if statement in select query

of data, some forms of where clauses force the optimizer to use sequential access to invalidate the original index fields. Eg :... Where (O. D = 123 and O. a> 200) Union O. B = 1010 efficiency higher than where (O. D = 123 and O. (B> 200) or O. B = 1010 V. Temporary tables: Use temporary tables to accelerate queries Sort a subset of a table and create a temporary table, which sometimes accelerates query. Note: after a temporary table is create

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Select * From Table Where A. tenantkey = @ Tenantid And ( @ Projectkeys Is Null Or B. recuritprojectkey In (Select * From DBO. f_splittoint ( @ Projectkeys , ' , ' ))) And ( @ Projectdutyuserkeys Is Null Or B. projectdutyuserkey In ( Select * From DBO. f_splittoint ( @ Projectdutyuserkeys , ' , ' ))) When two parameters, @ projec

When we query information in the database, we often need to query the information based on the conditions entered by the user. Some conditions are available, but some conditions are unavailable. Therefore, we need to assemble the condition statements. The following method is compiled based on this situation, hoping to help the reader: String SQL = "select * fr

For example, in the employee basic information table, there are employee names, employee positions, birth dates, and so on. If the three fields in the current view are displayed in the same field, there is a delimiter in the middle. For example, I want to display the result as "Manager Victor was born in May 3, 1976 ". What should we do? In fact, this is relatively simple. We can use the connector to connect these fields in the Select

If we use the Select statement to query data from the database, how does the Oracle database work? What can we learn from this? Next, we will combine a simple select statement to look at the operating mechanism of the Oracle database background. This is very helpful for syst

] [1] as shown in, if you write this statement, the query statement in the value will be executed multiple times, resulting in slow access. What should I do to solve this problem? I think so, but I don't know, right. 1. I directly group all the required data in the controller and then upload it to DynaGr... ] [1] As shown in, this write operation will execute t

We use the Select COUNT (*) statement when we generally count database records, and when we use Query Analyzer for SQL Server, the direct input to the SELECT count (*) from table name counts the records in the table. But how do we return the value when we use ASP to implement it? How do you output the total number of r

---------- --------- ---------- -------------- ---------- DEPTNO ---------- 7839 king president 17-11 month-81 5000 10 3. Analysis 1. the user process executes a statement, such as select * from emp where empno = 7839; 2. the user process has established a connection with the server process and stored the user process information in the UGA of PGA. 3. The stateme