATE FORMAT 'yyyy-mm-dd' NOT NULL,
revenue_code BYTEINT NOT NULL,
business_sector BYTEINT NOT NULL,
note VARCHAR(256))
PRIMARY INDEX (productid, region)
PARTITION BY (
RANGE_N(region BETWEEN 1
AND 9
EACH 3),
RANGE_N(business_sector BETWEEN 0
AND 49
EACH 10),
RANGE_N(revenue_code BETWEEN 1
AND 34
EACH 2),
RANGE_N(activity_date BETWEEN DATE '1986-01-01'
AND DATE '2007-05-31'
EACH INTERVAL '1' MONTH));
Note the following details about the partitioning of this table.
|
Number of Row Partitioning Level |
Partitioning Column for This Level |
Number of Row Partitions Defined at This Level |
|
1 |
region |
3 |
|
2 |
business_sector |
5 |
|
3 |
revenue_code |
17 |
|
4 |
activity_date |
257 |
where:
|
Equation element … |
Specifies … |
|
PLn |
the number of partitions at level n. |
For the sake of simplicity, the comments associated with the example queries make the following assumptions.
If the example queries were not able to capitalize on static row partition elimination, they would all require all‑AMP, full‑table scans to be processed.
For the following query, Teradata Database reads only row partition 2 at level 1 on
all AMPs. As a result, it reads roughly 
(33.3%) of the data blocks for the markets table because there are 3 row partitions at level 1, and Teradata Database needs
to read only one of them to access all of the qualified rows.
Row partition 2 includes rows with a value of 5 or 6 for region. Teradata Database necessarily reads those rows as it reads row partition 2, but they do not qualify for the query predicate, so they are not returned in the results set.
SELECT *
FROM markets
WHERE region=4;
For the following query, Teradata Database reads only partitions 4 and 5 at level
2 on all AMPs. As a result, it reads roughly 
(40%) of the data blocks for the markets table because there are 5 row partitions at level 2, and Teradata Database needs
to read 2 of those 5 to access all of the qualified rows.
Row partition 4 includes rows whose value for business_sector is 30. Teradata Database necessarily reads those rows as it reads partition 4, but they do not qualify for the query predicate, so they are not returned in the results set.
SELECT *
FROM markets
WHERE business_sector>30;
For the following query, Teradata Database reads only partitions 1, 2, and 3 at level
3 on all AMPs. As a result, it reads roughly 
(17.6%) of the data blocks for the markets table because there are 17 row partitions at level 3, and the system needs to read
only 3 of them to access all of the qualified rows.
Partition 3 includes rows who value for revenue_code is 6. Teradata Database necessarily reads those rows as it reads partition 5, but they do not qualify for the query predicate, so they are not returned in the results set.
SELECT *
FROM markets
WHERE revenue_code<5;
For the following query, Teradata Database reads only partitions 50 and 51 at level
4 on all AMPs. As a result, it reads roughly 
(0.78%) of the data blocks for the markets table because there are 257 row partitions at level 4, and the system needs to read
only 2 of them to access all of the qualified rows.
Both partition 50 and partition 51 include rows that do not meet the predicate for the query. Teradata Database necessarily reads those rows as it reads the row partitions, but they do not qualify for the query predicate, so they are not returned in the results set.
SELECT *
FROM markets
WHERE activity_date>=DATE '1990-02-12'
AND activity_date<=DATE '1990-03-28';
For the following query, the system reads partitions 4 and 5 at level 2 on all AMPs
and partition 2 at level 1 on all AMPs. As a result, it reads roughly 
(13.3%) of the data blocks for the markets table because there are 15 partitions at combined levels 1 and 2 (the combined total
is 3 x 5 = 15), 3 at level 1 and 5 at level 2, and the system needs to read only 2
of them to access all of the qualified rows.
Note that all of these partitions contain some rows that do not qualify for the query predicate, so the system does not return them in the results set.
SELECT *
FROM markets
WHERE region=4
AND business_sector>30;
For the following query, Teradata Database reads the following set of row partitions at the indicated levels on all AMPs: 2 row partitions of level 4 (partitions 50 and 51), in 3 row partitions at level 3 (partitions 1, 2, and 3), and in 2 row partitions at level 2 (partitions 4 and 5).
|
Level Number |
Number of Row Partitions Read at This Level |
Partition Numbers Read Within the Level |
|
2 |
2 |
|
|
3 |
3 |
|
|
4 |
2 |
|
As a result, Teradata Database reads roughly 
(0.05%) of the data blocks for the markets table because there are 21,845 partitions (the combined total is 5 x 17 x 257 = 21,845)
at combined levels 2, 3, and 4, and the system needs to read only 12 of them (the
combined total is 2 x 3 x 2 = 12) to access all of the qualified rows.
All of these partitions contain some rows that do not qualify for the query predicate, so Teradata Database does not return them in the results set.
SELECT *
FROM markets
WHERE business_sector>30
AND revenue_code<5
AND activity_date>=DATE '1990-02-12'
AND activity_date<=DATE '1990-03-28';
For the following query, Teradata Database reads the following set of row partitions at the indicated levels on all AMPs: 2 row partitions of level 4 (partitions 50 and 51), in 3 row partitions at level 3 (partitions 1, 2, and 3), in 2 row partitions at level 2 (partitions 4 and 5), in 1 row partition of level 1 (partition 2).
|
Level Number |
Number of Partitions Read at This Level |
Partition Numbers Read Within the Level |
|
1 |
1 |
2 |
|
2 |
2 |
|
|
3 |
3 |
|
|
4 |
2 |
|
As a result, Teradata Database reads roughly 
(0.18%) of the data blocks for the markets table because there are 65,535 partitions (the combined total is 3 x 5 x 17 x 257
= 65,535) at combined levels 2, 3, and 4, and Teradata Database needs to read only
12 of them (the combined total is 1 x 2 x 3 x 2 = 12) to access all of the qualified
rows.
All of these partitions contain some rows that do not qualify for the query predicate, so Teradata Database does not return them in the results set.
SELECT *
FROM markets
WHERE region=4
AND business_sector>30
AND revenue_code<5
AND activity_date>=DATE '1990-02-12'
AND activity_date<=DATE '1990-03-28';
For the following query, Teradata Database reads one row partition at level 2 on all
AMPs: partition 1. As a result, it reads roughly 
(20.0%) of the data blocks for the markets table because there are 5 row partitions at level 2, and Teradata Database needs
to read only one of them to access all of the qualified rows.
The row partition Teradata Database must read contains the rows having a value for business_sector between 0 and 9, inclusive.
This row partition contains some rows that do not qualify for the query predicate, so the system does not return them in the results set.
SELECT *
FROM markets
WHERE PARTITION#L2=1;
For the following query, Teradata Database reads one combined row partition on all
AMPs because the specified predicate is an equality condition on the combined partition
that is equal to 32,531. As a result, it reads only 
(0.15%) of the data blocks for the markets table because there is only one combined partition that has the value 32,531, and
the system needs to read only the data block that contains combined partition number
32,531 to access all of the qualified rows.
The row partition Teradata Database must read contains the rows defined by the following value set.
|
PARTITION#Ln |
PARTITION Value Where Qualified Rows Are Stored |
Conditions Mapped To This PARTITION Value Range |
|
1 |
2 |
region BETWEEN 4 AND 6 |
|
2 |
3 |
business_sector BETWEEN 20 AND 29 |
|
3 |
8 |
revenue_code BETWEEN 15 AND 16 |
|
4 |
149 |
activity_date BETWEEN 1998-05-01 AND 1998-05-31 |
SELECT *
FROM markets
WHERE PARTITION=32531;