When does the predicate is null succeed

You may have heard of the word, SARGable. In brief, it’s a term derived from the phrase, Search ARGument able, and relates to SQL Server’s ability to seek through an index for a predicate. Non-sargable predicatescould lead to poor query performance which is why it’s important to understand this. Sargability can be affected with the use of functions in the WHERE, ORDER BY, GROUP BY and HAVING clauses. There are a number of articles that talk about sargability but we are going to focus just on the ISNULL function and it’s effect on sargability in this article. There is something quite interesting in store too. I will be running some queries against the StackOverflow database in order to present this. Let’s start by running the following query SELECT TOP 10 Id FROM Users WHERE Age > 18 Before looking at the execution plan, I think it’s important to know the schema and the index available. The execution plan looks as follows, just as you would expect. Now let’s run the following query SELECT TOP 10 Id FROM Users WHERE ISNULL(Age, 0) > 18 Note the ISNULL function on the column ‘Age’ in the WHERE clause. Let’s look at the execution plan as well. We are now doing a scan on the non-clustered index instead of a seek, because SQL does not think the predicate is sargable any more. You might think “Why the non-clustered index?” Since the non-clustered index is the smallest index available to SQL Server that provides all the column it requires to run the query, it does not need to scan...

It appears that my LinqKit Predicatebuilder function breaks when either the FirstName or LastName value = null. public partial class Student How do I rewrite predicate.Or(s => searchTerms.Any(srch => s.FirstName.Contains(srch))); since Contains requires a value to search and throws an exception? I've tried: predicate = predicate.Or(s => searchTerms.Any(srch => s.FirstName == null ? false : s.FirstName.Contains(srch))); and also predicate = predicate.Or(s => searchTerms.Any(srch => s.FirstName == null ? true : s.FirstName.Contains(srch))); which compiles but now the FirstName is not searched. Use the Contains if FirstName is not null, avoiding the exception. searchTerms.Any(srch => s.FirstName?.Contains(srch) == true)); The explicit == true is necessary as this evaluates to a bool? and not a bool. For LINQ providers that don't support this operator it's effectively the same as searchTerms.Any(srch => s.FirstName == null ? false : s.FirstName.Contains(srch));

This set of RDBMS Multiple Choice Questions & Answers (MCQs) focuses on “Set Operations”. 1. What is the function of the union operation? a) It combines the results of any two different queries b) It combines the results of two different queries which have the same set of attributes in the select clause c) It combines the results of two different queries which have the same condition in the where clause d) It gives the Cartesian product of the results of any 2 queries View Answer 2. What is the function of the intersect operation? a) It returns the intersection of the results of the results of any two different queries b) It returns the intersection of the results of two different queries which have the same set of attributes in the select clause c) It returns the intersection of the results of two different queries which have the same condition in the where clause d) None of the mentioned View Answer Answer: b Explanation: The intersect operation returns the intersection of the results of the results of two different queries which have the same set of attributes in the select clause. It automatically eliminates duplicates. 3. What is the function of the except operation? a) It excludes all the results present in both the queries b) It includes the results of the second query but excludes the results of the first query c) It includes the results of the first query but excludes the results of the second query d) It includes all the results of both queries but removes duplic...

Quite often I see queries that are not sargable due to the use of the ISNULL function in the query’s predicate (WHERE clause) The demo query This is the query we will use to demonstrate the problem with the ISNULL function: select CustomerID ,NameStyle ,Title ,FirstName ,MiddleName ,LastName ,Suffix ,CompanyName ,SalesPerson ,EmailAddress ,Phone ,PasswordHash ,PasswordSalt ,rowguid ,AccountNbr ,ModifiedDate from CustomerAccount where isnull(AccountNbr, '')='' This query is looking for any records where the AccountNbr column is empty or NULL. From looking at the execution plan we’ll see that there is a scan on the AccountNbr column: This query, based on estimates will return one row but according to the plan it is reading about 3.6 million rows to find this. This version of the query takes 9 seconds on average to execute. In general applying a function to a column in a predicate (where clause) causes an index to be unusable (unsargable). This is not always the case, but most of the time it works this way. In many cases queries that have unsargable predicates can be rewritten to make them sargable. Rewritten query (and now it’s sargable) It is recommended that if you are looking for NULL values you should use the IS NULL operator instead of the ISNULL function. Don’t just take my word for it, Microsoft suggests it in their documentation as well: Here is the query where it was rewritten to use IS NULL. select CustomerID ,NameStyle ,Title ,FirstName ,MiddleName ,LastName ,Suff...

• How It Works • Overview Robust, real-time communication assistance • Generative AI Write, rewrite, get ideas, and quickly reply with GrammarlyGO • Writing Enhancements Features to polish, grammar, tone, clarity, team consistency, and more • Trust & Security You own your data • Demo Try Grammarly, and see how it works • Where It Works • Overview Writing assistance on 500,000+ apps and sites across your devices • Windows & Mac For desktop apps and websites like Word and Gmail • Browser Extension For sites like Google Docs, Gmail, and LinkedIn • Mobile For every Android and iOS app • Who We Are • About • Responsible AI • Press • Careers • We Stand with Ukraine • • Tools • Demo Try Grammarly, and see how it works • Grammar Checker Check for grammar, spelling, and punctuation mistakes • Plagiarism Checker Check your work for plagiarism • Citation Generator Format citations in APA, MLA, and Chicago • Essay Checker Review your papers for a better grade • Guides • Writing • Grammar • Punctuation • Blog A predicate is the grammatical term for the words in a sentence or clause that describe the action but not the subject. In other words, the predicate explains what the subject does. For all intents and purposes, a predicate includes all the words in a sentence or clause except the subject (and words that modify the subject). Predicates are one of the core building blocks of English sentences, so it’s good to understand how they work. Below, we answer your questions like, What is a...

In a general sense you could say almost all SQL issues are in some way related to misapplied predicates. In this article I’ll focus on two classes of problems. The first would be queries where there is confusion between join predicates and filtering predicates. The second type of problem is with the predicates that are unable to be pushed. Before digging in too deep it’s probably a good idea to explain what a predicate is. They are logical conditions such as those found in the WHERE or ON clauses of a query. A few simple examples: WHERE col3 in (‘a’,’b’,’c’) tab1 JOIN tab2 ON tab1.id = tab2.parent_id WHERE x.col1 > y.col2 In those, the first is a filtering predicate, the second is a join predicate. The third is also a join predicate but may be harder to distinguish because it is embedded within a WHERE clause rather than an ON clause. These logical conditions are distinct from those found in a CASE statement because the predicates control which rows are returned by a query, whereas the conditions of a CASE statement control how columns within rows are processed. It is legal to use a CASE statement within a join or filtering predicate but that is an extra layer of complexity that is often avoidable. I’ll discuss this condition later in the section on pushing predicates. Join Predicates Every join is Cartesian When someone comes to me with a problem where their query returns too many rows and/or duplicate rows I use a simple mnemonic to remind myself of one of the possible c...

Returns a composed predicate that represents a short-circuiting logical AND of this predicate and another. When evaluating the composed predicate, if this predicate is false, then the other predicate is not evaluated. Any exceptions thrown during evaluation of either predicate are relayed to the caller; if evaluation of this predicate throws an exception, the other predicate will not be evaluated. Parameters: other - a predicate that will be logically-ANDed with this predicate Returns: a composed predicate that represents the short-circuiting logical AND of this predicate and the other predicate Throws: • negate default Returns a composed predicate that represents a short-circuiting logical OR of this predicate and another. When evaluating the composed predicate, if this predicate is true, then the other predicate is not evaluated. Any exceptions thrown during evaluation of either predicate are relayed to the caller; if evaluation of this predicate throws an exception, the other predicate will not be evaluated. Parameters: other - a predicate that will be logically-ORed with this predicate Returns: a composed predicate that represents the short-circuiting logical OR of this predicate and the other predicate Throws:

The ALL, SOME and ANY predicates aren't much used in SQL Server, but they are there. You can use the Exists() predicate instead but the logic is more contorted and difficult to read at a glance. Set-oriented predicates can greatly simplify the answering of many real-life business questions, so it is worth getting familiar with them. Joe Celko explains. You’ve probably read that SQL is a language based on sets and predicates. Well, that sounds impressive but what does it really mean? It means that we ought to have some predicates that use sets as their operands. And we do; but a lot of them are a bit obscure and not often used. All of them can be written with the [NOT] EXISTS () predicate and other logical operators in correlated subqueries. While that is perfectly OK, the results can be a bit hard to read. Let us examine some of these features and see how we can use them. The [NOT] EXISTS() Predicate I am going to assume by now that you have seen an EXISTS() predicate in SQL. , but perhaps you do not yet fully appreciate it. It existed at the very start of the language, and it has a nice intuitive meaning. This is because it is one of the few predicates that we have, perhaps the only one, that evaluates to either TRUE and FALSE, but never UNKNOWN. The current BNF is very simple. ::= EXISTS Originally, the had to be a one column table. This is because the EXISTS() predicate was defined in the same part of the standard that gave us the “ ALL ” and “ [SOME|ANY] ” predica...