Support PostgreSQL array subquery constructor (#566)

src/ast/mod.rs

@@ -376,6 +376,8 @@ pub enum Expr {
     /// A parenthesized subquery `(SELECT ...)`, used in expression like
     /// `SELECT (subquery) AS x` or `WHERE (subquery) = x`
     Subquery(Box<Query>),
+    /// An array subquery constructor, e.g. `SELECT ARRAY(SELECT 1 UNION SELECT 2)`
+    ArraySubquery(Box<Query>),
     /// The `LISTAGG` function `SELECT LISTAGG(...) WITHIN GROUP (ORDER BY ...)`
     ListAgg(ListAgg),
     /// The `GROUPING SETS` expr.
@@ -573,6 +575,7 @@ impl fmt::Display for Expr {
                 subquery
             ),
             Expr::Subquery(s) => write!(f, "({})", s),
+            Expr::ArraySubquery(s) => write!(f, "ARRAY({})", s),
             Expr::ListAgg(listagg) => write!(f, "{}", listagg),
             Expr::GroupingSets(sets) => {
                 write!(f, "GROUPING SETS (")?;

src/parser.rs

@@ -449,11 +449,18 @@ impl<'a> Parser<'a> {
                 Keyword::TRIM => self.parse_trim_expr(),
                 Keyword::INTERVAL => self.parse_literal_interval(),
                 Keyword::LISTAGG => self.parse_listagg_expr(),
-                // Treat ARRAY[1,2,3] as an array [1,2,3], otherwise try as function call
+                // Treat ARRAY[1,2,3] as an array [1,2,3], otherwise try as subquery or a function call
                 Keyword::ARRAY if self.peek_token() == Token::LBracket => {
                     self.expect_token(&Token::LBracket)?;
                     self.parse_array_expr(true)
                 }
+                Keyword::ARRAY
+                    if self.peek_token() == Token::LParen
+                        && !dialect_of!(self is ClickHouseDialect) =>
+                {
+                    self.expect_token(&Token::LParen)?;
+                    self.parse_array_subquery()
+                }
                 Keyword::NOT => self.parse_not(),
                 // Here `w` is a word, check if it's a part of a multi-part
                 // identifier, a function call, or a simple identifier:
@@ -927,6 +934,13 @@ impl<'a> Parser<'a> {
         }
     }
 
+    // Parses an array constructed from a subquery
+    pub fn parse_array_subquery(&mut self) -> Result<Expr, ParserError> {
+        let query = self.parse_query()?;
+        self.expect_token(&Token::RParen)?;
+        Ok(Expr::ArraySubquery(Box::new(query)))
+    }
+
     /// Parse a SQL LISTAGG expression, e.g. `LISTAGG(...) WITHIN GROUP (ORDER BY ...)`.
     pub fn parse_listagg_expr(&mut self) -> Result<Expr, ParserError> {
         self.expect_token(&Token::LParen)?;