One question from ISTQB security exam, how to test SQL injection efficiently?

Question

If we are to use equivalent partitioning technique, which one of the following answers is the most efficient to test against SQL injection?

1. bbbbb,12345,'
2. %, ', @, abn123
3. ', ab123
4. '

Answer 1

The answer is 3.

bbbbb,12345,'

This answer is correct, but from equivalent partitioning point of view, it offers two valid inputs, bbbbb and 12345, from valid input partitioning.

%, ', @, abn123

This answer has three valid inputs from valid input partitioning.

', 123

This answer has one valid input and one escape character.

'

This answer has only got one escape character, no valid input at all.

Please bear in mind, ISTQB exam does not cover everything, letting alone SQL injection techniques. I suggest you spend some time studying SQL injection, there is a good link here. SQL Injection OWASP