allow select without table to support cross apply

Author: mnsrulz

QueryBuilder.Tests/SelectTests.cs

@@ -803,5 +803,40 @@ public void EscapeClauseThrowsForMultipleCharacters()
                     .HavingContains("Column1", @"TestString\%", false, @"\aa");
             });
         }
+
+
+        [Fact]
+        public void BasicSelectRaw_WithNoTable()
+        {
+            var q = new Query().SelectRaw("somefunction() as c1");                
+
+            var c = Compilers.CompileFor(EngineCodes.SqlServer, q);
+            Assert.Equal("SELECT somefunction() as c1", c.ToString());
+        }
+
+        [Fact]
+        public void BasicSelect_WithNoTable()
+        {
+            var q = new Query().Select("c1");
+            var c = Compilers.CompileFor(EngineCodes.SqlServer, q);
+            Assert.Equal("SELECT [c1]", c.ToString());
+        }
+
+        [Fact]
+        public void CrossApply_Column_Reusability()
+        {
+            var q = new Query("users").Select("name", "salary", "taxbracket", "taxamount", "grosspay")
+                .CrossApply(new Query().SelectRaw("case when salary < 5000 then 10 when salary < 10000 then 20 else 30 end as taxbracket").As("t1"), j => j)
+                .CrossApply(new Query().SelectRaw("salary * taxbracket as taxamount").As("t2"), j => j)
+                .CrossApply(new Query().SelectRaw("salary - taxamount as grosspay").As("t3"), j => j);
+            var c = Compilers.CompileFor(EngineCodes.SqlServer, q);
+
+            Assert.Equal(string.Join("\n", new[] {
+                "SELECT [name], [salary], [taxbracket], [taxamount], [grosspay] FROM [users] ",
+                "CROSS APPLY (SELECT case when salary < 5000 then 10 when salary < 10000 then 20 else 30 end as taxbracket) AS [t1]",
+                "CROSS APPLY (SELECT salary * taxbracket as taxamount) AS [t2]",
+                "CROSS APPLY (SELECT salary - taxamount as grosspay) AS [t3]",
+            }), c.ToString());
+        }
     }
 }

QueryBuilder/Compilers/Compiler.cs

@@ -647,14 +647,14 @@ public virtual string CompileTableExpression(SqlResult ctx, AbstractFrom from)
 
         public virtual string CompileFrom(SqlResult ctx)
         {
-            if (!ctx.Query.HasComponent("from", EngineCode))
+            if (ctx.Query.HasComponent("from", EngineCode))
             {
-                throw new InvalidOperationException("No table is set");
-            }
+                var from = ctx.Query.GetOneComponent<AbstractFrom>("from", EngineCode);
 
-            var from = ctx.Query.GetOneComponent<AbstractFrom>("from", EngineCode);
+                return "FROM " + CompileTableExpression(ctx, from);
+            }
 
-            return "FROM " + CompileTableExpression(ctx, from);
+            return string.Empty;
         }
 
         public virtual string CompileJoins(SqlResult ctx)

QueryBuilder/Query.Join.cs

@@ -71,5 +71,45 @@ public Query CrossJoin(string table)
             return Join(j => j.JoinWith(table).AsCross());
         }
 
+        public Query CrossApply(string table, string first, string second, string op = "=")
+        {
+            return Join(table, first, second, op, "cross apply");
+        }
+
+        public Query CrossApply(string table, Func<Join, Join> callback)
+        {
+            return Join(table, callback, "cross apply");
+        }
+
+        public Query CrossApply(Query query, Func<Join, Join> onCallback)
+        {
+            return Join(query, onCallback, "cross apply");
+        }
+
+        public Query CrossApply(Query query)
+        {
+            return Join(query, j => j, "cross apply");
+        }
+
+        public Query OuterApply(string table, string first, string second, string op = "=")
+        {
+            return Join(table, first, second, op, "outer apply");
+        }
+
+        public Query OuterApply(string table, Func<Join, Join> callback)
+        {
+            return Join(table, callback, "outer apply");
+        }
+
+        public Query OuterApply(Query query, Func<Join, Join> onCallback)
+        {
+            return Join(query, onCallback, "outer apply");
+        }
+
+        public Query OuterApply(Query query)
+        {
+            return Join(query, j => j, "outer apply");
+        }
+
     }
 }