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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51c0b2a3fec27b00822f28c49b69b8399dec58653b397dc66046b6328e1005b2' 
  AND token = '5ZsbCmU5iMGmFYdwMs1z1s3vfanGsh1IRT+TBk4CG+k=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00037

JSON explain

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