Postgresql 9.0+: Better version of IntervalToMilliseconds expression

Based on epoch extraction, it is less complicated than sum of several parts
expecially when base expression is complicated so it required many copies of
base expression.
New approach is also lest costy.

Author: alex-kulakov

Orm/Xtensive.Orm.PostgreSql/Sql.Drivers.PostgreSql/v8_0/Compiler.cs

@@ -122,7 +122,7 @@ public override void Visit(SqlFunctionCall node)
           ((node.Arguments[0] / SqlDml.Literal(nanosecondsPerSecond)) * OneSecondInterval).AcceptVisitor(this);
           return;
         case SqlFunctionType.IntervalToMilliseconds:
-          SqlHelper.IntervalToMilliseconds(node.Arguments[0]).AcceptVisitor(this);
+          VisitIntervalToMilliseconds(node);
           return;
         case SqlFunctionType.IntervalToNanoseconds:
           SqlHelper.IntervalToNanoseconds(node.Arguments[0]).AcceptVisitor(this);
@@ -296,6 +296,11 @@ public override void Visit(SqlCustomFunctionCall node)
       base.Visit(node);
     }
 
+    protected virtual void VisitIntervalToMilliseconds(SqlFunctionCall node)
+    {
+      SqlHelper.IntervalToMilliseconds(node.Arguments[0]).AcceptVisitor(this);
+    }
+
     private static SqlExpression DateTimeToStringIso(SqlExpression dateTime, in string isoFormat) =>
       SqlDml.FunctionCall("TO_CHAR", dateTime, isoFormat);
 

Orm/Xtensive.Orm.PostgreSql/Sql.Drivers.PostgreSql/v9_0/Compiler.cs

@@ -4,11 +4,21 @@
 // Created by: Denis Krjuchkov
 // Created:    2012.06.06
 
+using Xtensive.Sql.Dml;
+
 namespace Xtensive.Sql.Drivers.PostgreSql.v9_0
 {
   internal class Compiler : v8_4.Compiler
   {
     // Constructors
+    protected override void VisitIntervalToMilliseconds(SqlFunctionCall node)
+    {
+      AppendSpaceIfNecessary();
+      _ = context.Output.Append("(EXTRACT(EPOCH FROM (");
+      node.Arguments[0].AcceptVisitor(this);
+      _ = context.Output.Append(")) * 1000)");
+
+    }
 
     public Compiler(SqlDriver driver)
       : base(driver)