In Oracle the INSTR function allows you to find the position of substring in a string. It accepts 2, 3 or 4 parameters.
In Snowflake you have to use the REGEXP_INSTR function that also accepts 2, 3 or 4 parameters.
INSTR with 2 parameters searches the specified substring from the beginning of string:
Oracle:
-- Find substring in string SELECT INSTR('abc', 'b') FROM dual; # 2
Snowflake:
-- Find substring in string SELECT REGEXP_INSTR('abc', 'b'); # 2
INSTR with 3 parameters starts searching the specified substring from the specified position of string:
Oracle:
-- Find substring in string starting from 3 position SELECT INSTR('abcb', 'b', 3) FROM dual; # 4
Snowflake:
-- Find substring in string starting from 3 position SELECT REGEXP_INSTR('abcb', 'b', 3); # 4
INSTR with 4 parameters starts searching the specified substring from the specified position and returns the position of the specified occurrence of string:
Oracle:
-- Find 2nd occurrence of substring in string starting from 3 position SELECT INSTR('abcbcb', 'b', 3, 2) FROM dual; # 6
Snowflake:
-- Find substring in string starting from 3 position SELECT REGEXP_INSTR('abcbcb', 'b', 3, 2); # 6
For more information, see Oracle to Snowflake Migration.