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When to use the where clause in SQL Server?
If you invoke a function call on a value from a row in the query it will need to call the function for each row in the query. So for this example it has to evaluate each StartTime value to see if this is true. Buf it you use a function that returns only one value it will get run once.
How to avoid functions in the where clause?
Not using functions in the WHERE clause is a simple thing to avoid and can provide big performance gains if use alternative methods. Look for poor performing statements in your databases where scans are occurring to see if functions are being used in the WHERE clause
When to use upper clause in SQL Server?
Here is another example where the UPPER clause is used to transform the EmailAddress into upper case before evaluating the data. Again the EmailAddress is indexed. We can see that the query plan for this also does an index scan versus an index seek.
When to use functions in the SELECT clause?
When functions are used in the SELECT clause, the function has to be run with each data value to return the proper results. This may not be a bad thing if you are only returning a handful of rows of data.
Introduction to SQL Server WHERE clause. When you use the SELECT statement to query data against a table, you get all the rows of that table, which is unnecessary because the application may only process a set of rows at the time. To get the rows from the table that satisfy one or more conditions, you use the WHERE clause as follows:
How to optimize conditional where clauses in SQL?
Often when you use conditional WHERE clauses you end upp with a vastly inefficient query, which is noticeable for large datasets where indexes are used. A great way to optimize the query for different values of your parameter is to make a different execution plan for each value of the parameter. You can achieve this using OPTION (RECOMPILE).
What are some tips and tricks for SQL Server?
Tips and tricks. SQL Server can efficiently filter a data set using indexes via the WHERE clause or any combination of filters that are separated by an AND operator. By being exclusive, these operations take data and slice it into progressively smaller pieces, until only our result set remains. OR is a different story.
Which is the search condition in the where clause?
In the WHERE clause, you specify a search condition to filter rows returned by the FROM clause. The WHERE clause only returns the rows that cause the search condition to evaluate to TRUE. The search condition is a logical expression or a combination of multiple logical expressions. In SQL, a logical expression is often called a predicate.