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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'c3b90dfc7243655f21f2d90a20f82e7a93fd0608b06ff3896d3471e12fedfc34' 
  AND token = 'UCp63ksiFVSQ0e6+Kd4amvHm7sS6b4D1ySZ4Z33kRQc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00020

JSON explain

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