Implement FROM-first selects (#1713)

src/ast/mod.rs

@@ -68,8 +68,8 @@ pub use self::query::{
     NamedWindowDefinition, NamedWindowExpr, NonBlock, Offset, OffsetRows, OpenJsonTableColumn,
     OrderBy, OrderByExpr, PivotValueSource, ProjectionSelect, Query, RenameSelectItem,
     RepetitionQuantifier, ReplaceSelectElement, ReplaceSelectItem, RowsPerMatch, Select,
-    SelectInto, SelectItem, SelectItemQualifiedWildcardKind, SetExpr, SetOperator, SetQuantifier,
+    SelectFlavor, SelectInto, SelectItem, SelectItemQualifiedWildcardKind, SetExpr, SetOperator,
-    Setting, SymbolDefinition, Table, TableAlias, TableAliasColumnDef, TableFactor,
+    SetQuantifier, Setting, SymbolDefinition, Table, TableAlias, TableAliasColumnDef, TableFactor,
     TableFunctionArgs, TableIndexHintForClause, TableIndexHintType, TableIndexHints,
     TableIndexType, TableSample, TableSampleBucket, TableSampleKind, TableSampleMethod,
     TableSampleModifier, TableSampleQuantity, TableSampleSeed, TableSampleSeedModifier,

src/ast/query.rs

@@ -275,6 +275,19 @@ impl fmt::Display for Table {
     }
 }
 
+/// What did this select look like?
+#[derive(Debug, Clone, PartialEq, PartialOrd, Eq, Ord, Hash)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+#[cfg_attr(feature = "visitor", derive(Visit, VisitMut))]
+pub enum SelectFlavor {
+    /// `SELECT *`
+    Standard,
+    /// `FROM ... SELECT *`
+    FromFirst,
+    /// `FROM *`
+    FromFirstNoSelect,
+}
+
 /// A restricted variant of `SELECT` (without CTEs/`ORDER BY`), which may
 /// appear either as the only body item of a `Query`, or as an operand
 /// to a set operation like `UNION`.
@@ -328,11 +341,23 @@ pub struct Select {
     pub value_table_mode: Option<ValueTableMode>,
     /// STARTING WITH .. CONNECT BY
     pub connect_by: Option<ConnectBy>,
+    /// Was this a FROM-first query?
+    pub flavor: SelectFlavor,
 }
 
 impl fmt::Display for Select {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "SELECT")?;
+        match self.flavor {
+            SelectFlavor::Standard => {
+                write!(f, "SELECT")?;
+            }
+            SelectFlavor::FromFirst => {
+                write!(f, "FROM {} SELECT", display_comma_separated(&self.from))?;
+            }
+            SelectFlavor::FromFirstNoSelect => {
+                write!(f, "FROM {}", display_comma_separated(&self.from))?;
+            }
+        }
 
         if let Some(value_table_mode) = self.value_table_mode {
             write!(f, " {value_table_mode}")?;
@@ -360,7 +385,7 @@ impl fmt::Display for Select {
             write!(f, " {into}")?;
         }
 
-        if !self.from.is_empty() {
+        if self.flavor == SelectFlavor::Standard && !self.from.is_empty() {
             write!(f, " FROM {}", display_comma_separated(&self.from))?;
         }
         if !self.lateral_views.is_empty() {

src/ast/spans.rs

@@ -2077,6 +2077,7 @@ impl Spanned for Select {
             value_table_mode: _,      // todo, BigQuery specific
             connect_by,
             top_before_distinct: _,
+            flavor: _,
         } = self;
 
         union_spans(

src/dialect/clickhouse.rs

@@ -75,4 +75,8 @@ impl Dialect for ClickHouseDialect {
     fn supports_lambda_functions(&self) -> bool {
         true
     }
+
+    fn supports_from_first_select(&self) -> bool {
+        true
+    }
 }

src/dialect/duckdb.rs

@@ -85,4 +85,8 @@ impl Dialect for DuckDbDialect {
     fn supports_array_typedef_size(&self) -> bool {
         true
     }
+
+    fn supports_from_first_select(&self) -> bool {
+        true
+    }
 }

src/dialect/mod.rs

@@ -463,6 +463,17 @@ pub trait Dialect: Debug + Any {
         false
     }
 
+    /// Return true if the dialect supports "FROM-first" selects.
+    ///
+    /// Example:
+    /// ```sql
+    /// FROM table
+    /// SELECT *
+    /// ```
+    fn supports_from_first_select(&self) -> bool {
+        false
+    }
+
     /// Does the dialect support MySQL-style `'user'@'host'` grantee syntax?
     fn supports_user_host_grantee(&self) -> bool {
         false

src/parser/mod.rs

@@ -528,7 +528,7 @@ impl<'a> Parser<'a> {
                 Keyword::DESCRIBE => self.parse_explain(DescribeAlias::Describe),
                 Keyword::EXPLAIN => self.parse_explain(DescribeAlias::Explain),
                 Keyword::ANALYZE => self.parse_analyze(),
-                Keyword::SELECT | Keyword::WITH | Keyword::VALUES => {
+                Keyword::SELECT | Keyword::WITH | Keyword::VALUES | Keyword::FROM => {
                     self.prev_token();
                     self.parse_query().map(Statement::Query)
                 }
@@ -10218,7 +10218,9 @@ impl<'a> Parser<'a> {
     pub fn parse_query_body(&mut self, precedence: u8) -> Result<Box<SetExpr>, ParserError> {
         // We parse the expression using a Pratt parser, as in `parse_expr()`.
         // Start by parsing a restricted SELECT or a `(subquery)`:
-        let expr = if self.peek_keyword(Keyword::SELECT) {
+        let expr = if self.peek_keyword(Keyword::SELECT)
+            || (self.peek_keyword(Keyword::FROM) && self.dialect.supports_from_first_select())
+        {
             SetExpr::Select(self.parse_select().map(Box::new)?)
         } else if self.consume_token(&Token::LParen) {
             // CTEs are not allowed here, but the parser currently accepts them
@@ -10317,6 +10319,39 @@ impl<'a> Parser<'a> {
 
     /// Parse a restricted `SELECT` statement (no CTEs / `UNION` / `ORDER BY`)
     pub fn parse_select(&mut self) -> Result<Select, ParserError> {
+        let mut from_first = None;
+
+        if self.dialect.supports_from_first_select() && self.peek_keyword(Keyword::FROM) {
+            let from_token = self.expect_keyword(Keyword::FROM)?;
+            let from = self.parse_table_with_joins()?;
+            if !self.peek_keyword(Keyword::SELECT) {
+                return Ok(Select {
+                    select_token: AttachedToken(from_token),
+                    distinct: None,
+                    top: None,
+                    top_before_distinct: false,
+                    projection: vec![],
+                    into: None,
+                    from,
+                    lateral_views: vec![],
+                    prewhere: None,
+                    selection: None,
+                    group_by: GroupByExpr::Expressions(vec![], vec![]),
+                    cluster_by: vec![],
+                    distribute_by: vec![],
+                    sort_by: vec![],
+                    having: None,
+                    named_window: vec![],
+                    window_before_qualify: false,
+                    qualify: None,
+                    value_table_mode: None,
+                    connect_by: None,
+                    flavor: SelectFlavor::FromFirstNoSelect,
+                });
+            }
+            from_first = Some(from);
+        }
+
         let select_token = self.expect_keyword(Keyword::SELECT)?;
         let value_table_mode =
             if dialect_of!(self is BigQueryDialect) && self.parse_keyword(Keyword::AS) {
@@ -10371,10 +10406,12 @@ impl<'a> Parser<'a> {
         // otherwise they may be parsed as an alias as part of the `projection`
         // or `from`.
 
-        let from = if self.parse_keyword(Keyword::FROM) {
+        let (from, from_first) = if let Some(from) = from_first.take() {
-            self.parse_table_with_joins()?
+            (from, true)
+        } else if self.parse_keyword(Keyword::FROM) {
+            (self.parse_table_with_joins()?, false)
         } else {
-            vec![]
+            (vec![], false)
         };
 
         let mut lateral_views = vec![];
@@ -10506,6 +10543,11 @@ impl<'a> Parser<'a> {
             qualify,
             value_table_mode,
             connect_by,
+            flavor: if from_first {
+                SelectFlavor::FromFirst
+            } else {
+                SelectFlavor::Standard
+            },
         })
     }
 

tests/sqlparser_clickhouse.rs

@@ -101,6 +101,7 @@ fn parse_map_access_expr() {
             qualify: None,
             value_table_mode: None,
             connect_by: None,
+            flavor: SelectFlavor::Standard,
         },
         select
     );

tests/sqlparser_common.rs

@@ -461,6 +461,7 @@ fn parse_update_set_from() {
                             window_before_qualify: false,
                             value_table_mode: None,
                             connect_by: None,
+                            flavor: SelectFlavor::Standard,
                         }))),
                         order_by: None,
                         limit: None,
@@ -5289,6 +5290,7 @@ fn test_parse_named_window() {
         window_before_qualify: true,
         value_table_mode: None,
         connect_by: None,
+        flavor: SelectFlavor::Standard,
     };
     assert_eq!(actual_select_only, expected);
 }
@@ -5915,6 +5917,7 @@ fn parse_interval_and_or_xor() {
             window_before_qualify: false,
             value_table_mode: None,
             connect_by: None,
+            flavor: SelectFlavor::Standard,
         }))),
         order_by: None,
         limit: None,
@@ -8022,6 +8025,7 @@ fn lateral_function() {
         window_before_qualify: false,
         value_table_mode: None,
         connect_by: None,
+        flavor: SelectFlavor::Standard,
     };
     assert_eq!(actual_select_only, expected);
 }
@@ -8919,6 +8923,7 @@ fn parse_merge() {
                             qualify: None,
                             value_table_mode: None,
                             connect_by: None,
+                            flavor: SelectFlavor::Standard,
                         }))),
                         order_by: None,
                         limit: None,
@@ -10703,6 +10708,7 @@ fn parse_unload() {
                     qualify: None,
                     value_table_mode: None,
                     connect_by: None,
+                    flavor: SelectFlavor::Standard,
                 }))),
                 with: None,
                 limit: None,
@@ -10913,6 +10919,7 @@ fn parse_connect_by() {
                 ))))),
             }],
         }),
+        flavor: SelectFlavor::Standard,
     };
 
     let connect_by_1 = concat!(
@@ -10997,6 +11004,7 @@ fn parse_connect_by() {
                     ))))),
                 }],
             }),
+            flavor: SelectFlavor::Standard,
         }
     );
 
@@ -11860,6 +11868,7 @@ fn test_extract_seconds_ok() {
             window_before_qualify: false,
             value_table_mode: None,
             connect_by: None,
+            flavor: SelectFlavor::Standard,
         }))),
         order_by: None,
         limit: None,
@@ -13592,3 +13601,65 @@ fn test_lambdas() {
     );
     dialects.verified_expr("transform(array(1, 2, 3), x -> x + 1)");
 }
+
+#[test]
+fn test_select_from_first() {
+    let dialects = all_dialects_where(|d| d.supports_from_first_select());
+    let q1 = "FROM capitals";
+    let q2 = "FROM capitals SELECT *";
+
+    for (q, flavor, projection) in [
+        (q1, SelectFlavor::FromFirstNoSelect, vec![]),
+        (
+            q2,
+            SelectFlavor::FromFirst,
+            vec![SelectItem::Wildcard(WildcardAdditionalOptions::default())],
+        ),
+    ] {
+        let ast = dialects.verified_query(q);
+        let expected = Query {
+            with: None,
+            body: Box::new(SetExpr::Select(Box::new(Select {
+                select_token: AttachedToken::empty(),
+                distinct: None,
+                top: None,
+                projection,
+                top_before_distinct: false,
+                into: None,
+                from: vec![TableWithJoins {
+                    relation: table_from_name(ObjectName::from(vec![Ident {
+                        value: "capitals".to_string(),
+                        quote_style: None,
+                        span: Span::empty(),
+                    }])),
+                    joins: vec![],
+                }],
+                lateral_views: vec![],
+                prewhere: None,
+                selection: None,
+                group_by: GroupByExpr::Expressions(vec![], vec![]),
+                cluster_by: vec![],
+                distribute_by: vec![],
+                sort_by: vec![],
+                having: None,
+                named_window: vec![],
+                window_before_qualify: false,
+                qualify: None,
+                value_table_mode: None,
+                connect_by: None,
+                flavor,
+            }))),
+            order_by: None,
+            limit: None,
+            offset: None,
+            fetch: None,
+            locks: vec![],
+            limit_by: vec![],
+            for_clause: None,
+            settings: None,
+            format_clause: None,
+        };
+        assert_eq!(expected, ast);
+        assert_eq!(ast.to_string(), q);
+    }
+}

tests/sqlparser_duckdb.rs

@@ -288,6 +288,7 @@ fn test_select_union_by_name() {
                 qualify: None,
                 value_table_mode: None,
                 connect_by: None,
+                flavor: SelectFlavor::Standard,
             }))),
             right: Box::<SetExpr>::new(SetExpr::Select(Box::new(Select {
                 select_token: AttachedToken::empty(),
@@ -317,6 +318,7 @@ fn test_select_union_by_name() {
                 qualify: None,
                 value_table_mode: None,
                 connect_by: None,
+                flavor: SelectFlavor::Standard,
             }))),
         });
         assert_eq!(ast.body, expected);

tests/sqlparser_mssql.rs

@@ -137,6 +137,7 @@ fn parse_create_procedure() {
                     qualify: None,
                     value_table_mode: None,
                     connect_by: None,
+                    flavor: SelectFlavor::Standard,
                 })))
             }))],
             params: Some(vec![
@@ -1114,6 +1115,7 @@ fn parse_substring_in_select() {
                         window_before_qualify: false,
                         value_table_mode: None,
                         connect_by: None,
+                        flavor: SelectFlavor::Standard,
                     }))),
                     order_by: None,
                     limit: None,
@@ -1251,6 +1253,7 @@ fn parse_mssql_declare() {
                     qualify: None,
                     value_table_mode: None,
                     connect_by: None,
+                    flavor: SelectFlavor::Standard,
                 })))
             }))
         ],

tests/sqlparser_mysql.rs

@@ -1111,6 +1111,7 @@ fn parse_escaped_quote_identifiers_with_escape() {
                 window_before_qualify: false,
                 value_table_mode: None,
                 connect_by: None,
+                flavor: SelectFlavor::Standard,
             }))),
             order_by: None,
             limit: None,
@@ -1164,6 +1165,7 @@ fn parse_escaped_quote_identifiers_with_no_escape() {
                 window_before_qualify: false,
                 value_table_mode: None,
                 connect_by: None,
+                flavor: SelectFlavor::Standard,
             }))),
             order_by: None,
             limit: None,
@@ -1211,6 +1213,7 @@ fn parse_escaped_backticks_with_escape() {
                 window_before_qualify: false,
                 value_table_mode: None,
                 connect_by: None,
+                flavor: SelectFlavor::Standard,
             }))),
             order_by: None,
             limit: None,
@@ -1262,6 +1265,7 @@ fn parse_escaped_backticks_with_no_escape() {
                 window_before_qualify: false,
                 value_table_mode: None,
                 connect_by: None,
+                flavor: SelectFlavor::Standard,
             }))),
             order_by: None,
             limit: None,
@@ -1931,6 +1935,7 @@ fn parse_select_with_numeric_prefix_column_name() {
                     window_before_qualify: false,
                     value_table_mode: None,
                     connect_by: None,
+                    flavor: SelectFlavor::Standard,
                 })))
             );
         }
@@ -1983,6 +1988,7 @@ fn parse_select_with_concatenation_of_exp_number_and_numeric_prefix_column() {
                     window_before_qualify: false,
                     value_table_mode: None,
                     connect_by: None,
+                    flavor: SelectFlavor::Standard,
                 })))
             );
         }
@@ -2503,6 +2509,7 @@ fn parse_substring_in_select() {
                         qualify: None,
                         value_table_mode: None,
                         connect_by: None,
+                        flavor: SelectFlavor::Standard,
                     }))),
                     order_by: None,
                     limit: None,
@@ -2799,6 +2806,7 @@ fn parse_hex_string_introducer() {
                 value_table_mode: None,
                 into: None,
                 connect_by: None,
+                flavor: SelectFlavor::Standard,
             }))),
             order_by: None,
             limit: None,

tests/sqlparser_postgres.rs

@@ -1315,6 +1315,7 @@ fn parse_copy_to() {
                     qualify: None,
                     value_table_mode: None,
                     connect_by: None,
+                    flavor: SelectFlavor::Standard,
                 }))),
                 order_by: None,
                 limit: None,
@@ -2666,6 +2667,7 @@ fn parse_array_subquery_expr() {
                         window_before_qualify: false,
                         value_table_mode: None,
                         connect_by: None,
+                        flavor: SelectFlavor::Standard,
                     }))),
                     right: Box::new(SetExpr::Select(Box::new(Select {
                         select_token: AttachedToken::empty(),
@@ -2688,6 +2690,7 @@ fn parse_array_subquery_expr() {
                         window_before_qualify: false,
                         value_table_mode: None,
                         connect_by: None,
+                        flavor: SelectFlavor::Standard,
                     }))),
                 }),
                 order_by: None,