The SQL style guide

The goal of this style guide is to improve the readability of SQL queries.

Formatting

Keywords

Keywords should be UPPERCASE.

/* Good */
SELECT COUNT(1) FROM tablename WHERE 1;

/* Bad */
select count(1) from tablename where 1;

Names

Named objects should not be surrounded by backticks, no matter what MySQL says when it dumps the table structure for you.
- If you need to use backticks because of something in your table name, rename your table.

Indentation and newlines

Newlines should be used for any query that is at all complex or longer than 72 characters.

Each clause should begin a new line. SELECT, JOIN, LEFT JOIN, OUTER JOIN, WHERE, UNION, etc. are keywords that begin new clauses.

  /* Good */
  SELECT COUNT(1)
    FROM tablename
   WHERE really_loooong_column = CONCAT(other_column, ' street');

  /* Bad */
  SELECT COUNT(1) FROM tablename WHERE really_loooong_column = CONCAT(other_column, ' street');

The keywords that begin a clause should be right-aligned. The idea is to make a single character column between the keywords and their objects.

  /* Good */
  SELECT COUNT(1)
    FROM tablename
   WHERE 1;

    SELECT key_column, COUNT(1)
      FROM tablename
  GROUP BY key_column;

  /* Bad */
  SELECT COUNT(1)
  FROM tablename
  WHERE 1;

Subqueries should be aligned as though the open parenthesis were the 0-column So, they should be indented as a unit, to identify them as subqueries. They should continue to have the opening keywords right-aligned.

  /* Good */
  SELECT *
    FROM (  SELECT candidates.name, count(1)
              FROM candidates
              JOIN votes ON candidates.id = votes.candidate_id
          GROUP BY candidates.name) name_count
    JOIN city c ON name_count.name = c.mayor;

  /* Bad */
  SELECT *
    FROM (SELECT candidates.name, count(1)
      FROM candidates
      JOIN votes ON candidates.id = votes.candidate_id
      GROUP BY candidates.name) name_count
    JOIN city ON name_count.name = city.mayor;

Structure

Column aliases should always use the keyword AS This becomes significant when a query has several columns selected with columns aliased. Without the AS keyword, a dropped comma makes two columns become a single aliased column.
```
  /* Good */
  SELECT ebe_ebs_sox_flag_set_for_all_crs AS sox_ok
    FROM tablename;

  /* Bad */
  SELECT ebe_ebs_sox_flag_set_for_all_crs sox_ok
    FROM tablename;
```
Table aliases and column aliases should be descriptive. Much like variable names, "a", "b", "x", etc are not generally useful in and of themselves outside of short examples.
Tiny names for table aliases can sometimes work as abbreviations. As an example, if "releases" is referenced frequently, it might make sense to abbreviate it "r". However, "rel" is almost as short, and much more descriptive. Have a good reason for "r" instead of "rel".

Subquery aliases should be even more descriptive. Subqueries effectively create ad-hoc tables in memory. As such, if you name it "x", then there's absolutely nothing to suggest the intention behind the table to a later maintainer.

/* Good */
SELECT *
  FROM (SELECT table1.id AS child, 
               table2.id AS parent
          FROM table1
          JOIN table2 ON (table2.parent_id = table1.id) ) parentage;

/* Bad */
SELECT *
  FROM (SELECT table1.id AS child, 
               table2.id AS parent
          FROM table1
          JOIN table2 ON (table2.parent_id = table1.id) ) x;

/* Bad */
SELECT *
  FROM (SELECT table1.id AS child, 
               table2.id AS parent
          FROM table1
          JOIN table2 ON (table2.parent_id = table1.id) ) link;