B:const:使用唯一索引或者主键,返回记录一定是1行记录的等值where条件时,通常type是const。其他数据库也叫做唯一索引扫描 C:eq_ref:出现在要连接过个表的查询计划中,驱动表只返回一行数据,且这行数据是第二个表的主键或者唯一索引,且必须为not null,唯一索引和主键是多列时,只有所有的列都用作比较时才会出现eq_...
in:当B表的数据集小于A表的数据集时,in优于exists select*fromAwhereidin(selectidfromB) #等价于:for(selectidfromB){select*fromAwhereA.id=B.id } exis`ts:当A表的数据集小于B表的数据集时,exists优于in 将主查询A的数据,放到子查询B中做条件验证,根据验证结果(true或false)来决定主查询的数据是否保...
WITH(DATA_COMPRESSION=PAGE);</sql_operation>25</sql_operations>26</dsql_operation>27<dsql_operationoperation_type="BROADCAST_MOVE">28<operation_costcost="0.121431552"accumulative_cost="0.121431552"average_rowsize="16"output_rows="31.6228"/>29SELECT [T1_1].[CustomerKey] AS [CustomerKey], 30 ...
form MUST be utilized for all representations of the data model in the base media type, `application/vc+ld+json`. Syntactic Sugar0 comments on commit 1090e2e Please sign in to comment. Footer © 2023 GitHub, Inc. Footer navigation Terms...
这是一个简单的查询 table 查询的是lm_d_plan 表 type ref常见连接查询,一个表是基于索引的查找 possible_keys 可能用到的索引是FK_deptNo key 使用的索引是FK_deptNo key_len 索引的长度是99 ref lms.lm_c_dept.deptNo这列索引被使用了 rows 需要扫描的行数3968 Extra 使用索引 2 rows in set (0.00 ...
Specifies the database that contains the new EXPLAIN tables. The stored procedure creates the database if it does not exist. The data type of this input parameter is VARCHAR(8). If this option is not specified, the stored procedure omits the database and table space names in the CREATE TA...
type显示的是访问类型,是较为重要的一个指标,结果值从好到坏依次是:system > const > eq_ref > ref > fulltext > ref_or_null > index_merge > unique_subquery > index_subquery > range > index > ALL一般来说,得保证查询至少达到range级别,最好能达到ref。
Datatype -- What format the data is in, and what can be done to it. Data Value -- The actual value(s) a piece of data represents. For example, consider the simple Explain assignment statement: A = 1 The 'A' refers to a variable in which we've stored a value of 1. Later on ...
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从执行计划的type列的值是index_merge就可以看出,MySQL打算使用索引合并的方式来执行对s1表的查询。 unique_subquery 类似于两表连接中被驱动表的eq_ref访问方法,unique_subquery是针对在一些包含IN子查询的查询语句中,如果查询优化器决定将IN子查询转换为EXISTS子查询,而且子查询可以使用到主键进行等值匹配的话,那么该...