As developers, we often use the clustering index and non-clustered index, if I ask most people the following two questions may have few satisfactory answers. What is the clustering index (clustered index) / What is non-clustering index (nonclustered index)? clustered index and non-clustered index What is the difference? In fact, the index can be understood … Continue reading
Using Variables Like C language, variables are divided into: Local variables: Local variables must be marked with @ as a prefix, such asage Use of local variables is the first statement, and then the assignment Global variables: Global variables must mark @@ as a prefix, such as @@version Global variables, we can only be read … Continue reading
Index Building Filter (filter when the index is created) There are some very inefficient index, such as regular query the status of ongoing orders, order 99% of the state is complete, one percent is in progress, so we built an index on the order status field, performance is improved, but the feeling in the index … Continue reading
This a good example of the co-related query. For example we have table with 5 employees and their salary. If we want to query the employee with second highest salary, we can use the query below.