fix: parse unions (#329)

Author: juleswritescode

crates/pgt_statement_splitter/src/parser.rs

@@ -147,6 +147,7 @@ impl Parser {
     }
 
     /// Look ahead to the next relevant token
+    /// Returns `None` if we are already at the last relevant token
     fn look_ahead(&self) -> Option<&Token> {
         // we need to look ahead to the next relevant token
         let mut look_ahead_pos = self.next_pos + 1;
@@ -161,6 +162,7 @@ impl Parser {
         }
     }
 
+    /// Returns `None` if there are no previous relevant tokens
     fn look_back(&self) -> Option<&Token> {
         // we need to look back to the last relevant token
         let mut look_back_pos = self.next_pos - 1;

crates/pgt_statement_splitter/src/parser/common.rs

@@ -145,6 +145,12 @@ pub(crate) fn unknown(p: &mut Parser, exclude: &[SyntaxKind]) {
                         SyntaxKind::Also,
                         // for create rule
                         SyntaxKind::Instead,
+                        // for UNION
+                        SyntaxKind::Union,
+                        // for UNION ALL
+                        SyntaxKind::All,
+                        // for UNION ... EXCEPT
+                        SyntaxKind::Except,
                     ]
                     .iter()
                     .all(|x| Some(x) != prev.as_ref())

crates/pgt_statement_splitter/tests/data/simple_union__4.sql

@@ -0,0 +1,7 @@
+select 1 union all select 2;
+
+select 1 union select 2;
+
+select 1 union select 2 except select 3;
+
+select 1 union all select 2 except select 3;