共返回1 行记录,花费 5 ms。 2. 场景解析 从查询条件中可以看出 token 和 uid 过滤性都非常好,但是由于使用了 or, 需要采用 index merge 的方法才能获得比较好的性能。但在实际执行过程中MySQL优化器默认选择了使用registrationId 上的索引,导致 SQL 的性能很差。 3. 场景优化 我们将SQL改写成union all的形式。
SQL的OR运算符用于根据多个条件筛选记录,只要有一个条件为TRUE,就会返回记录。下面是OR运算符的基本语法: 代码语言:sql AI代码解释 SELECTcolumn1,column2,...FROMtable_nameWHEREcondition1ORcondition2ORcondition3...; column1,column2,等是您要选择的列名称。 table_name是您从中选择记录的表的名称。 condition...
You execute a query that contains a search condition with, at least, two equality predicates on the same limited size character column (using either OR or IN clause). You define a varchar(max) variable and use it in...
Semaphore timeout: This error points to a timeout condition related to the use of semaphores in the network. The Wait Operation Timed Out: A wait operation has exceeded its allowed time, typically due to network delays. A fatal error occurred while reading the input stream from the ne...
If the updated row previously didn't meet the filter condition but meets the condition after the update, only the INSERT procedure call is sent through the replication process. In the preceding example, assume that you also have a horizontal filter defined on TABLE1: where col3 = '...
AndCondition Class Argument Class BetweenLeafCondition Class BooleanLeafCondition Class Condition Class ConditionTree Class ConstantValue Class ExpressionOperator Enumeration ExpressionValue Class FieldValue Class FilterAction Enumeration FilterRule Class FilterStatement Class FunctionValue Class InputType Class IsNull...
MergeCondition MergeSpecification MergeStatement MessageSender MessageTypeStatementBase MessageValidationMethod MethodSpecifier MigrationState MirrorToClause ModifyFileGroupOption MoneyLiteral MoveConversationStatement MoveRestoreOption MoveToDropIndexOption MultiPartIdentifier MultiPartIdentifierCallTarget Named...
Applies to:SQL Server Use this dialog box to create or change a Policy-Based Management condition. A condition is a Boolean expression that specifies a set of allowed states of a Policy-Based Management managed target with regard to facets. The properties tha...
The OR command is used with WHERE to include rows where either condition is true.The following SQL statement selects all fields from "Customers" where city is "Berlin" OR city is "München":ExampleGet your own SQL Server SELECT * FROM Customers WHERE City='Berlin' OR City='München'; ...
http://technet.microsoft.com/en-us/library/ms190766%28v=sql.105%29.aspx http://www.codeproject.com/Articles/265371/Common-Table-Expressions-CTE-in-SQL-SERVER So let’s start with pretty basic stuff. Regular Join Joiningtablewith itself based on condition, where onesparentIdis equal to anot...