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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'c21752208fb9b4220a08ac49c8537b41c70309caad5d58d240f39f6992b94349' 
  AND token = '7bUrmdGTYCyGCZ068UVBhkYYCvMuNP+7SVz9/Yyizt4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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