Decimals lose precision (postgres)

Bug description

The decimals sent to Postgres by the query engine lose precision

How to reproduce

run this script:

import { PrismaClient } from '@prisma/client'
import { Decimal } from '@prisma/client/runtime'
const prisma = new PrismaClient()

const run = async () => {
  const value = new Decimal('600.780000000012345678912345678912')
  console.log('before', { foo: value })
  const foo = await prisma.foo.create({
    data: {
      amountDecimal: value,
      amountString: value.toString(),
    },
  })
  console.log('after', { foo })
}
run()

Expected behaviour

I expect amountDecimal: 600.7800000006123456789 not 600.7800000006123,

Prisma information

model Foo {
  id                 String      @id @default(uuid())
  amountDecimal      Decimal  @db.Decimal(65, 30)
  amountString       String
}

SQL Table generated:

CREATE TABLE "Foo" (
    "id" TEXT NOT NULL,
    "amountDecimal" DECIMAL(65,30) NOT NULL,
    "amountString" TEXT NOT NULL,

    PRIMARY KEY ("id")
);

Environment & setup

prisma               : 2.21.2
@prisma/client       : 2.21.2
Current platform     : darwin
Query Engine         : query-engine e421996c87d5f3c8f7eeadd502d4ad402c89464d (at node_modules/@prisma/engines/query-engine-darwin)
Migration Engine     : migration-engine-cli e421996c87d5f3c8f7eeadd502d4ad402c89464d (at node_modules/@prisma/engines/migration-engine-darwin)
Introspection Engine : introspection-core e421996c87d5f3c8f7eeadd502d4ad402c89464d (at node_modules/@prisma/engines/introspection-engine-darwin)
Format Binary        : prisma-fmt e421996c87d5f3c8f7eeadd502d4ad402c89464d (at node_modules/@prisma/engines/prisma-fmt-darwin)
Default Engines Hash : e421996c87d5f3c8f7eeadd502d4ad402c89464d
Studio               : 0.371.0

[matthewmueller]

We’ll be tackling this in #6902

[janpio]

For internal bookkeeping: This was considered a duplicate of https://github.com/prisma/prisma/issues/5925