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Add support for ClickHouse CSE. #2024

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@pravic pravic commented Sep 8, 2025 •
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https://clickhouse.com/docs/sql-reference/statements/select/with#common-scalar-expressions:

WITH <expression> AS <identifier>

fixes #1514.

  • syntax
  • docs
  • tests
  • Unfortunately, this changes the public API a bit, so requires a version bump.

src/ast/query.rs Outdated
Comment on lines 652 to 666
impl CteOrCse {
pub fn cte(&self) -> Option<&Cte> {
match self {
CteOrCse::Cte(cte) => Some(cte),
CteOrCse::Cse(_) => None,
}
}

pub fn cse(&self) -> Option<&Cse> {
match self {
CteOrCse::Cte(_) => None,
CteOrCse::Cse(cse) => Some(cse),
}
}
}
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Suggested change
impl CteOrCse {
pub fn cte(&self) -> Option<&Cte> {
match self {
CteOrCse::Cte(cte) => Some(cte),
CteOrCse::Cse(_) => None,
}
}
pub fn cse(&self) -> Option<&Cse> {
match self {
CteOrCse::Cte(_) => None,
CteOrCse::Cse(cse) => Some(cse),
}
}
}

I think we can skip this impl, in order to reduce the API surface of the library

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But then we'd need way more changes in the existing code that relies on https://docs.rs/sqlparser/latest/sqlparser/ast/struct.With.html#structfield.cte_tables being Cte. I am on the edge here.

Comment on lines 12263 to 12264
/// Parse a CTE or CSE.
pub fn parse_cte_or_cse(&mut self) -> Result<CteOrCse, ParserError> {
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Suggested change
/// Parse a CTE or CSE.
pubfn parse_cte_or_cse(&mut self) -> Result<CteOrCse, ParserError> {
/// Parse an expression in a `WITH` clause.
fn parse_with_expression(&mut self) -> Result<WithExpression, ParserError> {

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Not pub?

Here there is a suggestion to use a parser method directly (as a solution/workaround for some problem): #713

So, I assumed all/most of Parser methods are/should be available to users.

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For example, currently it's 195 private methods and 322 public methods.

}

/// Parse a CSE (`<expr> AS <ident>`).
pub fn parse_cse(&mut self) -> Result<Cse, ParserError> {
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Suggested change
pubfn parse_cse(&mut self) -> Result<Cse, ParserError> {
fn parse_cse(&mut self) -> Result<Cse, ParserError> {

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Same as above: #2024 (comment)

Comment on lines +609 to +611
fn supports_common_scalar_expressions(&self) -> bool {
false
}
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Should we also add this to the generic dialect? I could not grasp the idea of what expressions should be supported in the generic dialect and what should be not.

For example, supports_select_expr_star isn't listed as supported. Neither is supports_select_exclude.

@pravic pravic requested a review from iffyio September 10, 2025 12:22
Comment on lines +1764 to +1771
// ClickHouse allows these, but not sqlparser
clickhouse()
.parse_sql_statements("WITH foo, bar SELECT 1")
.expect_err("Expected: AS, found: ,");

clickhouse()
.parse_sql_statements("WITH foo(), bar SELECT 1")
.expect_err("Expected: identifier, found: )");
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Interesting: https://fiddle.clickhouse.com/1292850a-31e4-49c7-a309-79bc47a273a2

I am not sure whether it's a feature or a bug in the ClickHouse syntax parser. But since these examples don't make much sense, let's leave them as rejected.

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Clickhouse WITH <expression> AS <identifier> syntax
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