[jira] [Comment Edited] (CALCITE-5212) Attempting to create a Decimal with scale specified but precision not specified results in Decimal with scale 0

["Ian Bertolacci (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CALCITE-5212?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17936895#comment-17936895 ] 

Ian Bertolacci edited comment on CALCITE-5212 at 3/19/25 5:27 PM:
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[This has popped up again.|https://lists.apache.org/thread/3ry69b60nqo1923kzyl18122hchcpfsp]

>  I think it might actually be possible for a scale other than zero to be returned if a Decimal with non-zero scale and unspecified precision has been created before the Decimal with zero scale and unspecified precision has been created.

I discovered that this is true. The first created type is the type returned on subsequent invocations.


was (Author: ian.bertolacci):
This has popped up again.

>  I think it might actually be possible for a scale other than zero to be returned if a Decimal with non-zero scale and unspecified precision has been created before the Decimal with zero scale and unspecified precision has been created.

I discovered that this is true. The first created type is the type returned on subsequent invocations.

> Attempting to create a Decimal with scale specified but precision not specified results in Decimal with scale 0
> ---------------------------------------------------------------------------------------------------------------
>
>                 Key: CALCITE-5212
>                 URL: https://issues.apache.org/jira/browse/CALCITE-5212
>             Project: Calcite
>          Issue Type: Bug
>    Affects Versions: 1.30.0
>            Reporter: Ian Bertolacci
>            Priority: Minor
>
> (Frankly, I'm not sure if there is really any need to change this behavior, as scale without precision is a very odd case that doesn't really make a lot of sense in the larger picture (the system we're building on top of uses precision to mean digits _before_ the decimal-point and not the total number of digits, and we're still playing around with if and how that should be expressed in Calcite's type-system), but I'm still writing this out anyways just in-case it is of interest to anyone or if someone else encounters this behavior and want's an explanation.)
>  
> {{`RelDataTypeFactoryImpl.createSqlType(SqlTypeName.DECIMAL, RelDataType.PRECISION_NOT_SPECIFIED, 5)`}} could be expected to create a Decimal with scale 5.
> However it instead creates a Decimal with scale 0.†
> This happens because:
>  # RelDataType does not include scale in its digest if precision is not specified.
> Thus: Two Decimal types with different scales but no precision have *the same* digest.
>  # RelDataType uses the digest to compute a hash code.
> Thus: Two Decimal types with different scales but no precision have *the same* hash code.
>  # {{`RelDataTypeFactoryImpl.canonize(RelDataType)`}} is used to look up a type in {{`DATATYPE_CACHE`}} which uses the hash code as the key.
> Thus: Two Decimal types with different scales but no precision *will collide* in the cache.
>  #  There is no check in RelDataTypeFactoryImpl or SqlTypeFactoryImpl's canonize method to assert that the type returned from the cache actually matches the type given as a parameter.
> Thus: If the parameter type matches a type in the cache, the cache'd type will *always* be returned, even if it the two types are different.
>  # RelDataTypeFactoryImpl and its child classes (such as SqlTypeFactoryImpl) all use the result canonize *at the end* of the type creation functions (such as createSqlType) as the result of the function.
> Thus: If the function creates an intermediate Decimal type with scale but no precision, the result of the function will be whatever that intermediate type matches with in the cache, which could have any scale.
> † I think it might actually be possible for a scale other than zero to be returned if a Decimal with non-zero scale and unspecified precision has been created before the Decimal with zero scale and unspecified precision has been created.



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