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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '21a37a5f7752bbc3f70a89644e08122f3daa0bb511a0db49ad2a7746141bf8bd' 
  AND token = 'QvXmIQcqXkblCfBzSR5cMMuSFYrdmC0aCi/mhL+c5Oc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00046

JSON explain

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