# postgresql

This Cursor rule guides PostgreSQL query and schema work, covering naming, joins, data types, and date ranges. Use it when an agent edits SQL across a project.

- rule · `type=rule` · Cursor · ★ 3580
- Author: sanjeed5
- License: CC0-1.0 · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/sanjeed5/awesome-cursor-rules-mdc/tree/HEAD/rules-mdc/postgresql.mdc
- Updated: 2026-05-19
- HTML: https://affpapa.org/en/nevibecode/rules/sanjeed5-postgresql

## What it does

The rule sets conventions for identifiers, query layout, and comments. It calls for explicit joins, favors CTEs over nested subqueries, and recommends replacing `NOT IN` with `NOT EXISTS` or `LEFT JOIN ... IS NULL`. Use `EXPLAIN ANALYZE` to inspect query plans.

Schema guidance covers identity-based `bigint` primary keys, `text` fields, and `numeric` or `decimal` for monetary values. Timestamps should use `timestamptz` in UTC; date ranges should use `>=` and `<`. Its `**/*` glob applies the rule across files, and the caution around `NOT IN` matters when results may contain `NULL`.

## Requirements
- Works with: PostgreSQL

## Install

### Cursor (native platform)

**Manually: put the files in place**
- File: `.cursor/rules/postgresql.mdc` — Frontmatter: description, globs, alwaysApply

### Claude Code

**Manually: put the files in place**
- File: `.claude/rules/postgresql.md` — The paths frontmatter field limits the files: move globs from the source into paths

### Codex

**AGENTS.md**
- Codex reads AGENTS.md: paste the rule text there

### GitHub Copilot

**Manually: put the files in place**
- File: `.github/instructions/postgresql.instructions.md` — The applyTo field sets which files it applies to: move globs from the source into applyTo

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/rules/postgresql.md`

### Cline

**Manually: put the files in place**
- File: `.clinerules/postgresql.md`

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/sanjeed5/awesome-cursor-rules-mdc/tree/HEAD/rules-mdc/postgresql.mdc

## When to use it
- format PostgreSQL queries consistently
- replace implicit table joins with explicit joins
- rewrite nested subqueries as CTEs
- choose data types for IDs, text, and monetary values
- inspect query plans with `EXPLAIN ANALYZE`

## Example prompts
- Rewrite this query to follow the PostgreSQL rule in Cursor.
- Review this migration and use explicit joins instead of selecting every column.
- Check the date range and field types in this PostgreSQL schema.

## Source text · postgresql.mdc · CC0-1.0

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 021abaea414a9ba2.

BEGIN THIRD-PARTY FILE 021abaea414a9ba2
````text
---
description: This guide defines the definitive best practices for writing clean, performant, and maintainable PostgreSQL SQL, focusing on modern conventions and avoiding common pitfalls.
globs: **/*
---
# PostgreSQL Best Practices

This document outlines the mandatory best practices for all PostgreSQL SQL development. Adherence ensures consistency, readability, performance, and maintainability across our codebase.

## 1. Code Organization and Structure

### 1.1. Naming Conventions
Always use `snake_case` for all database identifiers (tables, columns, functions, schemas). SQL keywords must be lowercase. Keep names descriptive but concise.

❌ **BAD**:
```sql
CREATE TABLE UserData (
    UserID INT PRIMARY KEY,
    UserName VARCHAR(255)
);

SELECT UserID, UserName FROM UserData;
```

✅ **GOOD**:
```sql
create table user_data (
    user_id bigint generated always as identity primary key,
    user_name text not null
);

select user_id, user_name from user_data;
```

### 1.2. Formatting
Structure queries for maximum readability. Root keywords (`SELECT`, `FROM`, `WHERE`) belong on their own line, with arguments indented. Use explicit `AS` for all aliases.

❌ **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;
```

✅ **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;
```

### 1.3. Comments
Use block comments (`/* ... */`) for multi-line descriptions and line comments (`--`) for single-line notes.

```sql
/*
This query retrieves active users and their recent orders.
It joins the users table with the orders table.
*/
select
    u.user_id, -- Unique user identifier
    u.user_name,
    o.order_id,
    o.order_date
from
    users as u
inner join
    orders as o
    on u.user_id = o.user_id;
```

## 2. Common Patterns and Anti-patterns

### 2.1. Explicit JOINs
Always use explicit `INNER JOIN`, `LEFT JOIN`, `RIGHT JOIN`, or `FULL JOIN`. Never use implicit joins in the `FROM` clause.

❌ **BAD**:
```sql
select u.user_name, o.order_date from users u, orders o where u.user_id = o.user_id;
```

✅ **GOOD**:
```sql
select
    u.user_name,
    o.order_date
from
    users as u
inner join
    orders as o
    on u.user_id = o.user_id;
```

### 2.2. Common Table Expressions (CTEs)
Prefer CTEs (`WITH` clauses) over nested subqueries for improved readability and modularity.

❌ **BAD**:
```sql
select
    count(*)
from (
    select
        user_id
    from
        orders
    where
        order_date >= '2023-01-01'
    group by
        user_id
    having
        count(*) > 5
) as frequent_buyers;
```

✅ **GOOD**:
```sql
with frequent_buyers as (
    select
        user_id
    from
        orders
    where
        order_date >= '2023-01-01'
    group by
        user_id
    having
        count(*) > 5
)
select
    count(*)
from
    frequent_buyers;
```

### 2.3. Avoid `NOT IN`
Never use `NOT IN` due to its problematic behavior with `NULL` values. Prefer `NOT EXISTS` or `LEFT JOIN ... IS NULL`.

❌ **BAD**:
```sql
select user_name from users where user_id not in (select user_id from orders where status = 'cancelled');
```

✅ **GOOD` (NOT EXISTS)`**:
```sql
select
    user_name
from
    users as u
where not exists (
    select 1 from orders as o where o.user_id = u.user_id and o.status = 'cancelled'
);
```

✅ **GOOD` (LEFT JOIN ... IS NULL)`**:
```sql
select
    u.user_name
from
    users as u
left join
    orders as o
    on u.user_id = o.user_id and o.status = 'cancelled'
where
    o.user_id is null;
```

## 3. Performance Considerations

### 3.1. Explicit Column Selection
Always specify columns explicitly. Avoid `SELECT *` in production code. This improves performance, reduces network traffic, and prevents issues when schema changes.

❌ **BAD**:
```sql
select * from products;
```

✅ **GOOD**:
```sql
````
END THIRD-PARTY FILE 021abaea414a9ba2

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First 4085 of 9091 bytes. © sanjeed5 · CC0-1.0 · https://github.com/sanjeed5/awesome-cursor-rules-mdc/tree/HEAD/rules-mdc/postgresql.mdc

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