# MySQL ERROR 1066 (42000): Not unique table/alias: 'x'

**Code:** `1066` · **Category:** SQL · **Seen on:** SQL

The same table or alias appears twice in a FROM/JOIN without distinct aliases.

## Meaning

Self-joins and repeated joins need different aliases. ORMs joining the same relation twice can produce this.

## Common causes

- Self-join without aliases
- Joining the same table twice
- ORM eager loads duplicating joins

## Quick fix

1. Give each occurrence its own alias (u1, u2)
2. Check ORM eager-loading config if the SQL is generated

## Detailed fix by platform

### SQL

1. `SELECT e.name, m.name AS manager FROM employees e JOIN employees m ON m.id = e.manager_id;`

## How to diagnose

1. **Alias** — Which name repeats?
2. **Recent change** — Did it start after a deploy, upgrade, or configuration change? Compare with the last working version.

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Source: [WhatIsMyError](https://whatismyerror.com/errors/sql/not-unique-table-alias)