Only check for DISTINCT AS together and for BigQuery

Author: bombsimon

src/parser/mod.rs

@@ -11505,46 +11505,37 @@ impl<'a> Parser<'a> {
         }
 
         let select_token = self.expect_keyword(Keyword::SELECT)?;
-        let distinct_pre_as = self.parse_all_or_distinct()?;
-
-        let value_table_mode =
-            if dialect_of!(self is BigQueryDialect) && self.parse_keyword(Keyword::AS) {
+        let value_table_mode = if dialect_of!(self is BigQueryDialect) {
+            if self.parse_keywords(&[Keyword::DISTINCT, Keyword::AS]) {
                 if self.parse_keyword(Keyword::VALUE) {
-                    if distinct_pre_as.is_some() {
-                        Some(ValueTableMode::DistinctAsValue)
-                    } else {
-                        Some(ValueTableMode::AsValue)
-                    }
+                    Some(ValueTableMode::DistinctAsValue)
                 } else if self.parse_keyword(Keyword::STRUCT) {
-                    if distinct_pre_as.is_some() {
-                        Some(ValueTableMode::DistinctAsStruct)
-                    } else {
-                        Some(ValueTableMode::AsStruct)
-                    }
+                    Some(ValueTableMode::DistinctAsStruct)
+                } else {
+                    self.expected("VALUE or STRUCT", self.peek_token())?
+                }
+            } else if self.parse_keyword(Keyword::AS) {
+                if self.parse_keyword(Keyword::VALUE) {
+                    Some(ValueTableMode::AsValue)
+                } else if self.parse_keyword(Keyword::STRUCT) {
+                    Some(ValueTableMode::AsStruct)
                 } else {
                     self.expected("VALUE or STRUCT", self.peek_token())?
                 }
             } else {
                 None
-            };
+            }
+        } else {
+            None
+        };
 
         let mut top_before_distinct = false;
         let mut top = None;
         if self.dialect.supports_top_before_distinct() && self.parse_keyword(Keyword::TOP) {
             top = Some(self.parse_top()?);
             top_before_distinct = true;
         }
-
-        // If we parsed a `DISTINCT` value before checking `ValueTableMode` and it is set to some,
-        // but we didn't have an `AS`, this is the initial `DISTINCT` value in the `SELECT` and
-        // should be re-used.
-        // If we don't have a `DISTINCT` parsed or if it was consumed for the `ValueTableMode` we
-        // look for `DISTINCT` again.
-        let distinct = if value_table_mode.is_none() && distinct_pre_as.is_some() {
-            distinct_pre_as
-        } else {
-            self.parse_all_or_distinct()?
-        };
+        let distinct = self.parse_all_or_distinct()?;
         if !self.dialect.supports_top_before_distinct() && self.parse_keyword(Keyword::TOP) {
             top = Some(self.parse_top()?);
         }