Issue Creation Checklist

• I understand that my issue will be automatically closed if I don't fill in the requested information.
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Bug Description

When defining a column with unique: true (either via the @unique decorator or directly in the @column options), Sequelize keeps creating duplicate unique constraints on the same column each time sequelize.sync({ alter: true }) runs.

Instead of detecting that the constraint already exists, Sequelize creates new constraints with incremented names like:

• social_media_name_key
• social_media_name_key1
• social_media_name_key2
• social_media_name_key3

This results in multiple redundant unique constraints being attached to the same column.

Reproducible Example

import {
  Table,
  Column,
  Model,
  DataType,
} from "sequelize-typescript";

@Table({ tableName: "social_media" })
export class SocialMedia extends Model {
  @Column({ type: DataType.STRING(30), unique: true, allowNull: false })
  name!: string;
}

After running sequelize.sync({ alter: true }) multiple times, the table accumulates duplicate constraints:

social_media_name_key
social_media_name_key1
social_media_name_key2
...

What do you expect to happen?

Sequelize should recognize that the unique constraint is already present and not add duplicates.

What is actually happening?

Sequelize generates a new unique constraint with an incremented name on each sync, leading to clutter in the schema.

Environment

• Sequelize version: 6.37.7
• Node.js version: 22.17.1
• TypeScript version: 5.8.3
• Database & Version: PostgreSQL Server 17
• Connector library & Version: pg 8.16.0

Would you be willing to resolve this issue by submitting a Pull Request?

• Yes, I have the time and I know how to start.
• Yes, I have the time but I will need guidance.
• No, I don't have the time, but my company or I are supporting Sequelize through donations on OpenCollective
• No, I don't have the time, and I understand that I will need to wait until someone from the community or maintainers is interested in resolving my issue.