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10 changes: 0 additions & 10 deletions _includes/v19.2/known-limitations/cte-by-name.md
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113 changes: 46 additions & 67 deletions _includes/v19.2/sql/diagrams/with_clause.html
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111 changes: 66 additions & 45 deletions v19.2/common-table-expressions.md
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Expand Up @@ -31,6 +31,12 @@ Parameter | Description

## Overview

{{site.data.alerts.callout_info}}
The examples on this page use MovR, a fictional vehicle-sharing application, to demonstrate CockroachDB SQL statements. To follow along, run [`cockroach demo`](cockroach-demo.html) 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](movr.html).
{{site.data.alerts.end}}

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`.
Expand All @@ -39,24 +45,32 @@ For example:

{% include copy-clipboard.html %}
~~~ sql
> WITH o AS (SELECT * FROM orders WHERE id IN (33, 542, 112))
SELECT *
FROM customers AS c, o
WHERE o.customer_id = c.id;
> WITH r AS (SELECT * FROM rides WHERE revenue > 98)
SELECT * FROM users AS u, r WHERE r.rider_id = u.id;
~~~

In this example, the `WITH` clause defines the temporary name `o` for
the subquery over `orders`, and that name becomes a valid table name
~~~
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](table-expressions.html) of the
subsequent `SELECT` clause.

This query is equivalent to, but arguably simpler to read than:

{% include copy-clipboard.html %}
~~~ sql
> SELECT *
FROM customers AS c, (SELECT * FROM orders WHERE id IN (33, 542, 112)) AS o
WHERE o.customer_id = c.id;
> 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
Expand All @@ -66,12 +80,12 @@ following query is equivalent to the two examples above:

{% include copy-clipboard.html %}
~~~ sql
> WITH o AS (SELECT * FROM orders WHERE id IN (33, 542, 112)),
results AS (SELECT * FROM customers AS c, o WHERE o.customer_id = c.id)
> 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 `o`
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
Expand All @@ -80,9 +94,10 @@ It is possible to use a `WITH` clause in a subquery, or even a `WITH` clause wit

{% include copy-clipboard.html %}
~~~ sql
> WITH a AS (SELECT * FROM (WITH b AS (SELECT * FROM c)
SELECT * FROM b))
SELECT * FROM a;
> WITH u AS
(SELECT * FROM
(WITH u_tab AS (SELECT * FROM users) SELECT * FROM u_tab))
SELECT * FROM u;
~~~

When analyzing [table expressions](table-expressions.html) that
Expand All @@ -91,41 +106,38 @@ closest to the table expression. For example:

{% include copy-clipboard.html %}
~~~ sql
> WITH a AS (TABLE x),
b AS (WITH a AS (TABLE y)
SELECT * FROM a)
SELECT * FROM b;
> 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 a` will select from
table `y` (closest `WITH` clause), not from table `x`.
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`,
It is possible to use a [data-modifying statement](sql-statements.html#data-manipulation-statements) (`INSERT`, `DELETE`,
etc.) as a common table expression.

For example:

{% include copy-clipboard.html %}
~~~ sql
> WITH v AS (INSERT INTO t(x) VALUES (1), (2), (3) RETURNING x)
SELECT x+1 FROM v
> 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;
~~~

However, the following restriction applies: only `WITH` sub-clauses at
the top level of a SQL statement can contain data-modifying
statements. The example above is valid, but the following is not:

{% include copy-clipboard.html %}
~~~ sql
> SELECT x+1 FROM
(WITH v AS (INSERT INTO t(x) VALUES (1), (2), (3) RETURNING x)
SELECT * FROM v);
~~~

This is not valid because the `WITH` clause that defines an `INSERT`
common table expression is not at the top level of the query.
rules
+-----------------------------------------------+
{"type": "percent_discount", "value": "50%"}
{"type": "percent_discount", "value": "100%"}
(2 rows)
~~~

{{site.data.alerts.callout_info}}
If a common table expression contains
Expand All @@ -137,20 +149,29 @@ href="subqueries.html#data-writes-in-subqueries">Data
Writes in Subqueries</a> for details.
{{site.data.alerts.end}}

<div markdown="1"></div>
## Reusing common table expressions

## Known limitations
<span class="version-tag">New in v19.2:</span> You can reference a CTE multiple times in a single query, using a `WITH` operator.

{{site.data.alerts.callout_info}}
The following limitations may be lifted
in a future version of CockroachDB.
{{site.data.alerts.end}}
For example:

<div markdown="1"></div>
{% include copy-clipboard.html %}
~~~ sql
> 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;
~~~

### Referring to a CTE by name more than once
~~~
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)
~~~

{% include {{ page.version.version }}/known-limitations/cte-by-name.md %}
In this single query, you define two CTE's and then reuse them in a table join.

## See also

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