Oracle 11g Release 2

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CREATE FUNCTION GetStringCount(strValue NVARCHAR2, strChar NVARCHAR2)
RETURN NUMBER DETERMINISTIC IS
BEGIN
  RETURN COALESCE((LENGTH(strValue) - 
    LENGTH(REPLACE(strValue, strChar, ''))) / 
    LENGTH(strChar), 0);
END;
/
CREATE TABLE example (
  col NVARCHAR2(2000)
);
INSERT INTO example (col) VALUES ('Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua.');
1 rows affected

INSERT INTO example (col) VALUES ('At vero eos et accusam et justo duo dolores et ea rebum.');
1 rows affected

INSERT INTO example (col) VALUES ('Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet.');
1 rows affected

INSERT INTO example (col) VALUES (NULL);
1 rows affected

SELECT GetStringCount('Hello', 'l') FROM dual;

GETSTRINGCOUNT('HELLO','L')

2

SELECT GetStringCount('This costs 5$.', '$') FROM dual;

GETSTRINGCOUNT('THISCOSTS5$.','$')

1

SELECT GetStringCount('This costs 5€.', '€') FROM dual;

GETSTRINGCOUNT('THISCOSTS5€.','€')

1

SELECT col, GetStringCount(col, 'a') FROM example;

COL
GETSTRINGCOUNT(COL,'A')

Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua.
11

At vero eos et accusam et justo duo dolores et ea rebum.
3

Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet.
8

null
0

COL	GETSTRINGCOUNT(COL,'A')
Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua.	11
At vero eos et accusam et justo duo dolores et ea rebum.	3
Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet.	8
null	0