chore: decimal padding

[BobdenOs]

decimal test

The goal of this PR is to identify how others handle Decimal columns.

The conclusion is that the current behavior of padding Decimal columns to their defined scale is the standard.

entity number {
  ...
  decimal   : cds.Decimal(5, 4);
}

await INSERT([
  { decimal: 1.0 },
  { decimal: 0.1 },
  { decimal: 9 },
]).into(number)

const result = await cds.run(`SELECT decimal, cast(decimal as ${cds.requires.db.impl === '@cap-js/hana' ? 'nvarchar' : 'text'}) as string FROM ${number}`)

All databases pad their decimal numbers. Even SQLite3 does as 1.0 could have been 1. It is important to keep in mind that SQLite3 doesn't have a scale setting for their real data type. There for the scale of a real is still showing in the string result as >0. Where an integer has in implicit scale of 0.

HANA

hana-client [
  { DECIMAL: '1.0000', STRING: '1.0000' },
  { DECIMAL: '0.1000', STRING: '0.1000' },
  { DECIMAL: '9.0000', STRING: '9.0000' }
]

hdb [
  { DECIMAL: '1.0000', STRING: '1.0000' },
  { DECIMAL: '0.1000', STRING: '0.1000' },
  { DECIMAL: '9.0000', STRING: '9.0000' }
]

Postgres

pg [
  { decimal: '1.0000', string: '1.0000' },
  { decimal: '0.1000', string: '0.1000' },
  { decimal: '9.0000', string: '9.0000' }
]

SQLite3

in SQLite3 real doesn't have a scale

node:sqlite [
  [Object: null prototype] { decimal: 1, string: '1.0' },
  [Object: null prototype] { decimal: 0.1, string: '0.1' },
  [Object: null prototype] { decimal: 9, string: '9.0' }
]
better-sqlite3 [
  { decimal: 1, string: '1.0' },
  { decimal: 0.1, string: '0.1' },
  { decimal: 9, string: '9.0' }
]
sql.js [
  { decimal: 1, string: '1.0' },
  { decimal: 0.1, string: '0.1' },
  { decimal: 9, string: '9.0' }
]

CAP java

# default
{
  "@context": "$metadata#literals_number",
  "@metadataEtag": "W/\"c72c5a00be9537eedd1442260745701d7d9f650d6c0130980629e7672af0bf94\"",
  "value": [
    { "decimal": 1.0000 },
    { "decimal": 0.1000 }
  ]
}
# Accept:'application/json;IEEE754Compatible=true'
{
  "@context": "$metadata#literals_number",
  "@metadataEtag": "W/\"c72c5a00be9537eedd1442260745701d7d9f650d6c0130980629e7672af0bf94\"",
  "value": [
    { "decimal": "1.0000" },
    { "decimal": "0.1000" }
  ]
}