callicles opened a new issue, #2153:
URL: https://github.com/apache/datafusion-sqlparser-rs/issues/2153
## Problem
ClickHouse data types are case-sensitive and require PascalCase (e.g.,
`String`, `Int32`, `Nullable`). However, the `sqlparser-rs` library's `Display`
implementation for `DataType` converts certain types to uppercase, causing
`UNKNOWN_TYPE` errors when round-tripping SQL through ClickHouse.
## Example
```rust
use sqlparser::dialect::ClickHouseDialect;
use sqlparser::parser::Parser;
let sql = "CREATE TABLE t (col Nullable(String))";
let dialect = ClickHouseDialect {};
let ast = Parser::parse_sql(&dialect, sql).unwrap();
// Round-trip: parse and convert back to string
let regenerated = ast[0].to_string();
// Result: "CREATE TABLE t (col Nullable(STRING))"
// ^^^^^^ uppercase! When this
regenerated SQL is executed against ClickHouse, it fails with:
```
```
Code: 47. DB::Exception: Unknown type STRING. (UNKNOWN_TYPE)
```
## Affected Types
| Type | Current Output | ClickHouse Requires |
|------|----------------|---------------------|
| `DataType::Int8` | `INT8` | `Int8` |
| `DataType::Int64` | `INT64` | `Int64` |
| `DataType::Float64` | `FLOAT64` | `Float64` |
| `DataType::String` | `STRING` | `String` |
| `DataType::Bool` | `BOOL` | `Bool` |
| `DataType::Date` | `DATE` | `Date` |
| `DataType::Datetime` | `DATETIME` | `DateTime` |
**Types already correct (PascalCase):**
- `Int16`, `Int32`, `Int128`, `Int256`
- `UInt8`, `UInt16`, `UInt32`, `UInt64`, `UInt128`, `UInt256`
- `Float32`
- `Nullable`, `LowCardinality`, `Array`, `Map`, `Tuple`, `Nested`
## Root Cause
The `Display` trait implementation for `DataType` uses uppercase for type
names (e.g., `write!(f, "STRING")`), which is standard for most SQL dialects
but incorrect for ClickHouse.
The challenge is that `Display` doesn't have access to dialect context, so
it can't conditionally format based on the active dialect.
## Proposed Solution
Add a dialect-aware formatting method to `DataType`:
1. Add a `requires_pascalcase_types()` method to the `Dialect` trait
(returns `false` by default, `true` for `ClickHouseDialect`)
2. Add a `to_sql(&dyn Dialect)` method to `DataType` that respects the
dialect's casing requirements
3. Keep the existing `Display` implementation unchanged for backwards
compatibility
```rust
// In src/dialect/mod.rs
pub trait Dialect {
fn requires_pascalcase_types(&self) -> bool { false }
// ...
}
// In src/dialect/clickhouse.rs
impl Dialect for ClickHouseDialect {
fn requires_pascalcase_types(&self) -> bool { true }
}
// In src/ast/data_type.rs
impl DataType {
pub fn to_sql(&self, dialect: &dyn Dialect) -> String {
// Format with PascalCase if dialect requires it
}
}
```
## Workarounds
Currently, users must post-process the SQL string output to fix casing. See
[514-labs/moosestack#3152](https://github.com/514-labs/moosestack/pull/3152)
for an example regex-based workaround.
## References
- [ClickHouse Data Types
Documentation](https://clickhouse.com/docs/en/sql-reference/data-types)
- Related workaround:
[514-labs/moosestack#3152](https://github.com/514-labs/moosestack/pull/3152)
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