Feat: Interpret AS as an operator within CAST function

Changed the interpretation of the AS keyword within the CAST function to be treated as an operator rather than an alias. This ensures that type casting using CAST is handled correctly without confusion between aliases and type conversions.

src/Carbunql.LexicalAnalyzer/Lexer.Expression.cs

@@ -1,5 +1,4 @@
-using System.Diagnostics;
-using System.Diagnostics.CodeAnalysis;
+using System.Diagnostics.CodeAnalysis;
 
 namespace Carbunql.LexicalAnalyzer;
 
@@ -9,7 +8,7 @@ public static partial class Lexer
 
 
 
-    public static IEnumerable<Lex> ReadExpressionLexes(ReadOnlyMemory<char> memory, int position)
+    public static IEnumerable<Lex> ReadExpressionLexes(ReadOnlyMemory<char> memory, int position, Lex? owner = null)
     {
         memory.SkipWhiteSpacesAndComment(ref position);
 
@@ -67,13 +66,15 @@ public static IEnumerable<Lex> ReadExpressionLexes(ReadOnlyMemory<char> memory,
 
                 // operator check
                 memory.SkipWhiteSpacesAndComment(ref position);
+
                 if (TryParseOperator(memory, ref position, out lex))
                 {
                     yield return lex;
                     memory.SkipWhiteSpacesAndComment(ref position);
                     continue;
                 }
 
+
                 // alias, expression separator, or 'from' keyword
                 break;
             }
@@ -97,12 +98,37 @@ public static IEnumerable<Lex> ReadExpressionLexes(ReadOnlyMemory<char> memory,
                     yield return ParseLeftParen(memory, ref position);
 
                     // read arguments
-                    foreach (var argument in ReadExpressionLexes(memory, position))
+                    foreach (var argument in ReadExpressionLexes(memory, position, owner = lex))
                     {
                         yield return argument;
                         position = argument.EndPosition;
                     }
 
+                    memory.SkipWhiteSpacesAndComment(ref position);
+
+                    if (lex.Value.ToLowerInvariant() == "cast")
+                    {
+                        if (memory.TryParseKeywordIgnoreCase(ref position, "as", LexType.Operator, out lex))
+                        {
+                            yield return lex;
+                        }
+                        else
+                        {
+                            throw new FormatException();
+                        }
+
+                        memory.SkipWhiteSpacesAndComment(ref position);
+
+                        if (TryParseDbType(memory, position, out lex, out position))
+                        {
+                            yield return lex;
+                        }
+                        else
+                        {
+                            throw new FormatException();
+                        }
+                    }
+
                     // close paren
                     memory.SkipWhiteSpacesAndComment(ref position);
                     yield return ParseRightParen(memory, ref position);
@@ -178,7 +204,7 @@ public static bool TryParseExpressionName(ReadOnlyMemory<char> memory, ref int p
             {
                 throw new FormatException();
             }
-            lex = new Lex(memory, LexType.Column, start, position - start);
+            lex = new Lex(memory, LexType.Alias, start, position - start);
             return true;
         }
         else
@@ -194,7 +220,7 @@ public static bool TryParseExpressionName(ReadOnlyMemory<char> memory, ref int p
                 return false;
             }
             position = p;
-            lex = new Lex(memory, LexType.Column, start, position - start, name);
+            lex = new Lex(memory, LexType.Alias, start, position - start, name);
             return true;
         }
     }

src/Carbunql.LexicalAnalyzer/Lexer.Operator.StringOperator.cs

@@ -8,7 +8,7 @@ public static partial class Lexer
         "not",
         "and",
         "or",
-        "as", //type cast "as"
+        //"as", //type cast "as"
     };
 
     private static bool TryParseStringOperator(ReadOnlyMemory<char> memory, ref int position, out Lex lex)

src/Carbunql.LexicalAnalyzer/Lexer.Select.cs

@@ -39,7 +39,7 @@ internal static bool TryParseSelect(ReadOnlyMemory<char> memory, ref int positio
         }
 
         // If neither "all" nor "distinct", return simple "select" lex
-        lex = new Lex(memory, LexType.Select, start, position - start);
+        lex = new Lex(memory, LexType.Select, start, position - start, "select");
         return true;
     }
 

test/Carbunql.LexicalAnalyzer.Test/SelectQueryParseTest.cs

@@ -11,9 +11,10 @@ public void Default()
     {
         var text = """
             select
-                a.id,
-                a.value,
-                a.quantity * a.price as total_price
+                a.id
+                , a.value v1
+                , a.value as v2
+                , a.quantity * a.price as total_price
             from
                 table as a
             """;