Support SETTINGS pairs for ClickHouse dialect (#1327)

Co-authored-by: Ifeanyi Ubah <ify1992@yahoo.com>

src/ast/mod.rs

@@ -48,7 +48,7 @@ pub use self::query::{
     MatchRecognizePattern, MatchRecognizeSymbol, Measure, NamedWindowDefinition, NamedWindowExpr,
     NonBlock, Offset, OffsetRows, OrderByExpr, PivotValueSource, Query, RenameSelectItem,
     RepetitionQuantifier, ReplaceSelectElement, ReplaceSelectItem, RowsPerMatch, Select,
-    SelectInto, SelectItem, SetExpr, SetOperator, SetQuantifier, SymbolDefinition, Table,
+    SelectInto, SelectItem, SetExpr, SetOperator, SetQuantifier, Setting, SymbolDefinition, Table,
     TableAlias, TableFactor, TableVersion, TableWithJoins, Top, TopQuantity, ValueTableMode,
     Values, WildcardAdditionalOptions, With,
 };

src/ast/query.rs

@@ -50,6 +50,10 @@ pub struct Query {
     /// `FOR JSON { AUTO | PATH } [ , INCLUDE_NULL_VALUES ]`
     /// (MSSQL-specific)
     pub for_clause: Option<ForClause>,
+    /// ClickHouse syntax: `SELECT * FROM t SETTINGS key1 = value1, key2 = value2`
+    ///
+    /// [ClickHouse](https://clickhouse.com/docs/en/sql-reference/statements/select#settings-in-select-query)
+    pub settings: Option<Vec<Setting>>,
 }
 
 impl fmt::Display for Query {
@@ -70,6 +74,9 @@ impl fmt::Display for Query {
         if !self.limit_by.is_empty() {
             write!(f, " BY {}", display_separated(&self.limit_by, ", "))?;
         }
+        if let Some(ref settings) = self.settings {
+            write!(f, " SETTINGS {}", display_comma_separated(settings))?;
+        }
         if let Some(ref fetch) = self.fetch {
             write!(f, " {fetch}")?;
         }
@@ -828,6 +835,20 @@ impl fmt::Display for ConnectBy {
     }
 }
 
+#[derive(Debug, Clone, PartialEq, PartialOrd, Eq, Ord, Hash)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+#[cfg_attr(feature = "visitor", derive(Visit, VisitMut))]
+pub struct Setting {
+    pub key: Ident,
+    pub value: Value,
+}
+
+impl fmt::Display for Setting {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{} = {}", self.key, self.value)
+    }
+}
+
 /// An expression optionally followed by an alias.
 ///
 /// Example:

src/keywords.rs

@@ -650,6 +650,7 @@ define_keywords!(
     SESSION_USER,
     SET,
     SETS,
+    SETTINGS,
     SHARE,
     SHOW,
     SIMILAR,
@@ -850,6 +851,8 @@ pub const RESERVED_FOR_TABLE_ALIAS: &[Keyword] = &[
     Keyword::FOR,
     // for MYSQL PARTITION SELECTION
     Keyword::PARTITION,
+    // for ClickHouse SELECT * FROM t SETTINGS ...
+    Keyword::SETTINGS,
     // for Snowflake START WITH .. CONNECT BY
     Keyword::START,
     Keyword::CONNECT,

src/parser/mod.rs

@@ -7871,6 +7871,7 @@ impl<'a> Parser<'a> {
                 fetch: None,
                 locks: vec![],
                 for_clause: None,
+                settings: None,
             })
         } else if self.parse_keyword(Keyword::UPDATE) {
             Ok(Query {
@@ -7883,6 +7884,7 @@ impl<'a> Parser<'a> {
                 fetch: None,
                 locks: vec![],
                 for_clause: None,
+                settings: None,
             })
         } else {
             let body = self.parse_boxed_query_body(0)?;
@@ -7928,6 +7930,20 @@ impl<'a> Parser<'a> {
                 vec![]
             };
 
+            let settings = if dialect_of!(self is ClickHouseDialect|GenericDialect)
+                && self.parse_keyword(Keyword::SETTINGS)
+            {
+                let key_values = self.parse_comma_separated(|p| {
+                    let key = p.parse_identifier(false)?;
+                    p.expect_token(&Token::Eq)?;
+                    let value = p.parse_value()?;
+                    Ok(Setting { key, value })
+                })?;
+                Some(key_values)
+            } else {
+                None
+            };
+
             let fetch = if self.parse_keyword(Keyword::FETCH) {
                 Some(self.parse_fetch()?)
             } else {
@@ -7955,6 +7971,7 @@ impl<'a> Parser<'a> {
                 fetch,
                 locks,
                 for_clause,
+                settings,
             })
         }
     }
@@ -9091,6 +9108,7 @@ impl<'a> Parser<'a> {
                     fetch: None,
                     locks: vec![],
                     for_clause: None,
+                    settings: None,
                 }),
                 alias,
             })