[BUG]: decimal fields serialize to number (instead of string) when added in a with query

[carderne]

Report hasn't been filed before.

• I have verified that the bug I'm about to report hasn't been filed before.

What version of drizzle-orm are you using?

0.38.2

What version of drizzle-kit are you using?

0.30.1

Other packages

No response

Describe the Bug

Summary

If you have a Postgres column with type decimal(), it is correctly serialised to type string in JavaScript.

However, if you load a referenced table that has a decimal column, it is incorrectly serialised to type number in JavaScript.

Full reproduction

This is the issue:

// query.ts
import { db } from "./db";
import * as schema from "./schema";

const [parent] = await db.insert(schema.parent).values({ parentVal: "12.34" }).returning();
await db.insert(schema.child).values({ parentId: parent?.id, childVal: "56.78" });
const res = await db.query.child.findFirst({ with: { parent: true } });

console.log(typeof res?.childVal);         // === "string" ✅
console.log(typeof res?.parent.parentVal); // === "number" ❌

Setup code used here:

// schema.ts
import { relations } from "drizzle-orm";
import { decimal, pgTable, serial } from "drizzle-orm/pg-core";

export const parent = pgTable("parent", {
  id: serial().primaryKey(),
  parentVal: decimal(),
});
export const child = pgTable("child", {
  parentId: serial().references(() => parent.id),
  childVal: decimal(),
});
export const childRelations = relations(child, ({ one }) => ({
  parent: one(parent, {
    fields: [child.parentId],
    references: [parent.id],
  }),
}));

// db.ts
import { drizzle } from "drizzle-orm/node-postgres";
import pg from "pg";
import * as schema from "./schema";

export const DATABASE_URL = "postgres://...";
const client = new pg.Pool({ connectionString: DATABASE_URL });
export const db = drizzle({ schema, client });