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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '6df9704224b3567167dd3a17c4c8a39fac99923b0321969fa770c34d0992b71d' 
  AND token = '/QoR/QmeALJX7YYpo9CfUH3bG+jb87khduLs3iCy8bo=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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