ClickHouse: Allow $ inside identifiers

fuzz/fuzz_seeds/clickhouse_2686_dollar_identifier.sql

@@ -0,0 +1 @@
+SELECT a$b, c$$, d$e$, $$text$$, $tag$text$tag$ FROM t$1 WHERE x$y = 1

src/dialect/clickhouse.rs

@@ -29,7 +29,9 @@ impl Dialect for ClickHouseDialect {
     }
 
     fn is_identifier_part(&self, ch: char) -> bool {
-        self.is_identifier_start(ch) || ch.is_ascii_digit()
+        // Undocumented, but the server accepts `$` in identifiers for MySQL compatibility
+        // since https://github.com/ClickHouse/ClickHouse/pull/14232
+        self.is_identifier_start(ch) || ch.is_ascii_digit() || ch == '$'
     }
 
     /// ClickHouse accepts both backticks and double quotes, but its own

tests/sqlparser_clickhouse.rs

@@ -2366,6 +2366,30 @@ fn parse_update_on_cluster_and_settings() {
     );
 }
 
+#[test]
+fn parse_dollar_in_identifier() {
+    let select = clickhouse_and_generic().verified_only_select("SELECT a$b, c$$, d$e$ FROM t");
+    assert_eq!(
+        select.projection,
+        vec![
+            UnnamedExpr(Identifier(Ident::new("a$b"))),
+            UnnamedExpr(Identifier(Ident::new("c$$"))),
+            UnnamedExpr(Identifier(Ident::new("d$e$"))),
+        ]
+    );
+    // Dollar-quoted strings still take precedence at the start of a token.
+    clickhouse_and_generic().verified_stmt("SELECT $$abc$$, $tag$abc$tag$");
+    // Tokenizes like ClickHouse does; only the parser rejects it.
+    let err = clickhouse()
+        .parse_sql_statements("INSERT I$$$$$$$$$$$$$$$$$$$$$$$$$$")
+        .unwrap_err();
+    assert!(matches!(err, ParserError(_)), "{err}");
+
+    all_dialects_where(|d| !d.is_identifier_part('$'))
+        .parse_sql_statements("SELECT a$b FROM t")
+        .unwrap_err();
+}
+
 fn clickhouse() -> TestedDialects {
     TestedDialects::new(vec![Box::new(ClickHouseDialect {})])
 }