Support @ symbol in column names with backticks and qualified syntax

src/alasqlparser.jison

@@ -269,6 +269,7 @@ SETS                                        	return 'SET'
 'WHILE'                                         return 'WHILE'
 'WITH'                                          return 'WITH'
 'WORK'                                          return 'TRANSACTION'  /* Is this keyword required? */
+
 /* Issue #1173: Reject invalid identifiers like 6minAvgOpac (number followed by letters without space) */
 /* This rule must precede NUMBER to catch invalid patterns before they're tokenized as NUMBER + LITERAL */
 \d+[a-zA-Z_][a-zA-Z_0-9]*						return 'INVALID'
@@ -297,7 +298,6 @@ SETS                                        	return 'SET'
 '!='											return 'NE'
 '('												return 'LPAR'
 ')'												return 'RPAR'
-'@'												return 'AT'
 '{'												return 'LCUR'
 '}'												return 'RCUR'
 
@@ -319,6 +319,7 @@ SETS                                        	return 'SET'
 '~'												return 'TILDA'
 
 [0-9]*[a-zA-Z_]+[a-zA-Z_0-9]* 					return 'LITERAL'
+'@'												return 'AT'
 <<EOF>>               							return 'EOF'
 .												return 'INVALID'
 
@@ -1202,6 +1203,8 @@ Column
 		{ $$ = new yy.Column({columnid: $3, tableid: $1});}
 	| Literal DOT VALUE
 		{ $$ = new yy.Column({columnid: $3, tableid: $1});}
+	| Literal DOT AT Literal
+		{ $$ = new yy.Column({columnid: '@'+$4, tableid: $1});}
 	| Literal
 		{ $$ = new yy.Column({columnid: $1});}
 	;