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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '6f6e2c824bf19b56ffbd0844d6edeb0c9e4d432e683d70f031e18e60a3c5ff4a' 
  AND token = '1lVuL5VhyOp7245NiyzWQGFd7aRd7UB08FQDSBZ/5rQ=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00054

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE noticed after reading const tables"
    }
  }
}