使用正則表達式在字符串中最后一次出現之后獲取

Question

我有一個SQL字符串，我需要從主“ FROM”值中獲取表名。 我需要找到最后一個“ FROM”出現，其后可能有也可能沒有其他約束。 字符串顯示的幾種方法如下：

$input = "SELECT title, (SELECT name FROM Contact WHERE name = 'foo') as name FROM Account WHERE title = 'president'";
$input = "SELECT title, (SELECT name FROM Contact WHERE name = 'foo') as name FROM Account LIMIT 1";
$input = "SELECT title, (SELECT name FROM Contact WHERE name = 'foo') as name FROM Account OFFSET 3";
$input = "SELECT title, (SELECT name FROM Contact WHERE name = 'foo') as name FROM Account ANYTHING_HERE_REALLY";
$input = "SELECT title, (SELECT name FROM Contact WHERE name = 'foo') as name FROM Account";

所有人的預期輸出為： 帳戶

從搜尋論壇中的任何活動開始，這就是我要走的方向，但是我知道這是不正確的。

preg_match('/.*FROM\s([^]]+)\sWHERE/', $input, $output);

Answer 1

首先，將正則表達式用於級聯內容（如級聯查詢）是一種不好的做法。 但是我們開始...

只需匹配FROM之后的非空格序列。

注意：由於.*的Kleene星的貪婪 ，它肯定會尋找最新的比賽。 您的模式實際上旨在通過期望WHERE子句來過度說明問題。

preg_match('/.*FROM\s+(\S+)/', $input, $output);

示例 （帶有給定的示例和交互式php -a ）：

$ php -a
php > $input = "SELECT title, (SELECT name FROM Contact WHERE name = 'foo') as name FROM Account WHERE title = 'president'";
php > preg_match('/.*FROM\s+(\S+)/', $input, $output);var_dump($output);
array(2) {
  [0]=>
  string(80) "SELECT title, (SELECT name FROM Contact WHERE name = 'foo') as name FROM Account"
  [1]=>
  string(7) "Account"
}
php > $input = "SELECT title, (SELECT name FROM Contact WHERE name = 'foo') as name FROM Account LIMIT 1";
php > preg_match('/.*FROM\s+(\S+)/', $input, $output);var_dump($output);
array(2) {
  [0]=>
  string(80) "SELECT title, (SELECT name FROM Contact WHERE name = 'foo') as name FROM Account"
  [1]=>
  string(7) "Account"
}
php > $input = "SELECT title, (SELECT name FROM Contact WHERE name = 'foo') as name FROM Account OFFSET 3";
php > preg_match('/.*FROM\s+(\S+)/', $input, $output);var_dump($output);
array(2) {
  [0]=>
  string(80) "SELECT title, (SELECT name FROM Contact WHERE name = 'foo') as name FROM Account"
  [1]=>
  string(7) "Account"
}
php > $input = "SELECT title, (SELECT name FROM Contact WHERE name = 'foo') as name FROM Account ANYTHING_HERE_REALLY";
php > preg_match('/.*FROM\s+(\S+)/', $input, $output);var_dump($output);
array(2) {
  [0]=>
  string(80) "SELECT title, (SELECT name FROM Contact WHERE name = 'foo') as name FROM Account"
  [1]=>
  string(7) "Account"
}
php > $input = "SELECT title, (SELECT name FROM Contact WHERE name = 'foo') as name FROM Account";
php > preg_match('/.*FROM\s+(\S+)/', $input, $output);var_dump($output);
array(2) {
  [0]=>
  string(80) "SELECT title, (SELECT name FROM Contact WHERE name = 'foo') as name FROM Account"
  [1]=>
  string(7) "Account"
}

Answer 2

這應該為您工作：

preg_match_all('/FROM\s?(\S+)/', $input, $output);

$輸出：

Array
(
    [0] => Array
        (
            [0] => FROM Contact
            [1] => FROM Account
        )

    [1] => Array
        (
            [0] => Contact
            [1] => Account
        )

)