raminqaf commented on code in PR #28758:
URL: https://github.com/apache/flink/pull/28758#discussion_r3628460514
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docs/content.zh/docs/sql/reference/data-types.md:
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@@ -1507,19 +1507,62 @@ close to the semantics of JSON. Compared to `ROW` and
`STRUCTURED` type, `VARIAN
flexibility to support highly nested and evolving schema.
`VARIANT` allows for deeply nested data structures, such as arrays within
arrays, maps within maps,
-or combinations of both.This capability makes `VARIANT` ideal for scenarios
where data complexity
+or combinations of both. This capability makes `VARIANT` ideal for scenarios
where data complexity
and nesting are significant.
`VARIANT` allows schema evolution, enabling the storage of data with changing
or unknown schemas
without requiring upfront schema definition. For example, if a new field is
added to the data, it
can be directly incorporated into the `VARIANT` data without modifying the
table schema. This is
particularly useful in dynamic environments where schemas may evolve over time.
+A `VARIANT` stores a single value of one of the following kinds: `NULL`,
`BOOLEAN`, `TINYINT`,
+`SMALLINT`, `INT`, `BIGINT`, `FLOAT`, `DOUBLE`, `DECIMAL` (up to precision
38), `STRING`, `DATE`,
+`TIMESTAMP`, `TIMESTAMP_LTZ`, `BYTES`, or a nested array or object.
`TIMESTAMP` and `TIMESTAMP_LTZ`
+are stored with microsecond precision and `DATE` as a day count. There is no
`TIME` kind.
+
+The `PARSE_JSON` function produces only the kinds that JSON syntax can express:
+
+| JSON input | Stored `VARIANT` kind
|
+|-----------------------------------------------------|-------------------------------------------------|
+| `null` | `NULL`
|
+| `true` / `false` | `BOOLEAN`
|
+| Integer within the 64-bit signed range | smallest of
`TINYINT`/`SMALLINT`/`INT`/`BIGINT` |
+| Integer beyond 64-bit, up to 38 significant digits | `DECIMAL`
|
+| Decimal in plain notation, up to precision/scale 38 | `DECIMAL`
|
+| Number in scientific notation, e.g. `1.5e3` | `DOUBLE`
|
+| Number exceeding 38 digits of precision or scale | `DOUBLE`
|
+| String | `STRING`
|
+| Array | array (elements
encoded by the same rules) |
+| Object | object (values encoded
by the same rules) |
+
+Because JSON has no literal for float, date, timestamp, or binary values,
`PARSE_JSON` never
+produces `FLOAT`, `DATE`, `TIMESTAMP`, `TIMESTAMP_LTZ`, or `BYTES`. A
`VARIANT` can still hold
+those kinds when built by other producers, such as the programmatic
`VariantBuilder` API or format
+conversions like Avro.
+
+The JSON specification has no `NaN` or infinity literals, so
`PARSE_JSON('NaN')`,
+`PARSE_JSON('Infinity')`, and `PARSE_JSON('-Infinity')` fail, and
`TRY_PARSE_JSON` returns `NULL`.
+A `VARIANT` has no dedicated kind for these values. To keep one, store it as a
JSON string and cast
+it back out, for example `CAST(CAST(PARSE_JSON('"Infinity"') AS STRING) AS
FLOAT)`.
+
A primitive-valued `VARIANT` can be converted to a scalar type with `CAST` or
`TRY_CAST`. Numeric
-targets are lenient: a variant holding any numeric value casts to any numeric
type, so a JSON integer
-such as `PARSE_JSON('42')` casts to `INT` or `BIGINT`. Other targets require
the stored value to be of
-the matching kind. When the value cannot be converted, `CAST` fails the job
and `TRY_CAST` returns
-`NULL`. Use the `JSON_STRING` function to obtain the JSON string
representation of a `VARIANT`.
+targets accept any numeric value, so `PARSE_JSON('42')` casts to `INT`,
`BIGINT`, or `DOUBLE`. A
+value outside an integer or `DECIMAL` target's range fails `CAST` and returns
`NULL` for
+`TRY_CAST`. Other targets require the stored value to be of the matching kind,
and a mismatch is
+handled the same way. Casting a `VARIANT` to `CHAR`/`VARCHAR` extracts the
scalar value, so a
+stored string is returned unquoted (for example `foo`), while objects and
arrays return their JSON
Review Comment:
For objects, arrays, bytes we rely on the `Variant#toJson()` implementation.
All other types (i.e., String) we convert to literal String. This is because
for a case like `CAST(PARSE_JSON('foo') AS STRING))` we want to return a string
literal `foo` and not a JSON String `"foo"`.
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