system/Database/Forge.php
protected function _processPrimaryKeys(string $table): string
	{
		$sql = '';

		for ($i = 0, $c = count($this->primaryKeys); $i < $c; $i++)
		{
			if (! isset($this->fields[$this->primaryKeys[$i]]))
			{
				unset($this->primaryKeys[$i]);
			}
		}

		if (count($this->primaryKeys) > 0)
		{
			$sql .= ",\n\tCONSTRAINT " . $this->db->escapeIdentifiers('pk_' . $table)
					. ' PRIMARY KEY(' . implode(', ', $this->db->escapeIdentifiers($this->primaryKeys)) . ')';
		}

		return $sql;
	}
protected function _processPrimaryKeys(string $table): string
	{
		$sql = '';

		for ($i = 0, $c = count($this->primaryKeys); $i < $c; $i++)
		{
			if (! isset($this->fields[$this->primaryKeys[$i]]))
			{
				unset($this->primaryKeys[$i]);
			}
		}

		if (count($this->primaryKeys) > 0)
		{
			$sql .= ",\n\tCONSTRAINT " . $this->db->escapeIdentifiers('pk_' . $table)
					. ' PRIMARY KEY(' . implode(', ', $this->db->escapeIdentifiers($this->primaryKeys)) . ')';
		}

		return $sql;
	}
Process primary keys

@param string $table Table name

@return string