MySQL 8.0

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CREATE TABLE examples (
  col_value VARCHAR(255)
);

INSERT INTO examples VALUES
  ('10090'),
  ('10000'),
  ('100§0'),
  ('10120012');
SELECT col_value,
  (LENGTH(col_value) - LENGTH(REPLACE(col_value, '0', ''))) AS char_count
FROM examples


col_value
char_count


10090
3

10000
4

100§0
3

10120012
3


-- count string values using multiple characters.
SELECT col_value,
  FLOOR((CHAR_LENGTH(col_value) - CHAR_LENGTH(REPLACE(col_value, '12', ''))) / CHAR_LENGTH('12')) AS char_count
FROM examples;


col_value
char_count


10090
0

10000
0

100§0
0

10120012
2


-- use this solution (using CHAR_LENGTH) to count multi-byte characters.
SELECT col_value,
  (CHAR_LENGTH(col_value) - CHAR_LENGTH(REPLACE(col_value, '§', ''))) AS char_count
FROM examples;

-- don't use this solution (using LENGTH) to count multi-byte characters.
SELECT col_value,
  (LENGTH(col_value) - LENGTH(REPLACE(col_value, '§', ''))) AS char_count
FROM examples;


col_value
char_count


10090
0

10000
0

100§0
1

10120012
0




col_value
char_count


10090
0

10000
0

100§0
2

10120012
0


-- count a string value using multiple characters.
SELECT col_value,
  FLOOR((CHAR_LENGTH(col_value) - CHAR_LENGTH(REPLACE(col_value, '12', ''))) / CHAR_LENGTH('12')) AS str_count
FROM examples;


col_value
str_count


10090
0

10000
0

100§0
0

10120012
2