哪个更好使用查询？

Question

我是mysql的新手。

有这样一个计划：

      -- auto-generated definition
  create table category
  (
    id bigint not null auto_increment
      primary key,
    name varchar(255) not null
  )
  ;

  INSERT INTO `category` (`id`, `name`) VALUES (1, 'category1'), (2, 'category2'), (3, 'category3');

    -- auto-generated definition
  create table unit
  (
    id bigint not null auto_increment
      primary key,
    name varchar(128) not null
  )
  ;

  INSERT INTO `unit` (`id`, `name`)
  VALUES
    (1, 'unit1'),
    (2, 'unit2'),
    (3, 'unit3'),
    (4, 'unit4'),
    (5, 'unit5'),
    (6, 'unit6'),
    (7, 'unit7'),
    (8, 'unit8'),
    (9, 'unit9');

  -- auto-generated definition
  create table category_unit
  (
    id bigint not null auto_increment
      primary key,
    category_id bigint not null,
    unit_id bigint not null,
    constraint category_id_2
    unique (category_id, unit_id)
  )
  ;

  create index category_id
    on category_unit (category_id)
  ;

  create index unit_id
    on category_unit (unit_id)
  ;

  INSERT INTO `category_unit` (`category_id`, `unit_id`)
  VALUES
    (1, 2),
    (1, 3),
    (1, 4),
    (2, 4),
    (2, 5),
    (2, 6),
    (3, 7),
    (3, 3);

我创建了3个不同的查询：

1）

EXPLAIN SELECT
      C.id,
      C.name,
      CU.name as units
    FROM
      category C
      LEFT JOIN (
                  SELECT
                    CU.category_id,
                    GROUP_CONCAT(DISTINCT U.name ORDER BY U.name ASC SEPARATOR ', ') AS name
                  FROM category_unit CU
                  LEFT JOIN unit U ON U.id = CU.unit_id
                  GROUP BY CU.category_id
                ) as CU ON CU.category_id = C.id
    WHERE
      (CU.name LIKE "%unit2%" OR C.id LIKE "%unit2%" OR C.name LIKE "%unit2%")
    GROUP BY
      C.id;

这不是很好，因为它会扫描整个表格

2）

EXPLAIN SELECT
      C.id,
      C.name,
      GROUP_CONCAT(DISTINCT U_current.name ORDER BY U_current.name ASC SEPARATOR ', ') AS name
    FROM
      category C
      LEFT JOIN category_unit CU ON CU.category_id = C.id
      LEFT JOIN unit U ON U.id = CU.unit_id
      LEFT JOIN category_unit CU_current ON CU_current.category_id = C.id
      LEFT JOIN unit U_current ON U_current.id = CU_current.unit_id
    WHERE
      (U.name LIKE "%unit2%" OR C.id LIKE "%unit2%" OR C.name LIKE "%unit2%")
    GROUP BY
      C.id;

这样做更好，但您必须再次选择相同的表格以选择所有分组的单位

3）

EXPLAIN SELECT
      C.id,
      C.name,
      GROUP_CONCAT(DISTINCT U.name ORDER BY U.name ASC SEPARATOR ', ') AS name
    FROM
      category C
      LEFT JOIN category_unit CU ON CU.category_id = C.id
      LEFT JOIN unit U ON U.id = CU.unit_id
    WHERE
      C.id IN (
        SELECT
          C.id
        FROM
          category C
          LEFT JOIN category_unit CU ON CU.category_id = C.id
          LEFT JOIN unit U ON U.id = CU.unit_id
        WHERE
          (U.name LIKE "%unit2%" OR C.id LIKE "%unit2%" OR C.name LIKE "%unit2%")
      )
    GROUP BY
      C.id;

在这里你必须进行2次相同的查询

P.S。 “WHERE”自动生成