raminqaf commented on code in PR #29311:
URL: https://github.com/apache/flink/pull/29311#discussion_r4152617550
##########
docs/content/docs/sql/reference/data-types.md:
##########
@@ -1677,6 +1678,45 @@ CAST(o AS MAP<STRING, VARIANT>) -- values kept as
variants, the variant null in
CAST(o AS MAP<INT, STRING>) -- fails at validation, a MAP key must be a
character string
```
+A scalar value can also be cast to a `VARIANT` with `CAST` or `TRY_CAST`. Only
a type that a
+`VARIANT` kind holds without loss is supported, and any other type, such as
`INTERVAL`, `RAW`, or
+`BITMAP`, is rejected at validation. The value keeps the kind of its SQL type:
+
+| Input type | Stored `VARIANT` kind
|
+|--------------------------------------------|-------------------------------------------------|
+| `BOOLEAN` | `BOOLEAN`
|
+| `TINYINT`, `SMALLINT`, `INTEGER`, `BIGINT` | `TINYINT`, `SMALLINT`, `INT`,
`BIGINT` |
+| `FLOAT`, `DOUBLE`, `DECIMAL` | `FLOAT`, `DOUBLE`, `DECIMAL`
|
+| `CHAR`, `VARCHAR`, `STRING` | `STRING`
|
+| `BINARY`, `VARBINARY`, `BYTES` | `BYTES`
|
+| `DATE`, `TIME`, `UUID` | `DATE`, `TIME`, `UUID`
|
+| `TIMESTAMP`, `TIMESTAMP_LTZ` | `TIMESTAMP`, `TIMESTAMP_LTZ`
|
+
+- An integer keeps the width of its SQL type, so a `BIGINT` is stored as a
`BIGINT` even when the
+ value would fit a smaller kind. `PARSE_JSON('1')` instead picks the smallest
kind, a `TINYINT`.
+ Either way it casts back to any integer type that holds the value.
+- A character string is stored as a `STRING` and is never parsed. Use
`PARSE_JSON` to parse JSON text.
+- A `TIMESTAMP(p)` or `TIMESTAMP_LTZ(p)` keeps its declared precision. Up to a
precision of 6 it is
+ stored with microseconds, and above with nanoseconds, even when the value
has no digits below a
+ microsecond. Nanoseconds only cover 1677-09-21 to 2262-04-11, so for a
precision above 6 a value
+ outside that range fails the cast, and `TRY_CAST` returns `NULL`.
+- A `NaN` or infinite `FLOAT` or `DOUBLE` is stored as is, although
`PARSE_JSON` rejects them. A
Review Comment:
Agreed. The NaN bullet now says that writing such a value with the `json` or
`raw` format fails the job, as `JSON_STRING` does.
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