SELECT 
  gallery_id, 
  placeholder 
FROM 
  cscart_cp_image_galleries 
WHERE 
  status = 'A' 
  AND dependent != 'Y' 
  AND placeholder != ""

Query time 0.00022

JSON explain

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