Add SQL style guide

.spelling

@@ -24,6 +24,7 @@ blocklist
 boolean
 booleans
 bugzilla
+CamelCase
 CEP
 changesets
 chromehangs
@@ -93,6 +94,7 @@ NumPy
 ORM-like
 parquet2hive
 performant
+Pep8
 Pingsender
 Plotly
 Postgres

SUMMARY.md

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     * [Event Pipeline Detail](/concepts/pipeline/event_pipeline.md)
   * [Analysis Interfaces](tools/interfaces.md)
   * [Custom analysis with Spark](tools/spark.md)
+  * [SQL Style Guide](concepts/sql_style.md)
 * [Cookbooks](cookbooks/README.md)
   * [Alerts](tools/alerts.md)
   * [Working with Parquet Data on ATMO Clusters](cookbooks/parquet.md)

concepts/sql_style.md

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+# SQL Style Guide
+
+## Table of Contents
+
+<!-- toc -->
+
+## Consistency
+
+From [Pep8](https://www.python.org/dev/peps/pep-0008/#a-foolish-consistency-is-the-hobgoblin-of-little-minds):
+
+> A style guide is about consistency.
+> Consistency with this style guide is important.
+> Consistency within a project is more important.
+> Consistency within one module or function is the most important.
+>
+> However, know when to be inconsistent --
+> sometimes style guide recommendations just aren't applicable.
+> When in doubt, use your best judgment.
+> Look at other examples and decide what looks best.
+> And don't hesitate to ask!
+
+## Reserved Words
+
+Always use uppercase for reserved keywords like `SELECT`, `WHERE`, or `AS`.
+
+## Variable Names
+
+1. Use consistent and descriptive identifiers and names.
+1. Use lower case names with underscores, such as `first_name`.
+   Do not use CamelCase.
+1. Presto functions, such as `cardinality`, `approx_distinct`, or `substr`,
+   [are identifiers](https://www.postgresql.org/docs/10/static/sql-syntax-lexical.html#SQL-SYNTAX-IDENTIFIERS)
+   and should be treated like variable names.
+1. Names must begin with a letter and may not end in an underscore.
+1. Only use letters, numbers, and underscores in variable names.
+
+## Aliasing
+
+Always include the `AS` keyword when aliasing a variable,
+it's easier to read when explicit.
+
+**Good**
+```sql
+SELECT
+  SUBSTR(submission_date, 1, 6) AS month
+FROM
+  main_summary
+LIMIT
+  10
+```
+
+**Bad**
+```sql
+SELECT
+  SUBSTR(submission_date, 1, 6) month
+FROM
+  main_summary
+LIMIT
+  10
+```
+
+## Left Align Root Keywords 
+
+Root keywords should all start on the same character boundary.
+This is counter to the common "rivers" pattern
+[described here](https://www.sqlstyle.guide/#spaces).
+
+**Good**:
+
+```sql
+SELECT
+  client_id,
+  submission_date
+FROM
+  main_summary
+WHERE
+  sample_id = '42'
+  AND submission_date > '20180101'
+LIMIT
+  10
+```
+
+**Bad**:
+
+```sql
+SELECT client_id,
+       submission_date
+  FROM main_summary
+ WHERE sample_id = '42'
+   AND submission_date > '20180101'
+```
+
+## Code Blocks
+
+Root keywords should be on their own line.
+For example:
+
+**Good**:
+```sql
+SELECT
+  client_id,
+  submission_date
+FROM
+  main_summary
+WHERE
+  submission_date > '20180101'
+  AND sample_id = '42'
+LIMIT
+  10
+```
+
+It's acceptable to include an argument on the same line as the root keyword,
+if there is exactly one argument.
+
+**Acceptable**:
+```sql
+SELECT
+  client_id,
+  submission_date
+FROM main_summary
+WHERE
+  submission_date > '20180101'
+  AND sample_id = '42'
+LIMIT 10
+```
+
+Do not include multiple arguments on one line.
+
+**Bad**:
+```sql
+SELECT client_id, submission_date
+FROM main_summary
+WHERE
+  submission_date > '20180101'
+  AND sample_id = '42'
+LIMIT 10
+```
+
+**Bad**
+```sql
+SELECT 
+  client_id,
+  submission_date
+FROM main_summary
+WHERE submission_date > '20180101'
+  AND sample_id = '42'
+LIMIT 10
+```
+
+## Parentheses
+
+If parentheses span multiple lines:
+
+1. The opening parenthesis should terminate the line.
+1. The closing parenthesis should be lined up under
+   the first character of the line that starts the multi-line construct.
+1. The contents of the parentheses should be indented one level.
+
+For example:
+
+**Good**
+```sql
+WITH sample AS (
+  SELECT
+    client_id,
+  FROM
+    main_summary
+  WHERE
+    sample_id = '42'
+)
+```
+
+**Bad** (Terminating parenthesis on shared line)
+```sql
+WITH sample AS (
+  SELECT
+    client_id,
+  FROM
+    main_summary
+  WHERE
+    sample_id = '42')
+```
+
+**Bad** (No indent)
+```sql
+WITH sample AS (
+SELECT
+  client_id,
+FROM
+  main_summary
+WHERE
+  sample_id = '42'
+)
+```
+
+## Boolean at the Beginning of Line
+
+`AND` and `OR` should always be at the beginning of the line.
+For example:
+
+**Good**
+```sql
+...
+WHERE
+  submission_date > 20180101
+  AND sample_id = '42'
+```
+
+**Bad**
+```sql
+...
+WHERE
+  submission_date > 20180101 AND
+  sample_id = '42'
+```
+
+## Nested Queries
+
+Do not use nested queries.
+Instead, use common table expressions to improve readability.
+
+**Good**:
+```sql
+WITH sample AS (
+  SELECT
+    client_id,
+    submission_date
+  FROM
+    main_summary
+  WHERE
+    sample_id = '42'
+)
+
+SELECT *
+FROM sample
+LIMIT 10
+```
+
+**Bad**:
+```sql
+SELECT *
+FROM (
+  SELECT
+    client_id,
+    submission_date
+  FROM
+    main_summary
+  WHERE
+    sample_id = '42'
+)
+LIMIT 10
+```
+
+## About this Document
+
+This document was heavily influenced by https://www.sqlstyle.guide/
+
+Changes to the style guide should be reviewed by at least one member of
+both the Data Engineering team and the Data Science team.
+
+