sql-patternslisted
Install: claude install-skill aiskillstore/marketplace
# SQL Patterns
Quick reference for common SQL patterns.
## CTE (Common Table Expressions)
```sql
WITH active_users AS (
SELECT id, name, email
FROM users
WHERE status = 'active'
)
SELECT * FROM active_users WHERE created_at > '2024-01-01';
```
### Chained CTEs
```sql
WITH
active_users AS (
SELECT id, name FROM users WHERE status = 'active'
),
user_orders AS (
SELECT user_id, COUNT(*) as order_count
FROM orders GROUP BY user_id
)
SELECT u.name, COALESCE(o.order_count, 0) as orders
FROM active_users u
LEFT JOIN user_orders o ON u.id = o.user_id;
```
## Window Functions (Quick Reference)
| Function | Use |
|----------|-----|
| `ROW_NUMBER()` | Unique sequential numbering |
| `RANK()` | Rank with gaps (1, 2, 2, 4) |
| `DENSE_RANK()` | Rank without gaps (1, 2, 2, 3) |
| `LAG(col, n)` | Previous row value |
| `LEAD(col, n)` | Next row value |
| `SUM() OVER` | Running total |
| `AVG() OVER` | Moving average |
```sql
SELECT
date,
revenue,
LAG(revenue, 1) OVER (ORDER BY date) as prev_day,
SUM(revenue) OVER (ORDER BY date) as running_total
FROM daily_sales;
```
## JOIN Reference
| Type | Returns |
|------|---------|
| `INNER JOIN` | Only matching rows |
| `LEFT JOIN` | All left + matching right |
| `RIGHT JOIN` | All right + matching left |
| `FULL JOIN` | All rows, NULL where no match |
## Pagination
```sql
-- OFFSET/LIMIT (simple, slow for large offsets)
SELECT * FROM products ORDER BY id LIMIT 20 OFFSET