In terms of SQL, function means, definitely it returns result. Where as in the WHERE clause we use relational operators (>, <, =, LE, GE) etc. In the where clause, we may or may not get the result.
If we want to find a certain character position in a String, we use INSTR function. Look at the syntax.
Syntax for INSTR()
INSTR(Colname, character to which position we need,start position,which char you need)
“Rani Raghav” – I want to find position for first space.
Select INSTR(name, ' ', 1, 1) from emp;
The result will be – 5.