assign value to variable in sql select statement

There are two ways to assign values to variables that are already defined in SQL Server, SET and SELECT, respectively.The differences between these two approaches are explained in more detail in SQL Server Books Online, but many times weDid not notice, in fact, these two ways still have a lot of differences.SQL Server

execution plan.Seek by the clustered index finds a row and then begins the update. Note here that when update is applied, it will apply for an X lock for clustered index.In fact, here we understand why update creates a deadlock on select. Update, will apply for a clustered index x lock, so blocked (note, not a deadlock!) The last clustered in the Select Index Seek. Where is the other half of the deadlock?

Original post address: http://blog.csdn.net/wangyihust/archive/2009/02/05/3863758.aspx select 1 from table; and select anycol (any row in the destination table set) from table; and select * from table in terms of function is no difference, it is used to check whether there are records. It is generally used for conditional query. 1 in

|+ -------- +| James || Li Si || Wang Wu || Zhao Liu |+ -------- + Didn't the duplicate Rows be removed? (3) subquery nesting and SQL statement execution sequence Analyze the problem above: There are two subquery select statements, the outer select queries the inner select

We have been paying little attention to the execution sequence of Select statements in SQL, and we are very casual about the use of keywords. As for the efficiency problem, because the data volume in the table is not very large, so I am not very concerned about it. We have been paying little attention to the execution sequence of Select statements in

functions for data summarization using GROUP by Select sum (UnitPrice) as [ SUM ] from Products Select CategoryID, sum (UnitPrice) as [ SUM ] from Products Group by CategoryID 2) The column of the query must be a class that appears in group by 3) must be queried in the order of the conditional

Select 1 from... what does 1 in an SQL statement mean? What is the result? Select 1 from table; and select anycol (any row in the target table set) from table; there is no difference between select * from table and

like ' t% ';SELECT * from emp where ename ' t% ';SELECT * from emp where ename like '%t% ';SELECT * from emp where ename '%t% ';SELECT * from emp where sal! = 1000=SELECT * from emp where Sal 2.5 Logical operatorsBoolean operation (Boolean) evaluates to: TRUE, FALSENon-OR a

Oracle database, BULK INSERT data with mybatic: "Node_data" ("node_id", "Data_time", "Data_v Alue "," Data_number ", "Data_version", "INVALID" ) #{item.nodeid, Jdbctype=varchar}, #{item.datatime, jdbctype=}, # {item.datanumber, jdbctype=NUMERIC}, #{item.dat