Restore SqlFragment fluent chain, inline concatenation was slower

The array+implode approach in SqlFragment calculates total length and
does one allocation. Repeated string .= copies the growing string each
iteration — measurably slower on the complex select benchmark
(19μs → 28μs regression). Restore the fluent chain while keeping
the Quantifier simplification and Table::prepare direct field access.

Signed-off-by: Simon Mundy <simon.mundy@peptolab.com>

Author: simon-mundy

src/Sql/Delete.php

@@ -8,6 +8,7 @@
 use PhpDb\Adapter\Driver\DriverInterface;
 use PhpDb\Adapter\ParameterContainer;
 use PhpDb\Adapter\Platform\PlatformInterface;
+use PhpDb\Sql\Part\SqlFragment;
 use PhpDb\Sql\Part\SqlProcessor;
 use PhpDb\Sql\Part\From;
 use PhpDb\Sql\Part\Where as WherePart;
@@ -89,15 +90,9 @@ public function buildSqlString(
         $processor->setParamPrefix($this->processInfo['paramPrefix']);
         $sqlPlatform?->getTypeDecorator($this)?->prepare($this, $processor);
 
-        $sql = $this->getStatementKeyword();
-        if (($part = $this->table->toSql($processor)) !== null) {
-            $sql .= ' ' . $part;
-        }
-        if (($part = $this->where?->toSql($processor)) !== null) {
-            $sql .= ' ' . $part;
-        }
-
-        return $sql;
+        return (string) SqlFragment::of($this->getStatementKeyword())
+            ->part($this->table->toSql($processor))
+            ->part($this->where?->toSql($processor));
     }
 
     /**

src/Sql/Part/SqlFragment.php

@@ -0,0 +1,40 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PhpDb\Sql\Part;
+
+use function implode;
+
+final class SqlFragment
+{
+    private array $parts = [];
+
+    public static function of(string $keyword): self
+    {
+        $f = new self();
+        $f->parts[] = $keyword;
+        return $f;
+    }
+
+    public function part(?string $part): self
+    {
+        if ($part !== null) {
+            $this->parts[] = $part;
+        }
+        return $this;
+    }
+
+    public function wrap(?string $suffix): self
+    {
+        if ($suffix !== null) {
+            $this->parts = ['( ' . implode(' ', $this->parts) . ' )', $suffix];
+        }
+        return $this;
+    }
+
+    public function __toString(): string
+    {
+        return implode(' ', $this->parts);
+    }
+}

src/Sql/Select.php

@@ -15,6 +15,7 @@
 use PhpDb\Sql\Part\Offset;
 use PhpDb\Sql\Part\OrderBy;
 use PhpDb\Sql\Part\Quantifier;
+use PhpDb\Sql\Part\SqlFragment;
 use PhpDb\Sql\Part\SqlProcessor;
 use PhpDb\Sql\Part\Table;
 use PhpDb\Sql\Part\Where as WherePart;
@@ -386,41 +387,18 @@ public function buildSqlString(
         $sqlPlatform?->getTypeDecorator($this)?->prepare($this, $processor);
         $this->table->prepare($processor);
 
-        $sql = 'SELECT';
-
-        if (($part = $this->quantifier?->toSql($processor)) !== null) {
-            $sql .= ' ' . $part;
-        }
-        $sql .= ' ' . $this->table->columns()->toSql($processor);
-        if (($part = $this->table->from()->toSql($processor)) !== null) {
-            $sql .= ' ' . $part;
-        }
-        if (($part = $this->table->joins()?->toSql($processor)) !== null) {
-            $sql .= ' ' . $part;
-        }
-        if (($part = $this->where?->toSql($processor)) !== null) {
-            $sql .= ' ' . $part;
-        }
-        if (($part = $this->groupBy?->toSql($processor)) !== null) {
-            $sql .= ' ' . $part;
-        }
-        if (($part = $this->having?->toSql($processor)) !== null) {
-            $sql .= ' ' . $part;
-        }
-        if (($part = $this->orderBy?->toSql($processor)) !== null) {
-            $sql .= ' ' . $part;
-        }
-        if (($part = $this->limit?->toSql($processor)) !== null) {
-            $sql .= ' ' . $part;
-        }
-        if (($part = $this->offset?->toSql($processor)) !== null) {
-            $sql .= ' ' . $part;
-        }
-        if (($part = $this->combine?->toSql($processor)) !== null) {
-            $sql = '( ' . $sql . ' ) ' . $part;
-        }
-
-        return $sql;
+        return (string) SqlFragment::of('SELECT')
+            ->part($this->quantifier?->toSql($processor))
+            ->part($this->table->columns()->toSql($processor))
+            ->part($this->table->from()->toSql($processor))
+            ->part($this->table->joins()?->toSql($processor))
+            ->part($this->where?->toSql($processor))
+            ->part($this->groupBy?->toSql($processor))
+            ->part($this->having?->toSql($processor))
+            ->part($this->orderBy?->toSql($processor))
+            ->part($this->limit?->toSql($processor))
+            ->part($this->offset?->toSql($processor))
+            ->wrap($this->combine?->toSql($processor));
     }
 
     /**

src/Sql/Update.php

@@ -10,6 +10,7 @@
 use PhpDb\Adapter\Platform\PlatformInterface;
 use PhpDb\Sql\Part\Joins as JoinsPart;
 use PhpDb\Sql\Part\Set as SetPart;
+use PhpDb\Sql\Part\SqlFragment;
 use PhpDb\Sql\Part\SqlProcessor;
 use PhpDb\Sql\Part\From;
 use PhpDb\Sql\Part\Where as WherePart;
@@ -135,19 +136,11 @@ public function buildSqlString(
         $processor->setParamPrefix($this->processInfo['paramPrefix']);
         $sqlPlatform?->getTypeDecorator($this)?->prepare($this, $processor);
 
-        $sql = $this->getStatementKeyword();
-        $sql .= ' ' . $this->table->renderTable($processor);
-        if (($part = $this->joins?->toSql($processor)) !== null) {
-            $sql .= ' ' . $part;
-        }
-        if (($part = $this->set->toSql($processor)) !== null) {
-            $sql .= ' ' . $part;
-        }
-        if (($part = $this->where?->toSql($processor)) !== null) {
-            $sql .= ' ' . $part;
-        }
-
-        return $sql;
+        return (string) SqlFragment::of($this->getStatementKeyword())
+            ->part($this->table->renderTable($processor))
+            ->part($this->joins?->toSql($processor))
+            ->part($this->set->toSql($processor))
+            ->part($this->where?->toSql($processor));
     }
 
     /**