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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'c76acdccc4c2e80eb8a9543c7ac1e79fe2b1f17cc5e1ec4d6a55375ee804cb50' 
  AND token = 'OpzHchZlsck+XT3Cw26Hhv8bF2av0BMNarqdsshSaLs=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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