Add SQL style guide as Cursor rule

- Add comprehensive SQL style guide from postgres.ai as Cursor rule
- Rule applies to *.sql and *.psql files
- Includes formatting guidelines, best practices, and examples
- Update .gitignore to exclude only environment.json, keep rules tracked

Author: NikolayS

.cursor/rules/sql-style.mdc

@@ -0,0 +1,136 @@
+---
+globs: *.sql,*.psql
+description: SQL style guide rules for PostgreSQL development
+---
+
+# SQL style guide
+
+Source: [postgres.ai SQL style guide](https://postgres.ai/rules/sql-style)
+
+## Core philosophy
+
+From PEP8: 
+
+* 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
+
+## Core rules
+
+* **Use lowercase SQL keywords** (not uppercase)
+* Use `snake_case` for all identifiers (no CamelCase)
+* Names must begin with a letter and may not end in underscore
+* Only use letters, numbers, and underscores in names
+* Be explicit: always use `AS` for aliases, specify JOIN types
+* Root keywords on their own line (except with single argument)
+* Multi-line arguments must be indented relative to root keyword
+* Use **ISO 8601 date format**: `yyyy-mm-ddThh:mm:ss.sssss`
+* Foreign key naming: `user_id` to reference `users` table (singular + \_id)
+* Use meaningful aliases that reflect the data (not just single letters)
+
+## Formatting
+
+### Keywords and alignment
+
+```sql
+-- Root keywords left-aligned
+-- Arguments indented relative to root keyword
+select
+  client_id,
+  submission_date
+from main_summary
+where
+  sample_id = '42'
+  and submission_date > '20180101'
+limit 10;
+```
+
+### Comments
+
+```sql
+/* Block comments for multi-line descriptions */
+-- Line comments for single line notes
+select
+  client_id,  -- user identifier
+  submission_date
+from main_summary;
+```
+
+### Parentheses
+
+```sql
+-- Opening paren ends the line
+-- Closing paren aligns with starting line
+-- Contents indented
+with sample as (
+  select
+    client_id,
+    submission_date
+  from main_summary
+  where sample_id = '42'
+)
+```
+
+### Boolean operators
+
+```sql
+-- AND/OR at beginning of line
+where
+  submission_date > '20180101'
+  and sample_id = '42'
+```
+
+## Table design rules
+
+* Always add `id` column of type `identity generated always`
+* Always add table comments using `comment on table...`
+* Default to `public` schema
+* Include schema in queries for clarity
+* Use singular table names with `_id` suffix for foreign keys
+
+## Best practices
+
+* Use CTEs instead of nested queries
+* Explicit column names in GROUP BY (except for expressions - see below)
+* Functions treated as identifiers: `date_trunc()` not `DATE_TRUNC()`
+* One argument per line for multi-argument clauses
+* Use meaningful aliases that reflect the data being selected
+
+### GROUP BY exception
+
+```sql
+-- Acceptable: use numbers to avoid repeating complex expressions
+select
+  date_trunc('minute', xact_start) as xact_start_minute,
+  count(*)
+from pg_stat_activity
+group by 1
+order by 1;
+```
+
+## Examples
+
+### Good
+
+```sql
+select
+  t.client_id as client_id,
+  date(t.created_at) as day
+from telemetry as t
+inner join users as u
+  on t.user_id = u.id
+where
+  t.submission_date > '2019-07-01'
+  and t.sample_id = '10'
+group by t.client_id, day;
+```
+
+### Bad
+
+```sql
+SELECT t.client_id, DATE(t.created_at) day
+FROM telemetry t, users u
+WHERE t.user_id = u.id AND t.submission_date > '2019-07-01'
+GROUP BY 1, 2;
+```

.gitignore

@@ -1,2 +1,3 @@
 .DS_Store
+.cursor/environment.json