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Updated on 2023-03-08 GMT+08:00
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How Do I Query the Information About GaussDB(DWS) Column-Store Tables?

The following SQL statements are used to query common information about column-store tables:

Create a column-store partitioned table my_table.

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CREATE TABLE my_table
(
    product_id INT,
    product_name VARCHAR2(40),
    product_quantity INT
 )
WITH (ORIENTATION = COLUMN)
PARTITION BY range(product_quantity)
(
partition my_table_p1 values less than(600),
partition my_table_p2 values less than(800),
partition my_table_p3 values less than(950),
partition my_table_p4 values less than(1000));
 
INSERT INTO my_table VALUES(1011, 'tents', 720);
INSERT INTO my_table VALUES(1012, 'hammock', 890);
INSERT INTO my_table VALUES(1013, 'compass', 210);
INSERT INTO my_table VALUES(1014, 'telescope', 490);
INSERT INTO my_table VALUES(1015, 'flashlight', 990);
INSERT INTO my_table VALUES(1016, 'ropes', 890);

Run the following command to view the created column-store partitioned table:

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SELECT * FROM my_table;
 product_id | product_name | product_quantity
------------+--------------+------------------
       1013 | compass      |              210
       1014 | telescope    |              490
       1011 | tents        |              720
       1015 | flashlight   |              990
       1012 | hammock      |              890
       1016 | ropes        |              890
(6 rows)

Querying the Boundary of a Partition

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SELECT relname, partstrategy, boundaries FROM pg_partition where parentid=(select parentid from pg_partition where relname='my_table');
   relname   | partstrategy | boundaries
-------------+--------------+------------
 my_table    | r            |
 my_table_p1 | r            | {600}
 my_table_p2 | r            | {800}
 my_table_p3 | r            | {950}
 my_table_p4 | r            | {1000}
(5 rows)

Querying the Number of Columns in a Column-Store Table

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SELECT count(*) FROM ALL_TAB_COLUMNS where table_name='my_table';
 count
-------
     3
(1 row)

Querying Data Distribution on DNs

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SELECT table_skewness('my_table');
           table_skewness
------------------------------------
 ("dn_6007_6008        ",3,50.000%)
 ("dn_6009_6010        ",2,33.333%)
 ("dn_6003_6004        ",1,16.667%)
 ("dn_6001_6002        ",0,0.000%)
 ("dn_6005_6006        ",0,0.000%)
 ("dn_6011_6012        ",0,0.000%)
(6 rows)

Querying the Names of the Cudesc and Delta Tables in Partition P1 on a DN

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EXECUTE DIRECT ON (dn_6003_6004) 'select a.relname from pg_class a, pg_partition b where (a.oid=b.reldeltarelid or a.oid=b.relcudescrelid) and b.relname=''my_table_p1''';
       relname
----------------------
 pg_delta_part_60317
 pg_cudesc_part_60317
(2 rows)
Parent topic: Database Usage