SELECT 
  tag_id 
FROM 
  cscart_tags 
WHERE 
  tag = 'Видеонаблюдение'

Query time 0.00041

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "1.20"
    },
    "table": {
      "table_name": "cscart_tags",
      "access_type": "ref",
      "possible_keys": [
        "tag"
      ],
      "key": "tag",
      "used_key_parts": [
        "tag"
      ],
      "key_length": "767",
      "ref": [
        "const"
      ],
      "rows_examined_per_scan": 1,
      "rows_produced_per_join": 1,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "1.00",
        "eval_cost": "0.20",
        "prefix_cost": "1.20",
        "data_read_per_join": "800"
      },
      "used_columns": [
        "tag_id",
        "tag"
      ]
    }
  }
}