SQL Style Guide

Table of Contents

Consistency

From Pep8:

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.
  2. Use lower case names with underscores, such as first_name. Do not use CamelCase.
  3. Presto functions, such as cardinality, approx_distinct, or substr, are identifiers and should be treated like variable names.
  4. Names must begin with a letter and may not end in an underscore.
  5. 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

SELECT
  substr(submission_date, 1, 6) AS month
FROM
  main_summary
LIMIT
  10

Bad

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.

Good:

SELECT
  client_id,
  submission_date
FROM
  main_summary
WHERE
  sample_id = '42'
  AND submission_date > '20180101'
LIMIT
  10

Bad:

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:

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:

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:

SELECT client_id, submission_date
FROM main_summary
WHERE
  submission_date > '20180101'
  AND sample_id = '42'
LIMIT 10

Bad

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.
  2. The closing parenthesis should be lined up under the first character of the line that starts the multi-line construct.
  3. The contents of the parentheses should be indented one level.

For example:

Good

WITH sample AS (
  SELECT
    client_id,
  FROM
    main_summary
  WHERE
    sample_id = '42'
)

Bad (Terminating parenthesis on shared line)

WITH sample AS (
  SELECT
    client_id,
  FROM
    main_summary
  WHERE
    sample_id = '42')

Bad (No indent)

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

...
WHERE
  submission_date > 20180101
  AND sample_id = '42'

Bad

...
WHERE
  submission_date > 20180101 AND
  sample_id = '42'

Nested Queries

Do not use nested queries. Instead, use common table expressions to improve readability.

Good:

WITH sample AS (
  SELECT
    client_id,
    submission_date
  FROM
    main_summary
  WHERE
    sample_id = '42'
)

SELECT *
FROM sample
LIMIT 10

Bad:

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.

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