sql expression (lots of todo)

core/Driver/SQL/Expression/CurrentTimeStamp.class.php

@@ -0,0 +1,7 @@
+<?php
+
+namespace Driver\SQL\Expression;
+
+class CurrentTimeStamp extends Expression {
+
+}

core/Driver/SQL/Expression/DateAdd.class.php

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+<?php
+
+namespace Driver\SQL\Expression;
+
+use Driver\SQL\SQL;
+
+class DateAdd extends Expression {
+
+  private Expression $lhs;
+  private Expression $rhs;
+  private string $unit;
+
+  public function __construct(Expression $lhs, Expression $rhs, string $unit) {
+    $this->lhs = $lhs;
+    $this->rhs = $rhs;
+    $this->unit = $unit;
+  }
+
+  public function getLHS(): Expression { return $this->lhs; }
+  public function getRHS(): Expression { return $this->rhs; }
+  public function getUnit(): string { return $this->unit; }
+
+}

core/Driver/SQL/Expression/Expression.class.php

@@ -0,0 +1,9 @@
+<?php
+
+namespace Driver\SQL\Expression;
+
+use Driver\SQL\SQL;
+
+abstract class Expression {
+
+}