Common Table Expressions, or CTEs, provide a shorthand name to a possibly complex subquery before it is used in a larger query context. This improves readability of the SQL code.
CTEs can be used in combination with SELECT
clauses and INSERT,
DELETE, UPDATE and
UPSERT statements.
Synopsis
Parameters
| Parameter | Description |
|---|---|
table_alias_name |
The name to use to refer to the common table expression from the accompanying query or statement. |
name |
A name for one of the columns in the newly defined common table expression. |
preparable_stmt |
The statement or subquery to use as common table expression. |
Overview
The examples on this page use MovR, a fictional vehicle-sharing application, to demonstrate CockroachDB SQL statements. To follow along, run cockroach demo from the command line to start a temporary, in-memory cluster with the movr dataset preloaded.
For more information about the MovR example application and dataset, see MovR: A Global Vehicle-sharing App.
A query or statement of the form WITH x AS y IN z creates the
temporary table name x for the results of the subquery y, to be
reused in the context of the query z.
For example:
> WITH r AS (SELECT * FROM rides WHERE revenue > 98)
SELECT * FROM users AS u, r WHERE r.rider_id = u.id;
id | city | name | address | credit_card | id | city | vehicle_city | rider_id | vehicle_id | start_address | end_address | start_time | end_time | revenue
+--------------------------------------+---------------+------------------+--------------------------------+-------------+--------------------------------------+---------------+---------------+--------------------------------------+--------------------------------------+-----------------------------------+---------------------------+---------------------------+---------------------------+---------+
ae147ae1-47ae-4800-8000-000000000022 | amsterdam | Tyler Dalton | 88194 Angela Gardens Suite 94 | 4443538758 | bbe76c8b-4395-4000-8000-00000000016f | amsterdam | amsterdam | ae147ae1-47ae-4800-8000-000000000022 | aaaaaaaa-aaaa-4800-8000-00000000000a | 45295 Brewer View Suite 52 | 62188 Jade Causeway | 2018-12-17 03:04:05+00:00 | 2018-12-17 13:04:05+00:00 | 99.00
c7ae147a-e147-4000-8000-000000000027 | paris | Tina Miller | 97521 Mark Extensions | 8880478663 | d5810624-dd2f-4800-8000-0000000001a1 | paris | paris | c7ae147a-e147-4000-8000-000000000027 | cccccccc-cccc-4000-8000-00000000000c | 47713 Reynolds Mountains Suite 39 | 1417 Stephanie Villages | 2018-12-17 03:04:05+00:00 | 2018-12-18 22:04:05+00:00 | 99.00
75c28f5c-28f5-4400-8000-000000000017 | san francisco | William Wood | 36021 Steven Cove Apt. 89 | 5669281259 | 8ac08312-6e97-4000-8000-00000000010f | san francisco | san francisco | 75c28f5c-28f5-4400-8000-000000000017 | 77777777-7777-4800-8000-000000000007 | 84407 Tony Crest | 55336 Jon Manors | 2018-12-10 03:04:05+00:00 | 2018-12-11 13:04:05+00:00 | 99.00
8a3d70a3-d70a-4000-8000-00000000001b | san francisco | Jessica Martinez | 96676 Jennifer Knolls Suite 91 | 1601930189 | 7d70a3d7-0a3d-4000-8000-0000000000f5 | san francisco | san francisco | 8a3d70a3-d70a-4000-8000-00000000001b | 77777777-7777-4800-8000-000000000007 | 78978 Stevens Ramp Suite 8 | 7340 Alison Field Apt. 44 | 2018-12-19 03:04:05+00:00 | 2018-12-21 10:04:05+00:00 | 99.00
47ae147a-e147-4000-8000-00000000000e | washington dc | Patricia Herrera | 80588 Perez Camp | 6812041796 | 4083126e-978d-4000-8000-00000000007e | washington dc | washington dc | 47ae147a-e147-4000-8000-00000000000e | 44444444-4444-4400-8000-000000000004 | 33055 Julie Dale Suite 93 | 17280 Jill Drives | 2019-01-01 03:04:05+00:00 | 2019-01-01 14:04:05+00:00 | 99.00
(5 rows)
In this example, the WITH clause defines the temporary name r for
the subquery over rides, and that name becomes a valid table name
for use in any table expression of the
subsequent SELECT clause.
This query is equivalent to, but arguably simpler to read than:
> SELECT * FROM users AS u, (SELECT * FROM rides WHERE revenue > 98) AS r
WHERE r.rider_id = u.id;
It is also possible to define multiple common table expressions
simultaneously with a single WITH clause, separated by commas. Later
subqueries can refer to earlier subqueries by name. For example, the
following query is equivalent to the two examples above:
> WITH r AS (SELECT * FROM rides WHERE revenue > 98),
results AS (SELECT * FROM users AS u, r WHERE r.rider_id = u.id)
SELECT * FROM results;
In this example, the second CTE results refers to the first CTE r
by name. The final query refers to the CTE results.
Nested WITH clauses
It is possible to use a WITH clause in a subquery, or even a WITH clause within another WITH clause. For example:
> WITH u AS
(SELECT * FROM
(WITH u_tab AS (SELECT * FROM users) SELECT * FROM u_tab))
SELECT * FROM u;
When analyzing table expressions that mention a CTE name, CockroachDB will choose the CTE definition that is closest to the table expression. For example:
> WITH
u AS (SELECT * FROM users),
v AS (WITH u AS (SELECT * from vehicles) SELECT * FROM u)
SELECT * FROM v;
In this example, the inner subquery SELECT * FROM v will select from
table vehicles (closest WITH clause), not from table users.
Data modifying statements
It is possible to use a data-modifying statement (INSERT, DELETE,
etc.) as a common table expression.
For example:
> WITH final_code AS
(INSERT INTO promo_codes(code, description, rules)
VALUES ('half_off', 'Half-price ride!', '{"type": "percent_discount", "value": "50%"}'), ('free_ride', 'Free ride!', '{"type": "percent_discount", "value": "100%"}')
returning rules)
SELECT rules FROM final_code;
rules
+-----------------------------------------------+
{"type": "percent_discount", "value": "50%"}
{"type": "percent_discount", "value": "100%"}
(2 rows)
If a common table expression contains
a data-modifying statement (INSERT, DELETE,
etc.), the modifications are performed fully even if only part
of the results are used, e.g., with LIMIT. See Data
Writes in Subqueries for details.
Reusing common table expressions
New in v19.2: You can reference a CTE multiple times in a single query, using a WITH operator.
For example:
> WITH
users_ny AS (SELECT name, id FROM users WHERE city='new york'),
vehicles_ny AS (SELECT type, id, owner_id FROM vehicles WHERE city='new york')
SELECT * FROM users_ny JOIN vehicles_ny ON users_ny.id = vehicles_ny.owner_id;
name | id | type | id | owner_id
+------------------+--------------------------------------+------------+--------------------------------------+--------------------------------------+
James Hamilton | 051eb851-eb85-4ec0-8000-000000000001 | skateboard | 00000000-0000-4000-8000-000000000000 | 051eb851-eb85-4ec0-8000-000000000001
Catherine Nelson | 147ae147-ae14-4b00-8000-000000000004 | scooter | 11111111-1111-4100-8000-000000000001 | 147ae147-ae14-4b00-8000-000000000004
(2 rows)
In this single query, you define two CTE's and then reuse them in a table join.
See also
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