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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '0e2846921950c15ef35fd49b80db96b0a5bcd898f75fa99de3e1593d2dcab875' 
  AND token = 'BiiPjQaPlzso7ExmLuI+Mx/sM31ql3tUXXPNCETLXD0=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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