Description

tomershay

opened on Jul 12, 2026

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Failing SQL Feature

ClickHouse supports parametric (constructor-style) data types as the target of a CAST, including nested ones such as Nullable(Decimal(10, 2)). Here Decimal(10, 2) declares a decimal with precision 10 and scale 2, and Nullable(...) wraps it so the column can also hold NULL. JSQLParser fails to parse this type expression when it is used as the target type of a CAST(... AS ...).

See the ClickHouse docs:

• https://clickhouse.com/docs/en/sql-reference/data-types/nullable
• https://clickhouse.com/docs/en/sql-reference/data-types/decimal

Full SQL Example

CREATE TABLE cast_demo (id UInt32, x Float64) ENGINE = MergeTree ORDER BY id;
INSERT INTO cast_demo (id, x) VALUES (1, 10.5), (2, 3.14159), (3, 1234567.891), (4, 0);
SELECT CAST(x AS Nullable(Decimal(10, 2))) FROM cast_demo;

Parsing Error

ParseException: Encountered: <OPENING_BRACKET> / "(", at line 3, column 25, in lexical state DEFAULT.
Was expecting one of these terminals within expansion starting at 9127:5:
    <K_FORMAT> (inside 9125:5) ...
    <CLOSING_BRACKET> (inside 9127:5) 

Tested with ClickHouse version: 25.8

Activity

1. fudianchn commented on Aug 7, 2026

   

   fudianchn

   on Aug 7, 2026

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   Thanks for the report. The root cause is that the argument production of ColDataType only accepted atomic tokens (numbers, string literals, bare identifiers/keywords), so a nested parametric type such as Decimal(10, 2) inside Nullable(...) was rejected at its inner (.

   Opened #2451 to allow an argument that is itself a parametric type (DATA_TYPE or identifier immediately followed by an argument list) to be parsed as a nested ColDataType. SELECT CAST(x AS Nullable(Decimal(10, 2))) FROM cast_demo and LowCardinality(Decimal(10, 2)) now parse and round-trip; the full test suite (4647 tests) passes with no regressions.
2. manticore-projects

   closed this as completedin 3997ba4on Aug 7, 2026
3. pull

   added a commit that references this issue on Aug 7, 2026

   fix: support nested parametric data types as CAST target (JSQLParser#…

   This issue will close once commit 3997ba4 is merged into the 'master' branch.

   3997ba4

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