add porting postgres page #1328

maddyblue · 2017-04-24T20:04:14Z

Fixes #1327

This change is

Fixes #1327

cockroach-teamcity · 2017-04-24T20:05:55Z

http://cockroach-docs-review.s3-website-us-east-1.amazonaws.com/513b951b0d3df949c88d1e97e3acd2dc02b19e8c/

jseldess

LGTM, with some minor nits. Thanks very much, @mjibson!

jseldess · 2017-04-24T21:17:14Z

_data/sidebar_doc.yml


        - title: Information Schema
          url: /information-schema.html
+          thirdlevel:


For consistency with the rest of the file, would you mind formatting this as follows?

thirdlevel: - title: Porting Applications thirdlevelitems: - title: From PostgreSQL url: /porting-postgres.html

jseldess · 2017-04-24T21:17:53Z

_data/sidebar_doc.yml

+          - title: Porting Applications
+            thirdlevelitems:
+
+              - title: Postgres


I think it'd be clearer to use the title From PostgreSQL here.

jseldess · 2017-04-24T21:20:31Z

porting-postgres.md

+toc: false
+---
+
+Although CockroachDB supports Postgres syntax and drivers, it does not offer exact compatibility. This page documents the known list of differences between Postgres and CockroachDB for identical input. That is, a SQL statement of the type listed here will behave differently than in Postgres. Porting an existing application to CockroachDB will require changing these expressions.


Let's use PostgreSQL throughout instead of Postgres.

jseldess · 2017-04-24T21:24:02Z

porting-postgres.md

+ERROR:  zero raised to a negative power is undefined
+```
+
+In CockroachDB these expressions will instead return Infinity:


Add comma after In CockroachDB

jseldess · 2017-04-24T21:26:33Z

porting-postgres.md

+In CockroachDB these expressions will instead return Infinity:
+
+```
+root@:26257/> select 1e300::float * 1e10::float;


For the sql prompt, let's use >. Also, can you capitalize the keywords and break commands and responses into separate code blocks, where the commands have sql syntax highlighting and the responses have node?

jseldess · 2017-04-24T21:35:03Z

porting-postgres.md

+
+### Integer division
+
+Division of integers in Postgres results in an integer. The query:


Again, I'd rewrite this so the code block doesn't interrupt the sentence:

For example, the following query returns 1, since the 1 / 2 is truncated to 0 since it is performing integer division:

SELECT 1 + 1 / 2

CockroachDB instead provides the // operator to perform floor division.

jseldess · 2017-04-24T21:35:32Z

porting-postgres.md

+
+In CockroachDB, unary `~` has the same (high) precedence as unary `-`, so the above expression will be parsed as `(~1) + 2`.
+
+**Porting instructions:** manually add parentheses around expressions that depend on the Postgres behavior.


Capitalize Manually

jseldess · 2017-04-24T21:35:59Z

porting-postgres.md

+
+Returns `1`, since the `1 / 2` is truncated to `0` since it is performing integer division. In CockroachDB integer division results in a `decimal`. CockroachDB instead provides the `//` operator to perform floor division.
+
+**Porting instructions:** change `/` to `//` in integer division where the result must be an integer.


Capitalize Change

jseldess · 2017-04-24T21:37:26Z

porting-postgres.md

+
+### Shift argument modulo
+
+The shift operators in Postgres (`<<`, `>>`) sometimes modulo their second argument to the bit size of the underlying type. For example:


Again, revise so the sample doesn't interrupt the sentence:

For example, the following query results in a 1 because the int type is 32 bits, and 32 % 32 is 0, so this is the equivalent of 1 << 0:

SELECT 1::int << 32

In CockroachDB, no such modulo is performed.

jseldess · 2017-04-24T21:40:07Z

porting-postgres.md

+
+Results in a `1` because the `int` type is 32 bits, and `32 % 32` is `0`, so this is the equivalent of `1 << 0`. In CockroachDB, no such modulo is performed.
+
+**Porting instructions:** manually add a modulo to the second argument. Also note that CockroachDB's int type is always 64 bits. For example:


Capitalize Manually. Also, let's capitalize INT and link to our docs:

[`INT`](int.html)

cockroach-teamcity · 2017-04-25T04:26:21Z

http://cockroach-docs-review.s3-website-us-east-1.amazonaws.com/1e22119a3c909ac059d20854b55e77495f2e8a4f/

cockroach-teamcity · 2017-04-25T04:33:48Z

http://cockroach-docs-review.s3-website-us-east-1.amazonaws.com/a420b84997412001498d203c2d394f57568b807d/

jseldess

LGTM, with a few final comments

jseldess · 2017-04-25T14:22:06Z

porting-postgres.md

+SELECT ~1 + 2
+```
+
+Is parsed as `~ (1 + 2)` because `~` has a lower precedence than `+`.


We don't need this line anymore.

jseldess · 2017-04-25T15:49:29Z

porting-postgres.md

+
+### Integer division
+
+Division of integers in PostgreSQL results in an integer. For example, the following query returns `1`, since the `1 / 2` is truncated to `0` since it is performing integer division:


I'd actually remove since it is performing integer division. Feels redundant and makes the sentence a bit convoluted.

sploiselle · 2017-04-25T16:32:16Z

I'd recommend mentioning that this guide primarily focuses on expressions and does not demonstrate how to port applications that use unsupported SQL features (e.g. arrays, enum).

jseldess · 2017-04-25T16:33:57Z

Good point, @sploiselle. We may want to expand this page to cover a lot more, but for now, totally agree that it's best to be clear about the focus.

sploiselle · 2017-04-25T16:37:21Z

Review status: 0 of 2 files reviewed at latest revision, 15 unresolved discussions.

porting-postgres.md, line 9 at r3 (raw file):

Although CockroachDB supports PostgreSQL syntax and drivers, it does not offer exact compatibility. This page documents the known list of differences between PostgreSQL and CockroachDB for identical input. That is, a SQL statement of the type listed here will behave differently than in PostgreSQL. Porting an existing application to CockroachDB will require changing these expressions.

Note that some of these differences only apply to rare inputs, and so no change will be needed, even if the listed feature is being used. In these cases, it is safe to ignore the porting instructions.

After this line, recommend adding something like:

{{site.data.alerts.callout_info}}This document currently only covers how to rewrite SQL expressions. It does not discuss strategies for porting application that use SQL features CockroachDB does not currently support, such as arrays or the ENUM type.{{site.data.alerts.end}}

Comments from Reviewable

maddyblue · 2017-04-25T20:23:27Z

I've made those changes. RFAL.

cockroach-teamcity · 2017-04-25T20:25:09Z

http://cockroach-docs-review.s3-website-us-east-1.amazonaws.com/41f055a4b27159a0ff7927d60fcf506868207e8e/

jseldess

LGTM, with one final nit.

jseldess · 2017-04-25T20:25:49Z

porting-postgres.md


 Note that some of these differences only apply to rare inputs, and so no change will be needed, even if the listed feature is being used. In these cases, it is safe to ignore the porting instructions.

+{{site.data.alerts.callout_info}}This document currently only covers how to rewrite SQL expressions. It does not discuss strategies for porting application that use [SQL features CockroachDB does not currently support](/sql-feature-support.html), such as arrays or the `ENUM` type.{{site.data.alerts.end}}


porting applications - needs to be plural

cockroach-teamcity · 2017-04-26T03:35:40Z

http://cockroach-docs-review.s3-website-us-east-1.amazonaws.com/9f85980e2dd4b3edb96e19fc160d3ee7137b98b3/

cockroach-teamcity · 2017-04-26T04:02:45Z

http://cockroach-docs-review.s3-website-us-east-1.amazonaws.com/bc913340bd06f8ad42b69fac4751e6d842ee3188/

cockroach-teamcity · 2017-04-26T04:08:11Z

http://cockroach-docs-review.s3-website-us-east-1.amazonaws.com/9ce50cc21688efebe5ace00ba6b87f3a28624dc2/

…ckroachdb#1328) * Optimize access of last element in traversals * Remove no longer existing patch-update-statements AQL optimizer rule * Account for optimizer rules that are applied a 3rd time (-3) suffix --------- Co-authored-by: Paula Mihu <97217318+nerpaula@users.noreply.github.com>

add porting postgres page

513b951

Fixes #1327

maddyblue requested a review from jseldess April 24, 2017 20:04

jseldess approved these changes Apr 24, 2017

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jseldess approved these changes Apr 25, 2017

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maddyblue merged commit 249e0fa into gh-pages Apr 26, 2017

maddyblue deleted the porting-postgres branch April 26, 2017 05:33

jseldess mentioned this pull request Apr 26, 2017

Minor formatting fixes in Porting from PostgreSQL #1332

Merged


		### Integer division

		Division of integers in Postgres results in an integer. The query:


		In CockroachDB, unary `~` has the same (high) precedence as unary `-`, so the above expression will be parsed as `(~1) + 2`.

		Porting instructions: manually add parentheses around expressions that depend on the Postgres behavior.


		Returns `1`, since the `1 / 2` is truncated to `0` since it is performing integer division. In CockroachDB integer division results in a `decimal`. CockroachDB instead provides the `//` operator to perform floor division.

		Porting instructions: change `/` to `//` in integer division where the result must be an integer.


		### Shift argument modulo

		The shift operators in Postgres (`<<`, `>>`) sometimes modulo their second argument to the bit size of the underlying type. For example:


		Results in a `1` because the `int` type is 32 bits, and `32 % 32` is `0`, so this is the equivalent of `1 << 0`. In CockroachDB, no such modulo is performed.

		Porting instructions: manually add a modulo to the second argument. Also note that CockroachDB's int type is always 64 bits. For example:


		### Integer division

		Division of integers in PostgreSQL results in an integer. For example, the following query returns `1`, since the `1 / 2` is truncated to `0` since it is performing integer division:


		Note that some of these differences only apply to rare inputs, and so no change will be needed, even if the listed feature is being used. In these cases, it is safe to ignore the porting instructions.

		{{site.data.alerts.callout_info}}This document currently only covers how to rewrite SQL expressions. It does not discuss strategies for porting application that use [SQL features CockroachDB does not currently support](/sql-feature-support.html), such as arrays or the `ENUM` type.{{site.data.alerts.end}}

add porting postgres page #1328

add porting postgres page #1328

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cockroach-teamcity commented Apr 25, 2017

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cockroach-teamcity commented Apr 26, 2017

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maddyblue commented Apr 24, 2017 •

edited by andreimatei

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