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# CHARINDEX

`CHARINDEX` fonksiyonu, bir dizgenin içinde belirli bir karakter dizisinin bulunup bulunmadığını veya bulunması durumunda hangi indekste bulunduğunu belirler.

Kullanım şekli:

```sql
CHARINDEX(expression_to_find, string_expression [, start_location])
```

* `expression_to_find`: aranacak karakter dizgesi
* `string_expression`: analiz edilecek dize
* `start_location`: aramanın başlangıç noktası (opsiyonel)

Eğer aranacak karakter dizgesi bulunamazsa, `CHARINDEX` 0 döndürür.

Örnek olarak:

```sql
DECLARE @name VARCHAR(50) = 'John Doe';

SELECT @name AS original_name,
       CHARINDEX('Doe', @name) AS index_of_substring;
```

Bu örnekte, `'John Doe'` dizesinin içinde `'Doe'` karakter dizgesinin bulunup bulunmadığı kontrol edilir ve `5` indeksi döndürür çünkü `'Doe'` dizesi `'John Doe'` dizesinin beşinci karakterinden başlar.


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