Avoid building a field multiple times if clause has synonyms.

Author: udan11

src/Statement.php

@@ -108,6 +108,20 @@ public function build()
          */
         $query = '';
 
+        /**
+         * Clauses which were built already.
+         *
+         * It is required to keep track of built clauses because some fields,
+         * for example `join` is used by multiple clauses (`JOIN`, `LEFT JOIN`,
+         * `LEFT OUTER JOIN`, etc.). The same happens for `VALUE` and `VALUES`.
+         *
+         * A clause is considered built just after fields' value
+         * (`$this->field`) was used in building.
+         *
+         * @var array
+         */
+        $built = array();
+
         foreach (static::$CLAUSES as $clause) {
             /**
              * The name of the clause.
@@ -144,6 +158,15 @@ public function build()
                 continue;
             }
 
+            // Checking if this field was already built.
+            if ($type & 1) {
+                if (!empty($built[$field])) {
+                    continue;
+                }
+
+                $built[$field] = true;
+            }
+
             // Checking if the name of the clause should be added.
             if ($type & 2) {
                 $query .= $name . ' ';

tests/Builder/SelectStatementTest.php

@@ -0,0 +1,26 @@
+<?php
+
+namespace SqlParser\Tests\Builder;
+
+use SqlParser\Parser;
+
+use SqlParser\Tests\TestCase;
+
+class SelectStatementTest extends TestCase
+{
+
+    public function testBuilder()
+    {
+        $query = 'SELECT * FROM t1 LEFT JOIN (t2, t3, t4) '
+            . 'ON (t2.a=t1.a AND t3.b=t1.b AND t4.c=t1.c)';
+
+        $parser = new Parser($query);
+        $stmt = $parser->statements[0];
+
+        $this->assertEquals(
+            'SELECT  * FROM t1 LEFT JOIN (t2, t3, t4) '
+            . 'ON (t2.a=t1.a AND t3.b=t1.b AND t4.c=t1.c) ',
+            $stmt->build()
+        );
+    }
+}