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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b8fb5996ad635d66c8d3ed85cfbecc69a19a19dab29529bcf78a6473a0c6dd5c' 
  AND token = 'Xp68AXimpb1aA4IxyHKNxTm8XlSWgEsCzdF2ya2QyyE=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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