Merge pull request ClickHouse#41095 from evillique/from-select

Add 'FROM table SELECT column' syntax

src/Parsers/ParserSelectQuery.cpp

@@ -108,6 +108,13 @@ bool ParserSelectQuery::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)
         }
     }
 
+    /// FROM database.table or FROM table or FROM (subquery) or FROM tableFunction(...)
+    if (s_from.ignore(pos, expected))
+    {
+        if (!ParserTablesInSelectQuery(false).parse(pos, tables, expected))
+            return false;
+    }
+
     /// SELECT [ALL/DISTINCT [ON (expr_list)]] [TOP N [WITH TIES]] expr_list
     {
         bool has_all = false;
@@ -166,7 +173,7 @@ bool ParserSelectQuery::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)
     }
 
     /// FROM database.table or FROM table or FROM (subquery) or FROM tableFunction(...)
-    if (s_from.ignore(pos, expected))
+    if (!tables && s_from.ignore(pos, expected))
     {
         if (!ParserTablesInSelectQuery().parse(pos, tables, expected))
             return false;

src/Parsers/ParserTablesInSelectQuery.cpp

@@ -21,9 +21,9 @@ bool ParserTableExpression::parseImpl(Pos & pos, ASTPtr & node, Expected & expec
 {
     auto res = std::make_shared<ASTTableExpression>();
 
-    if (!ParserWithOptionalAlias(std::make_unique<ParserSubquery>(), true).parse(pos, res->subquery, expected)
-        && !ParserWithOptionalAlias(std::make_unique<ParserFunction>(false, true), true).parse(pos, res->table_function, expected)
-        && !ParserWithOptionalAlias(std::make_unique<ParserCompoundIdentifier>(true, true), true)
+    if (!ParserWithOptionalAlias(std::make_unique<ParserSubquery>(), allow_alias_without_as_keyword).parse(pos, res->subquery, expected)
+        && !ParserWithOptionalAlias(std::make_unique<ParserFunction>(false, true), allow_alias_without_as_keyword).parse(pos, res->table_function, expected)
+        && !ParserWithOptionalAlias(std::make_unique<ParserCompoundIdentifier>(true, true), allow_alias_without_as_keyword)
                 .parse(pos, res->database_and_table_name, expected))
         return false;
 
@@ -126,7 +126,7 @@ bool ParserTablesInSelectQueryElement::parseImpl(Pos & pos, ASTPtr & node, Expec
 
     if (is_first)
     {
-        if (!ParserTableExpression().parse(pos, res->table_expression, expected))
+        if (!ParserTableExpression(allow_alias_without_as_keyword).parse(pos, res->table_expression, expected))
             return false;
     }
     else if (ParserArrayJoin().parse(pos, res->array_join, expected))
@@ -200,7 +200,7 @@ bool ParserTablesInSelectQueryElement::parseImpl(Pos & pos, ASTPtr & node, Expec
                 return false;
         }
 
-        if (!ParserTableExpression().parse(pos, res->table_expression, expected))
+        if (!ParserTableExpression(allow_alias_without_as_keyword).parse(pos, res->table_expression, expected))
             return false;
 
         if (table_join->kind != JoinKind::Comma
@@ -261,12 +261,12 @@ bool ParserTablesInSelectQuery::parseImpl(Pos & pos, ASTPtr & node, Expected & e
 
     ASTPtr child;
 
-    if (ParserTablesInSelectQueryElement(true).parse(pos, child, expected))
+    if (ParserTablesInSelectQueryElement(true, allow_alias_without_as_keyword).parse(pos, child, expected))
         res->children.emplace_back(child);
     else
         return false;
 
-    while (ParserTablesInSelectQueryElement(false).parse(pos, child, expected))
+    while (ParserTablesInSelectQueryElement(false, allow_alias_without_as_keyword).parse(pos, child, expected))
         res->children.emplace_back(child);
 
     node = res;

src/Parsers/ParserTablesInSelectQuery.h

@@ -12,33 +12,49 @@ struct ASTTableJoin;
   */
 class ParserTablesInSelectQuery : public IParserBase
 {
+public:
+    explicit ParserTablesInSelectQuery(bool allow_alias_without_as_keyword_ = true)
+        : allow_alias_without_as_keyword(allow_alias_without_as_keyword_) {}
+
 protected:
     const char * getName() const override { return "table, table function, subquery or list of joined tables"; }
     bool parseImpl(Pos & pos, ASTPtr & node, Expected & expected) override;
+
+private:
+    bool allow_alias_without_as_keyword;
 };
 
 
 class ParserTablesInSelectQueryElement : public IParserBase
 {
 public:
-    explicit ParserTablesInSelectQueryElement(bool is_first_) : is_first(is_first_) {}
+    explicit ParserTablesInSelectQueryElement(bool is_first_, bool allow_alias_without_as_keyword_ = true)
+        : is_first(is_first_), allow_alias_without_as_keyword(allow_alias_without_as_keyword_) {}
 
 protected:
     const char * getName() const override { return "table, table function, subquery or list of joined tables"; }
     bool parseImpl(Pos & pos, ASTPtr & node, Expected & expected) override;
 
 private:
     bool is_first;
+    bool allow_alias_without_as_keyword;
 
     static void parseJoinStrictness(Pos & pos, ASTTableJoin & table_join);
 };
 
 
 class ParserTableExpression : public IParserBase
 {
+public:
+    explicit ParserTableExpression(bool allow_alias_without_as_keyword_ = true)
+        : allow_alias_without_as_keyword(allow_alias_without_as_keyword_) {}
+
 protected:
     const char * getName() const override { return "table or subquery or table function"; }
     bool parseImpl(Pos & pos, ASTPtr & node, Expected & expected) override;
+
+private:
+    bool allow_alias_without_as_keyword;
 };
 
 

tests/queries/0_stateless/02417_from_select_syntax.reference

@@ -0,0 +1,4 @@
+0
+0
+0
+0

tests/queries/0_stateless/02417_from_select_syntax.sql

@@ -0,0 +1,4 @@
+FROM numbers(1) SELECT number;
+WITH 1 as n FROM numbers(1) SELECT number * n;
+FROM (FROM numbers(1) SELECT *) SELECT number;
+FROM (FROM numbers(1) SELECT *) AS select SELECT number;