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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '76240f21f2f055f14403efb1b07c85693222e624b0800c46ef7e84c2a04d20d0' 
  AND token = 'PRb2uOsDBVOhTumAysaVkyP5TXrqWx35v4tcMWq1bYc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00038

JSON explain

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