MySQL explain詳解
Explain簡介
本文主要講述如何經過 explain 命令獲取 select 語句的執行計劃，經過 explain 咱們能夠知道如下信息：表的讀取順序，數據讀取操做的類型，哪些索引可使用，哪些索引實際使用了，表之間的引用，每張表有多少行被優化器查詢等信息。html
下面是使用 explain 的例子： mysql
在 select 語句以前增長 explain 關鍵字，MySQL 會在查詢上設置一個標記，執行查詢時，會返回執行計劃的信息，而不是執行這條SQL（若是 from 中包含子查詢，仍會執行該子查詢，將結果放入臨時表中）。sql
mysql> explain select * from actor; +----+-------------+-------+------+---------------+------+---------+------+------+-------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------+---------+------+------+-------+ | 1 | SIMPLE | actor | ALL | NULL | NULL | NULL | NULL | 2 | NULL | +----+-------------+-------+------+---------------+------+---------+------+------+-------+
在查詢中的每一個表會輸出一行，若是有兩個表經過 join 鏈接查詢，那麼會輸出兩行。表的意義至關普遍：能夠是子查詢、一個 union 結果等。服務器
explain 有兩個變種：性能
1）explain extended：會在 explain 的基礎上額外提供一些查詢優化的信息。緊隨其後經過 show warnings 命令能夠 獲得優化後的查詢語句，從而看出優化器優化了什麼。額外還有 filtered 列，是一個半分比的值，rows * filtered/100 能夠估算出將要和 explain 中前一個表進行鏈接的行數（前一個表指 explain 中的id值比當前表id值小的表）。優化
mysql> explain extended select * from film where id = 1; +----+-------------+-------+-------+---------------+---------+---------+-------+------+----------+-------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+-------+---------------+---------+---------+-------+------+----------+-------+ | 1 | SIMPLE | film | const | PRIMARY | PRIMARY | 4 | const | 1 | 100.00 | NULL | +----+-------------+-------+-------+---------------+---------+---------+-------+------+----------+-------+ mysql> show warnings; +-------+------+--------------------------------------------------------------------------------+ | Level | Code | Message | +-------+------+--------------------------------------------------------------------------------+ | Note | 1003 | /* select#1 */ select '1' AS `id`,'film1' AS `name` from `test`.`film` where 1 | +-------+------+--------------------------------------------------------------------------------+
2）explain partitions：相比 explain 多了個 partitions 字段，若是查詢是基於分區表的話，會顯示查詢將訪問的分區。spa
explain 中的列
接下來咱們將展現 explain 中每一個列的信息。指針
1. id列
id列的編號是 select 的序列號，有幾個 select 就有幾個id，而且id的順序是按 select 出現的順序增加的。MySQL將 select 查詢分爲簡單查詢和複雜查詢。複雜查詢分爲三類：簡單子查詢、派生表（from語句中的子查詢）、union 查詢。code
1）簡單子查詢htm
mysql> explain select (select 1 from actor limit 1) from film; +----+-------------+-------+-------+---------------+----------+---------+------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+-------+---------------+----------+---------+------+------+-------------+ | 1 | PRIMARY | film | index | NULL | idx_name | 32 | NULL | 1 | Using index | | 2 | SUBQUERY | actor | index | NULL | PRIMARY | 4 | NULL | 2 | Using index | +----+-------------+-------+-------+---------------+----------+---------+------+------+-------------+
2）from子句中的子查詢
mysql> explain select id from (select id from film) as der; +----+-------------+------------+-------+---------------+----------+---------+------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+------------+-------+---------------+----------+---------+------+------+-------------+ | 1 | PRIMARY | <derived2> | ALL | NULL | NULL | NULL | NULL | 2 | NULL | | 2 | DERIVED | film | index | NULL | idx_name | 32 | NULL | 1 | Using index | +----+-------------+------------+-------+---------------+----------+---------+------+------+-------------+
這個查詢執行時有個臨時表別名爲der，外部 select 查詢引用了這個臨時表
3）union查詢
mysql> explain select 1 union all select 1; +----+--------------+------------+------+---------------+------+---------+------+------+-----------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+--------------+------------+------+---------------+------+---------+------+------+-----------------+ | 1 | PRIMARY | NULL | NULL | NULL | NULL | NULL | NULL | NULL | No tables used | | 2 | UNION | NULL | NULL | NULL | NULL | NULL | NULL | NULL | No tables used | | NULL | UNION RESULT | <union1,2> | ALL | NULL | NULL | NULL | NULL | NULL | Using temporary | +----+--------------+------------+------+---------------+------+---------+------+------+-----------------+
union結果老是放在一個匿名臨時表中，臨時表不在SQL總出現，所以它的id是NULL。
2. select_type列
select_type 表示對應行是是簡單仍是複雜的查詢，若是是複雜的查詢，又是上述三種複雜查詢中的哪種。
1）simple：簡單查詢。查詢不包含子查詢和union
mysql> explain select * from film where id = 2; +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------+ | 1 | SIMPLE | film | const | PRIMARY | PRIMARY | 4 | const | 1 | NULL | +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------+
2）primary：複雜查詢中最外層的 select
3）subquery：包含在 select 中的子查詢（不在 from 子句中）
4）derived：包含在 from 子句中的子查詢。MySQL會將結果存放在一個臨時表中，也稱爲派生表（derived的英文含義）
用這個例子來了解 primary、subquery 和 derived 類型
mysql> explain select (select 1 from actor where id = 1) from (select * from film where id = 1) der; +----+-------------+------------+--------+---------------+---------+---------+-------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+------------+--------+---------------+---------+---------+-------+------+-------------+ | 1 | PRIMARY | <derived3> | system | NULL | NULL | NULL | NULL | 1 | NULL | | 3 | DERIVED | film | const | PRIMARY | PRIMARY | 4 | const | 1 | NULL | | 2 | SUBQUERY | actor | const | PRIMARY | PRIMARY | 4 | const | 1 | Using index | +----+-------------+------------+--------+---------------+---------+---------+-------+------+-------------+
5）union：在 union 中的第二個和隨後的 select
6）union result：從 union 臨時表檢索結果的 select
用這個例子來了解 union 和 union result 類型：
mysql> explain select 1 union all select 1; +----+--------------+------------+------+---------------+------+---------+------+------+-----------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+--------------+------------+------+---------------+------+---------+------+------+-----------------+ | 1 | PRIMARY | NULL | NULL | NULL | NULL | NULL | NULL | NULL | No tables used | | 2 | UNION | NULL | NULL | NULL | NULL | NULL | NULL | NULL | No tables used | | NULL | UNION RESULT | <union1,2> | ALL | NULL | NULL | NULL | NULL | NULL | Using temporary | +----+--------------+------------+------+---------------+------+---------+------+------+-----------------+
3. table列
這一列表示 explain 的一行正在訪問哪一個表。
當 from 子句中有子查詢時，table列是 <derivenN> 格式，表示當前查詢依賴 id=N 的查詢，因而先執行 id=N 的查詢。當有 union 時，UNION RESULT 的 table 列的值爲 <union1,2>，1和2表示參與 union 的 select 行id。
4. type列
這一列表示關聯類型或訪問類型，即MySQL決定如何查找表中的行。
依次從最優到最差分別爲：system > const > eq_ref > ref > fulltext > ref_or_null > index_merge > unique_subquery > index_subquery > range > index > ALL
NULL：mysql可以在優化階段分解查詢語句，在執行階段用不着再訪問表或索引。例如：在索引列中選取最小值，能夠單獨查找索引來完成，不須要在執行時訪問表
mysql> explain select min(id) from film; +----+-------------+-------+------+---------------+------+---------+------+------+------------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------+---------+------+------+------------------------------+ | 1 | SIMPLE | NULL | NULL | NULL | NULL | NULL | NULL | NULL | Select tables optimized away | +----+-------------+-------+------+---------------+------+---------+------+------+------------------------------+
const, system：mysql能對查詢的某部分進行優化並將其轉化成一個常量（能夠看show warnings 的結果）。用於 primary key 或 unique key 的全部列與常數比較時，因此表最多有一個匹配行，讀取1次，速度比較快。
mysql> explain extended select * from (select * from film where id = 1) tmp; +----+-------------+------------+--------+---------------+---------+---------+-------+------+----------+-------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+------------+--------+---------------+---------+---------+-------+------+----------+-------+ | 1 | PRIMARY | <derived2> | system | NULL | NULL | NULL | NULL | 1 | 100.00 | NULL | | 2 | DERIVED | film | const | PRIMARY | PRIMARY | 4 | const | 1 | 100.00 | NULL | +----+-------------+------------+--------+---------------+---------+---------+-------+------+----------+-------+ mysql> show warnings; +-------+------+---------------------------------------------------------------+ | Level | Code | Message | +-------+------+---------------------------------------------------------------+ | Note | 1003 | /* select#1 */ select '1' AS `id`,'film1' AS `name` from dual | +-------+------+---------------------------------------------------------------+
eq_ref：primary key 或 unique key 索引的全部部分被鏈接使用 ，最多隻會返回一條符合條件的記錄。這多是在 const 以外最好的聯接類型了，簡單的 select 查詢不會出現這種 type。
mysql> explain select * from film_actor left join film on film_actor.film_id = film.id; +----+-------------+------------+--------+---------------+-------------------+---------+-------------------------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+------------+--------+---------------+-------------------+---------+-------------------------+------+-------------+ | 1 | SIMPLE | film_actor | index | NULL | idx_film_actor_id | 8 | NULL | 3 | Using index | | 1 | SIMPLE | film | eq_ref | PRIMARY | PRIMARY | 4 | test.film_actor.film_id | 1 | NULL | +----+-------------+------------+--------+---------------+-------------------+---------+-------------------------+------+-------------+
ref：相比 eq_ref，不使用惟一索引，而是使用普通索引或者惟一性索引的部分前綴，索引要和某個值相比較，可能會找到多個符合條件的行。
1. 簡單 select 查詢，name是普通索引（非惟一索引） mysql> explain select * from film where name = "film1"; +----+-------------+-------+------+---------------+----------+---------+-------+------+--------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+----------+---------+-------+------+--------------------------+ | 1 | SIMPLE | film | ref | idx_name | idx_name | 33 | const | 1 | Using where; Using index | +----+-------------+-------+------+---------------+----------+---------+-------+------+--------------------------+ 2.關聯表查詢，idx_film_actor_id是film_id和actor_id的聯合索引，這裏使用到了film_actor的左邊前綴film_id部分。 mysql> explain select * from film left join film_actor on film.id = film_actor.film_id; +----+-------------+------------+-------+-------------------+-------------------+---------+--------------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+------------+-------+-------------------+-------------------+---------+--------------+------+-------------+ | 1 | SIMPLE | film | index | NULL | idx_name | 33 | NULL | 3 | Using index | | 1 | SIMPLE | film_actor | ref | idx_film_actor_id | idx_film_actor_id | 4 | test.film.id | 1 | Using index | +----+-------------+------------+-------+-------------------+-------------------+---------+--------------+------+-------------+
ref_or_null：相似ref，可是能夠搜索值爲NULL的行。
mysql> explain select * from film where name = "film1" or name is null; +----+-------------+-------+-------------+---------------+----------+---------+-------+------+--------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+-------------+---------------+----------+---------+-------+------+--------------------------+ | 1 | SIMPLE | film | ref_or_null | idx_name | idx_name | 33 | const | 2 | Using where; Using index | +----+-------------+-------+-------------+---------------+----------+---------+-------+------+--------------------------+
index_merge：表示使用了索引合併的優化方法。 例以下表：id是主鍵，tenant_id是普通索引。or 的時候沒有用 primary key，而是使用了 primary key(id) 和 tenant_id 索引
mysql> explain select * from role where id = 11011 or tenant_id = 8888; +----+-------------+-------+-------------+-----------------------+-----------------------+---------+------+------+-------------------------------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+-------------+-----------------------+-----------------------+---------+------+------+-------------------------------------------------+ | 1 | SIMPLE | role | index_merge | PRIMARY,idx_tenant_id | PRIMARY,idx_tenant_id | 4,4 | NULL | 134 | Using union(PRIMARY,idx_tenant_id); Using where | +----+-------------+-------+-------------+-----------------------+-----------------------+---------+------+------+-------------------------------------------------+
range：範圍掃描一般出如今 in(), between ,> ,<, >= 等操做中。使用一個索引來檢索給定範圍的行。
mysql> explain select * from actor where id > 1; +----+-------------+-------+-------+---------------+---------+---------+------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+-------+---------------+---------+---------+------+------+-------------+ | 1 | SIMPLE | actor | range | PRIMARY | PRIMARY | 4 | NULL | 2 | Using where | +----+-------------+-------+-------+---------------+---------+---------+------+------+-------------+
index：和ALL同樣，不一樣就是mysql只需掃描索引樹，這一般比ALL快一些。
mysql> explain select count(*) from film; +----+-------------+-------+-------+---------------+----------+---------+------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+-------+---------------+----------+---------+------+------+-------------+ | 1 | SIMPLE | film | index | NULL | idx_name | 33 | NULL | 3 | Using index | +----+-------------+-------+-------+---------------+----------+---------+------+------+-------------+
ALL：即全表掃描，意味着mysql須要從頭至尾去查找所須要的行。一般狀況下這須要增長索引來進行優化了
mysql> explain select * from actor; +----+-------------+-------+------+---------------+------+---------+------+------+-------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------+---------+------+------+-------+ | 1 | SIMPLE | actor | ALL | NULL | NULL | NULL | NULL | 2 | NULL | +----+-------------+-------+------+---------------+------+---------+------+------+-------+
5. possible_keys列
這一列顯示查詢可能使用哪些索引來查找。
explain 時可能出現 possible_keys 有列，而 key 顯示 NULL 的狀況，這種狀況是由於表中數據很少，mysql認爲索引對此查詢幫助不大，選擇了全表查詢。
若是該列是NULL，則沒有相關的索引。在這種狀況下，能夠經過檢查 where 子句看是否能夠創造一個適當的索引來提升查詢性能，而後用 explain 查看效果。
6. key列
這一列顯示mysql實際採用哪一個索引來優化對該表的訪問。
若是沒有使用索引，則該列是 NULL。若是想強制mysql使用或忽視possible_keys列中的索引，在查詢中使用 force index、ignore index。
7. key_len列
這一列顯示了mysql在索引裏使用的字節數，經過這個值能夠算出具體使用了索引中的哪些列。
舉例來講，film_actor的聯合索引 idx_film_actor_id 由 film_id 和 actor_id 兩個int列組成，而且每一個int是4字節。經過結果中的key_len=4可推斷出查詢使用了第一個列：film_id列來執行索引查找。
mysql> explain select * from film_actor where film_id = 2; +----+-------------+------------+------+-------------------+-------------------+---------+-------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+------------+------+-------------------+-------------------+---------+-------+------+-------------+ | 1 | SIMPLE | film_actor | ref | idx_film_actor_id | idx_film_actor_id | 4 | const | 1 | Using index | +----+-------------+------------+------+-------------------+-------------------+---------+-------+------+-------------+
key_len計算規則以下：
- 字符串
- char(n)：n字節長度
- varchar(n)：2字節存儲字符串長度，若是是utf-8，則長度 3n + 2
- 數值類型
- tinyint：1字節
- smallint：2字節
- int：4字節
- bigint：8字節
- 時間類型
- date：3字節
- timestamp：4字節
- datetime：8字節
- 若是字段容許爲 NULL，須要1字節記錄是否爲 NULL
索引最大長度是768字節，當字符串過長時，mysql會作一個相似左前綴索引的處理，將前半部分的字符提取出來作索引。
8. ref列
這一列顯示了在key列記錄的索引中，表查找值所用到的列或常量，常見的有：const（常量），func，NULL，字段名（例：film.id）
9. rows列
這一列是mysql估計要讀取並檢測的行數，注意這個不是結果集裏的行數。
10. Extra列
這一列展現的是額外信息。常見的重要值以下：
distinct: 一旦mysql找到了與行相聯合匹配的行，就再也不搜索了
mysql> explain select distinct name from film left join film_actor on film.id = film_actor.film_id; +----+-------------+------------+-------+-------------------+-------------------+---------+--------------+------+------------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+------------+-------+-------------------+-------------------+---------+--------------+------+------------------------------+ | 1 | SIMPLE | film | index | idx_name | idx_name | 33 | NULL | 3 | Using index; Using temporary | | 1 | SIMPLE | film_actor | ref | idx_film_actor_id | idx_film_actor_id | 4 | test.film.id | 1 | Using index; Distinct | +----+-------------+------------+-------+-------------------+-------------------+---------+--------------+------+------------------------------+
Using index：這發生在對錶的請求列都是同一索引的部分的時候，返回的列數據只使用了索引中的信息，而沒有再去訪問表中的行記錄。是性能高的表現。
mysql> explain select id from film order by id; +----+-------------+-------+-------+---------------+---------+---------+------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+-------+---------------+---------+---------+------+------+-------------+ | 1 | SIMPLE | film | index | NULL | PRIMARY | 4 | NULL | 3 | Using index | +----+-------------+-------+-------+---------------+---------+---------+------+------+-------------+
Using where：mysql服務器將在存儲引擎檢索行後再進行過濾。就是先讀取整行數據，再按 where 條件進行檢查，符合就留下，不符合就丟棄。
mysql> explain select * from film where id > 1; +----+-------------+-------+-------+---------------+----------+---------+------+------+--------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+-------+---------------+----------+---------+------+------+--------------------------+ | 1 | SIMPLE | film | index | PRIMARY | idx_name | 33 | NULL | 3 | Using where; Using index | +----+-------------+-------+-------+---------------+----------+---------+------+------+--------------------------+
Using temporary：mysql須要建立一張臨時表來處理查詢。出現這種狀況通常是要進行優化的，首先是想到用索引來優化。
1. actor.name沒有索引，此時建立了張臨時表來distinct mysql> explain select distinct name from actor; +----+-------------+-------+------+---------------+------+---------+------+------+-----------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------+---------+------+------+-----------------+ | 1 | SIMPLE | actor | ALL | NULL | NULL | NULL | NULL | 2 | Using temporary | +----+-------------+-------+------+---------------+------+---------+------+------+-----------------+ 2. film.name創建了idx_name索引，此時查詢時extra是using index,沒有用臨時表 mysql> explain select distinct name from film; +----+-------------+-------+-------+---------------+----------+---------+------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+-------+---------------+----------+---------+------+------+-------------+ | 1 | SIMPLE | film | index | idx_name | idx_name | 33 | NULL | 3 | Using index | +----+-------------+-------+-------+---------------+----------+---------+------+------+-------------+
Using filesort：mysql 會對結果使用一個外部索引排序，而不是按索引次序從表裏讀取行。此時mysql會根據聯接類型瀏覽全部符合條件的記錄，並保存排序關鍵字和行指針，而後排序關鍵字並按順序檢索行信息。這種狀況下通常也是要考慮使用索引來優化的。
1. actor.name未建立索引，會瀏覽actor整個表，保存排序關鍵字name和對應的id，而後排序name並檢索行記錄 mysql> explain select * from actor order by name; +----+-------------+-------+------+---------------+------+---------+------+------+----------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------+---------+------+------+----------------+ | 1 | SIMPLE | actor | ALL | NULL | NULL | NULL | NULL | 2 | Using filesort | +----+-------------+-------+------+---------------+------+---------+------+------+----------------+ 2. film.name創建了idx_name索引,此時查詢時extra是using index mysql> explain select * from film order by name; +----+-------------+-------+-------+---------------+----------+---------+------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+-------+---------------+----------+---------+------+------+-------------+ | 1 | SIMPLE | film | index | NULL | idx_name | 33 | NULL | 3 | Using index | +----+-------------+-------+-------+---------------+----------+---------+------+------+-------------+
使用的表
以上全部sql使用的表和數據：
DROP TABLE IF EXISTS `actor`; CREATE TABLE `actor` ( `id` int(11) NOT NULL, `name` varchar(45) DEFAULT NULL, `update_time` datetime DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8; INSERT INTO `actor` (`id`, `name`, `update_time`) VALUES (1,'a','2017-12-22 15:27:18'), (2,'b','2017-12-22 15:27:18'), (3,'c','2017-12-22 15:27:18'); DROP TABLE IF EXISTS `film`; CREATE TABLE `film` ( `id` int(11) NOT NULL AUTO_INCREMENT, `name` varchar(10) DEFAULT NULL, PRIMARY KEY (`id`), KEY `idx_name` (`name`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8; INSERT INTO `film` (`id`, `name`) VALUES (3,'film0'),(1,'film1'),(2,'film2'); DROP TABLE IF EXISTS `film_actor`; CREATE TABLE `film_actor` ( `id` int(11) NOT NULL, `film_id` int(11) NOT NULL, `actor_id` int(11) NOT NULL, PRIMARY KEY (`id`), KEY `idx_film_actor_id` (`film_id`,`actor_id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8; INSERT INTO `film_actor` (`id`, `film_id`, `actor_id`) VALUES (1,1,1),(2,1,2),(3,2,1);
參考 mysql 官網：https://dev.mysql.com/doc/refman/5.7/en/explain-output.html
相關文章
- 1. MySQL explain詳解
- 2. MySQL - EXPLAIN詳解
- 3. MySQL Explain詳解
- 4. mysql explain 詳解
- 5. Mysql Explain 詳解
- 6. Mysql Explain詳解
- 7. MySQL EXPLAIN詳解
- 8. MySQL explain 詳解
- 9. MySQL EXPLAIN 詳解
- 10. mysql explain詳解
- 更多相關文章...
- • SQLite Explain（解釋） - SQLite教程
- • MySQL子查詢詳解 - MySQL教程
- • Flink 數據傳輸及反壓詳解
- • 漫談MySQL的鎖機制
相關標籤/搜索
每日一句
-
每一个你不满意的现在，都有一个你没有努力的曾经。
最新文章
- 1. 安裝cuda+cuDNN
- 2. GitHub的使用說明
- 3. phpDocumentor使用教程【安裝PHPDocumentor】
- 4. yarn run build報錯Component is not found in path 「npm/taro-ui/dist/weapp/components/rate/index「
- 5. 精講Haproxy搭建Web集羣
- 6. 安全測試基礎之MySQL
- 7. C/C++編程筆記：C語言中的複雜聲明分析，用實例帶你完全讀懂
- 8. Python3教程(1)----搭建Python環境
- 9. 李宏毅機器學習課程筆記2：Classification、Logistic Regression、Brief Introduction of Deep Learning
- 10. 阿里雲ECS配置速記
歡迎關注本站公眾號,獲取更多信息
相關文章
- 1. MySQL explain詳解
- 2. MySQL - EXPLAIN詳解
- 3. MySQL Explain詳解
- 4. mysql explain 詳解
- 5. Mysql Explain 詳解
- 6. Mysql Explain詳解
- 7. MySQL EXPLAIN詳解
- 8. MySQL explain 詳解
- 9. MySQL EXPLAIN 詳解
- 10. mysql explain詳解