vtgate executor: route "show create table" to the user-provided or vs…

…chema-indicated keyspace

Previously the sql parser treated everything after `CREATE TABLE` as opaque.
This change updates the sql parser to look at the create table argument
to help direct queries to the appropriate keyspace.

Signed-off-by: David Weitzman <dweitzman@pinterest.com>

go/vt/sqlparser/ast.go

@@ -1517,6 +1517,7 @@ func (f *ForeignKeyDefinition) walkSubtree(visit Visit) error {
 type Show struct {
 	Type                   string
 	OnTable                TableName
+	Table                  TableName
 	ShowTablesOpt          *ShowTablesOpt
 	Scope                  string
 	ShowCollationFilterOpt *Expr
@@ -1547,13 +1548,22 @@ func (node *Show) Format(buf *TrackedBuffer) {
 	if node.Type == "collation" && node.ShowCollationFilterOpt != nil {
 		buf.Myprintf(" where %v", *node.ShowCollationFilterOpt)
 	}
+	if node.HasTable() {
+		buf.Myprintf(" %v", node.Table)
+	}
 }
 
 // HasOnTable returns true if the show statement has an "on" clause
 func (node *Show) HasOnTable() bool {
 	return node.OnTable.Name.v != ""
 }
 
+// HasTable returns true if the show statement has a parsed table name.
+// Not all show statements parse table names.
+func (node *Show) HasTable() bool {
+	return node.Table.Name.v != ""
+}
+
 func (node *Show) walkSubtree(visit Visit) error {
 	return nil
 }

go/vt/sqlparser/parse_test.go

@@ -1107,7 +1107,7 @@ var (
 		output: "show create procedure",
 	}, {
 		input:  "show create table t",
-		output: "show create table",
+		output: "show create table t",
 	}, {
 		input:  "show create trigger t",
 		output: "show create trigger",