Question

以下查询将导致“检查每个记录的范围（索引映射：0x7）”。我期望，因为有一个lft + rght索引，它将使用此索引。我已经在文章Mysql range check instead of index usage on inner join上找到了，但是此表使用了自己的结构，因此列类型完全相同。我使用的是MySQL 5.7。

DROP TABLE IF EXISTS test.tree;
CREATE TABLE test.tree (
    lft INT(10) UNSIGNED NOT NULL,
    rght INT(10) UNSIGNED NOT NULL,
    INDEX ix_left_right (lft, rght),
    INDEX ix_left (lft),
    INDEX ix_right (rght)
);

EXPLAIN
SELECT X.*
FROM test.tree X
LEFT JOIN test.tree Y ON  X.lft BETWEEN Y.lft AND Y.rght;

结果

{
    "table": "UnknownTable",
    "rows":
    [
        {
            "id": 1,
            "select_type": "SIMPLE",
            "table": "X",
            "partitions": null,
            "type": "index",
            "possible_keys": null,
            "key": "ix_left_right",
            "key_len": "8",
            "ref": null,
            "rows": 1,
            "filtered": 100.00,
            "Extra": "Using index"
        },
        {
            "id": 1,
            "select_type": "SIMPLE",
            "table": "Y",
            "partitions": null,
            "type": "ALL",
            "possible_keys": "ix_left_right,ix_left,ix_right",
            "key": null,
            "key_len": null,
            "ref": null,
            "rows": 1,
            "filtered": 100.00,
            "Extra": "Range checked for each record (index map: 0x7)"
        }
    ]
}

有人知道我在做什么吗？

MySQL-JOIN BETWEEN-检查每个记录的范围（索引图：0x7）

0 个答案: