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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '6f796ee8178972161a287b96928923727dddf9094643b9e482f0218498fddd5b' 
  AND token = '5oF0LyfymojxAhBpNPQayGLa2U9bfFMPCO7JK7MsccI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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