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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'c636d75cabb0c58e213f44ac7644fc7f639254a1747ebc0a9da4eb37044c1421' 
  AND token = '1EuxhH+/105DZa85lnflbe1tXNKBgRTCAxrgic4vMo8=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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