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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b3a99fa183ff161c75617f8d9181ef3a5ea4d383ab3bc0d787ee43d1e1d5ad6e' 
  AND token = '6xuxC7UwsTyDoLZWUQ+bZ3mZU6ubmwMzesqkqUZhsBo=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00020

JSON explain

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