Add lateral derived support

Author: thomas-jeepe

src/sqlast/query.rs

@@ -209,6 +209,7 @@ pub enum TableFactor {
         with_hints: Vec<ASTNode>,
     },
     Derived {
+        lateral: bool,
         subquery: Box<SQLQuery>,
         alias: Option<SQLIdent>,
     },
@@ -235,8 +236,16 @@ impl ToString for TableFactor {
                 }
                 s
             }
-            TableFactor::Derived { subquery, alias } => {
-                let mut s = format!("({})", subquery.to_string());
+            TableFactor::Derived {
+                lateral,
+                subquery,
+                alias,
+            } => {
+                let mut s = String::new();
+                if *lateral {
+                    s += "LATERAL ";
+                }
+                s += &format!("({})", subquery.to_string());
                 if let Some(alias) = alias {
                     s += &format!(" AS {}", alias);
                 }

src/sqlparser.rs

@@ -1390,11 +1390,18 @@ impl Parser {
 
     /// A table name or a parenthesized subquery, followed by optional `[AS] alias`
     pub fn parse_table_factor(&mut self) -> Result<TableFactor, ParserError> {
+        let lateral = self.parse_keyword("LATERAL");
         if self.consume_token(&Token::LParen) {
             let subquery = Box::new(self.parse_query()?);
             self.expect_token(&Token::RParen)?;
             let alias = self.parse_optional_alias(keywords::RESERVED_FOR_TABLE_ALIAS)?;
-            Ok(TableFactor::Derived { subquery, alias })
+            Ok(TableFactor::Derived {
+                lateral,
+                subquery,
+                alias,
+            })
+        } else if lateral {
+            self.expected("subquery after LATERAL", self.peek_token())
         } else {
             let name = self.parse_object_name()?;
             // Postgres, MSSQL: table-valued functions:

tests/sqlparser_common.rs

@@ -1390,6 +1390,50 @@ fn parse_fetch_variations() {
     );
 }
 
+#[test]
+fn lateral_derived() {
+    fn chk(lateral_in: bool) {
+        let lateral_str = if lateral_in { "LATERAL " } else { "" };
+        let sql = format!(
+            "SELECT * FROM customer LEFT JOIN {}\
+             (SELECT * FROM order WHERE order.customer = customer.id LIMIT 3) AS order ON true",
+            lateral_str
+        );
+        let select = verified_only_select(&sql);
+        assert_eq!(select.joins.len(), 1);
+        assert_eq!(
+            select.joins[0].join_operator,
+            JoinOperator::LeftOuter(JoinConstraint::On(ASTNode::SQLValue(Value::Boolean(true))))
+        );
+        if let TableFactor::Derived {
+            lateral,
+            ref subquery,
+            ref alias,
+        } = select.joins[0].relation
+        {
+            assert_eq!(lateral_in, lateral);
+            assert_eq!(Some("order".to_string()), *alias);
+            assert_eq!(
+                subquery.to_string(),
+                "SELECT * FROM order WHERE order.customer = customer.id LIMIT 3"
+            );
+        } else {
+            unreachable!()
+        }
+    }
+    chk(false);
+    chk(true);
+
+    let sql = "SELECT * FROM customer LEFT JOIN LATERAL generate_series(1, customer.id)";
+    let res = parse_sql_statements(sql);
+    assert_eq!(
+        ParserError::ParserError(
+            "Expected subquery after LATERAL, found: generate_series".to_string()
+        ),
+        res.unwrap_err()
+    );
+}
+
 #[test]
 #[should_panic(
     expected = "Parse results with GenericSqlDialect are different from PostgreSqlDialect"