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SELECT 
  * 
FROM 
  cscart_vd_vendors_relationships 
WHERE 
  brand_id = 123

Query time 0.00043

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_vd_vendors_relationships",
          "access_type": "ref",
          "possible_keys": ["brand_id"],
          "key": "brand_id",
          "key_length": "4",
          "used_key_parts": ["brand_id"],
          "ref": ["const"],
          "rows": 21,
          "filtered": 100
        }
      }
    ]
  }
}

Result

id	brand_id	feature_id	variant_id	lang_code
11986	123	661	2198	es
11985	123	649	1925	es
11984	123	648	1920	es
11983	123	654	2140	es
11982	123	647	1890	es
11981	123	662	2211	es
11980	123	662	2202	es
11979	123	660	2188	es
11978	123	658	2186	es
11977	123	652	2108	es
11976	123	652	2107	es
11975	123	652	2117	es
11974	123	652	2124	es
11973	123	652	2115	es
11972	123	652	2114	es
11971	123	652	2116	es
11970	123	646	1887	es
11969	123	653	2129	es
11968	123	653	2128	es