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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '6188e081d4a5224c2965e65ef18f13138de1cc8512e12213efcb581626a72404' 
  AND token = '2YmQij2MTYX5facTRnhMXF23LkugpRGYLBpG4IcCxwY=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00030

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}