$re = '/\s([A-Z_]+\.)([A-Za-z0-9_]+)/';
$str = 'SELECT HOSP.TIPO, HOSP.FECHA_INGRESO, HOSP.FECHA_ALTA, HOSP.NHC, HOSP.EPISODIO, HOSP.ID, HOSP.SEXO, HOSP.FNAC, HOSP.MEDICO, HOSP.MUTUA, HOSP.MOTIVO, HOSP.DIAG, HOSP.PROC, HOSP.MES_ALTA, HOSP.ESPECIALIDAD, HOSP.ESTADO
FROM HOSP;
';
$subst = " MAX(Len(\1\2)) AS \2";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php