ClickHouse: Support unparenthesized IN right-hand side

src/dialect/clickhouse.rs

@@ -80,6 +80,11 @@ impl Dialect for ClickHouseDialect {
         true
     }
 
+    // See <https://clickhouse.com/docs/sql-reference/operators/in>
+    fn supports_in_unparenthesized_expr(&self) -> bool {
+        true
+    }
+
     /// See <https://clickhouse.com/docs/en/sql-reference/functions#higher-order-functions---operator-and-lambdaparams-expr-function>
     fn supports_lambda_functions(&self) -> bool {
         true

src/dialect/mod.rs

@@ -435,6 +435,12 @@ pub trait Dialect: Debug + Any {
         false
     }
 
+    /// Returns true if the dialect supports a bare expression as the right-hand
+    /// side of `IN`, without a parenthesized list — as in `x IN 'a'`.
+    fn supports_in_unparenthesized_expr(&self) -> bool {
+        false
+    }
+
     /// Returns true if the dialect supports `BEGIN {DEFERRED | IMMEDIATE | EXCLUSIVE | TRY | CATCH} [TRANSACTION]` statements
     fn supports_start_transaction_modifier(&self) -> bool {
         false
@@ -2051,6 +2057,10 @@ mod tests {
                 self.0.supports_in_empty_list()
             }
 
+            fn supports_in_unparenthesized_expr(&self) -> bool {
+                self.0.supports_in_unparenthesized_expr()
+            }
+
             fn convert_type_before_value(&self) -> bool {
                 self.0.convert_type_before_value()
             }

src/parser/mod.rs

@@ -4392,6 +4392,15 @@ impl<'a> Parser<'a> {
                 negated,
             });
         }
+        if self.dialect.supports_in_unparenthesized_expr()
+            && self.peek_token_ref().token != Token::LParen
+        {
+            return Ok(Expr::InList {
+                expr: Box::new(expr),
+                list: vec![self.parse_expr()?],
+                negated,
+            });
+        }
         self.expect_token(&Token::LParen)?;
         let in_op = match self.maybe_parse(|p| p.parse_query())? {
             Some(subquery) => Expr::InSubquery {

tests/sqlparser_clickhouse.rs

@@ -1846,6 +1846,29 @@ fn parse_inner_array_join() {
     }
 }
 
+#[test]
+fn parse_in_unparenthesized_expr() {
+    // IN [expr] parses to IN ([expr]) and does not cause regressions
+    clickhouse().expr_parses_to("x IN 'a'", "x IN ('a')");
+
+    // The branch must not fire when the next token is `(` (regressions).
+    clickhouse().verified_expr("x IN (1, 2, 3)");
+    clickhouse().verified_stmt("SELECT * FROM t WHERE x IN (SELECT y FROM u)");
+}
+
+#[test]
+fn parse_in_unparenthesized_dictionary_placeholder() {
+    // IN [{placeholder:Type}] parses to IN ({placholder:Type})
+    clickhouse().expr_parses_to("x IN {ids:Array(UInt64)}", "x IN ({ids: Array(UInt64)})");
+    clickhouse().expr_parses_to(
+        "x NOT IN {ids:Array(UInt64)}",
+        "x NOT IN ({ids: Array(UInt64)})",
+    );
+    clickhouse().verified_expr("x IN ({ids: Array(UInt64)})");
+    // Precedence: the trailing `AND` is not swallowed.
+    clickhouse().verified_expr("x IN ({p: Array(UInt64)}) AND y = 1");
+}
+
 fn clickhouse() -> TestedDialects {
     TestedDialects::new(vec![Box::new(ClickHouseDialect {})])
 }

tests/sqlparser_common.rs

@@ -2375,15 +2375,45 @@ fn parse_in_unnest() {
 
 #[test]
 fn parse_in_error() {
-    // <expr> IN <expr> is no valid
+    // <expr> IN <expr> is no valid, except in dialects that accept an
+    // unparenthesized expression as the IN right-hand side (e.g. ClickHouse).
     let sql = "SELECT * FROM customers WHERE segment in segment";
-    let res = parse_sql_statements(sql);
+    let res =
+        all_dialects_except(|d| d.supports_in_unparenthesized_expr()).parse_sql_statements(sql);
     assert_eq!(
         ParserError::ParserError("Expected: (, found: segment".to_string()),
         res.unwrap_err()
     );
 }
 
+#[test]
+fn parse_in_unparenthesized_expr() {
+    // Dialects supporting an unparenthesized IN right-hand side wrap a bare expression
+    // into a single-element list (e.g. `x IN 'a'` -> `x IN ('a')`).
+    let dialects = all_dialects_where(|d| d.supports_in_unparenthesized_expr());
+    dialects.expr_parses_to("x IN 'a'", "x IN ('a')");
+
+    // The branch must not fire when the next token is `(` (regressions).
+    dialects.verified_expr("x IN (1, 2, 3)");
+    dialects.verified_stmt("SELECT * FROM t WHERE x IN (SELECT y FROM u)");
+}
+
+#[test]
+fn parse_in_unparenthesized_dictionary_placeholder() {
+    // The `{name:Type}` placeholder form additionally requires dictionary syntax.
+    let dialects = all_dialects_where(|d| {
+        d.supports_in_unparenthesized_expr() && d.supports_dictionary_syntax()
+    });
+    dialects.expr_parses_to("x IN {ids:Array(UInt64)}", "x IN ({ids: Array(UInt64)})");
+    dialects.expr_parses_to(
+        "x NOT IN {ids:Array(UInt64)}",
+        "x NOT IN ({ids: Array(UInt64)})",
+    );
+    dialects.verified_expr("x IN ({ids: Array(UInt64)})");
+    // Precedence: the trailing `AND` is not swallowed.
+    dialects.verified_expr("x IN ({p: Array(UInt64)}) AND y = 1");
+}
+
 #[test]
 fn parse_string_agg() {
     let sql = "SELECT a || b";
@@ -10834,8 +10864,11 @@ fn parse_position() {
 
 #[test]
 fn parse_position_negative() {
+    // Dialects that accept an unparenthesized IN right-hand side (e.g. ClickHouse)
+    // report a different error here, so exclude them.
     let sql = "SELECT POSITION(foo IN) from bar";
-    let res = parse_sql_statements(sql);
+    let res =
+        all_dialects_except(|d| d.supports_in_unparenthesized_expr()).parse_sql_statements(sql);
     assert_eq!(
         ParserError::ParserError("Expected: (, found: )".to_string()),
         res.unwrap_err()