当前使用了半连接LooseScan策略,详见https://mariadb.com/kb/en/loosescan-strategy/,翻译http://www.javacoder.cn/?p=39 No matching min/max row 没有任何能满足例如 SELECT MIN(…) FROM … WHERE condition 中的condition的行。 no matching row in const table 对于关联查询,存在一个空表,或者没有行...
{EXPLAIN|DESCRIBE|DESC}tbl_name[col_name|wild]{EXPLAIN|DESCRIBE|DESC}[explain_type]{explainable_stmt|FORCONNECTIONconnection_id}{EXPLAIN|DESCRIBE|DESC}ANALYZEselect_statementexplain_type:{FORMAT=format_name}format_name:{TRADITIONAL|JSON|TREE}explainable_stmt:{SELECTstatement|TABLEstatement|DELETEstatement|I...
explainable_stmt: {SELECTstatement|TABLEstatement|DELETEstatement|INSERTstatement|REPLACE statement|UPDATEstatement } 示例: EXPLAIN format=TRADITIONAL jsonSELECTtt.TicketNumber, tt.TimeIn, tt.ProjectReference, tt.EstimatedShipDate, tt.ActualShipDate, tt.ClientID, tt.ServiceCodes, tt.RepetitiveID, tt.Curr...
In C#, the switch statement serves as a control structure that enables the execution of distinct code blocks based on the value of a variable. It is frequently utilized when there is a need to compare a variable with multiple constant values and to carry out various actions according to the...
8 unique_subquery:该类型和eq_ref类似,但是使用了IN查询,且子查询是主键或者唯一索引。例如: value IN (SELECT primary_key FROM single_table WHERE some_expr) 9 index_subquery:和unique_subquery类似,只是子查询使用的是非唯一索引 value IN (SELECT key_column FROM single_table WHERE some_expr) ...
EXPLAIN Statement Extended EXPLAIN Output Format Estimating Query Performance MySQL中explain执行计划中额外信息字段(Extra)详解 explain参数详解 最官方的 mysql explain type 字段解读 What does eq_ref and ref types mean in MySQL explain 面试官:不会看 Explain执行计划,简历敢写 SQL 优化?
SET optimizer_switch = 'index_condition_pushdown=off'; SET optimizer_switch = 'index_condition_pushdown=on'; 开或者关闭索引条件下推,并对比: explain SELECT * FROM people WHERE zipcode='95054' AND lastname LIKE '%etrunia%' AND address LIKE '%Main Street%'; 的执行结果。 index condition ...
Consider the statement:int a= 10,20,30;It is a declaration with initialization statement and here comma is a separator and we cannot use values like this. This will be correct output (which is a compile time error): main.cpp: In function ‘int main()’: ...
Combo Box and switch statement combo box using display and internal value? combo box with default value and text in c#? ComboBox / Dictionary and the "Key" value Combobox control return System.NullReferenceException: Object reference not set to an instance of an object ComboBox DisplayMember ...
contains = "bear"; } if (colour === "red" || colour === "blue"){ // colour is either red or blue } // The `switch` statement checks for equality with `===`. // use 'break' after each case // or the cases after the correct one will be executed too. grade = 'B'; ...