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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '27c9fac8169ca5ea7d7fbd42c5bd708fad5e68377eda8241c08f41f2ff3f4b21' 
  AND token = 'FUAAfMoRfGwAUEwkPxqLDjkqx54JJBV3qxij8vnMA98=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00039

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE noticed after reading const tables"
    }
  }
}