"(SELECT id FROM users WHERE user_id = :user_id AND appointment_id = :appointment_id) UNION ...
mysql> EXPLAIN FORMAT=tree SELECT * FROM s1 INNER JOIN s2 ON s1.key1 = s2.key2 WHEREs1.common_field = 'a'\G*** 1. row ***EXPLAIN: -> Nested loop inner join (cost=1360.08 rows=990)-> Filter: ((s1.common_field = 'a') and (s1.key1 is not null)) (cost=1013.75rows=990)...
下面是一个使用if嵌套语句的存储过程示例: delimiter//createproceduretest_if_nested(instudent_namevarchar(50),outresult_msgvarchar(50) )begindeclarestudent_scoreint;selectscoreintostudent_scorefromstudentwherename=student_name; if(student_score>=90)thensetresult_msg='优秀'; if(student_score=100)thenset...
The SELECT identifier. This is the sequential number of the SELECT within the query. The value can be NULL if the row refers to the union result of other rows. In this case, the table column shows a value like <unionM,N> to indicate that the row refers to the union of the rows wi...
SELECT * FROM TABLE WHERE a=xxx AND b=xxx ORDER BY c; 但是对于下面的语句,联合索引不能直接得到结果,其还需要执行一次 filesort 排序操作,因为索引(a,c)并未排序: CREATE TABLE buy_log_01( a INT UNSIGNED NOT NULL, b INT default NULL, ...
EXPLAIN works with SELECT, DELETE, INSERT, REPLACE, and UPDATE statements. EXPLAIN与SELECT、DELETE、INSERT、REPLACE和UPDATE语句一起工作。 When EXPLAIN is used with an explainable statement, MySQL displays information from the optimizer about the statement execution plan. That is, MySQL explains how it...
"(SELECT id FROM users WHERE user_id = :user_id AND appointment_id = :appointment_id) UNION ...
| UPDATE statement } 2.2 示例 EXPLAIN format = TRADITIONAL json SELECT tt.TicketNumber, tt.TimeIn, tt.ProjectReference, tt.EstimatedShipDate, tt.ActualShipDate, tt.ClientID, tt.ServiceCodes, tt.RepetitiveID, tt.CurrentProcess, tt.CurrentDPPerson, ...
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, ...
SELECTid,dataINTO@x,@yFROMtest.t1LIMIT1; INTOvar_listcan also be used with aTABLEstatement, subject to these restrictions: The number of variables must match the number of columns in the table. If the table contains more than one row, you must useLIMIT 1to limit the result set to a ...