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What is STATISTICS XML in SQL Server?

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In SQL Server, you can use the SET STATISTICS XML statement to generate detailed information about how a T-SQL statement was executed.

This information is provided in the form of a well formed XML document.

Once SET STATISTICS XML is set to ON, each subsequent statement is reflected in the output by a single XML document.

Each XML document contains the text of the statement, followed by the details of the execution steps.

The output shows run-time information such as the costs, accessed indexes, and types of operations performed, join order, the number of times a physical operation is performed, the number of rows each physical operator produced, and more.

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How SHOWPLAN_XML Works in SQL Server

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In SQL Server, you can use the SET SHOWPLAN_XML statement to return the query plan for a T-SQL statement in the form of a well-defined XML document. The query plan contains detailed information about how the statement will be executed.

It’s similar to SHOWPLAN_ALL, except that SHOWPLAN_ALL returns its data set of rows that form a hierarchical tree.

You can set SHOWPLAN_XML to either ON or OFF.

When SHOWPLAN_XML is ON, all subsequent T-SQL statements are not executed. Instead SQL Server returns execution information for the statement (without executing it).

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3 Ways to use ALL in SQL Server

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You might be familiar with the ALL option in SQL Server. Perhaps you’ve used it along with the UNION operator to include any duplicates that might be returned in the result set.

But did you know that ALL can also be used in two other contexts?

ALL can be used in the following three contexts:

  • As an argument to the SELECT clause.
  • As an argument to the UNION clause.
  • As a logical operator when comparing a scalar value with a single-column set of values.

Examples of each of these contexts follows.

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SQL Server ALL Operator Explained

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In SQL Server, the ALL operator can be used with a subquery to compare a scalar value with a single-column set of values returned by the subquery.

It’s also true that the SELECT clause and UNION operator both accept an ALL argument, although this usage has a different purpose (allows duplicates in the result set).

Below are examples of using the ALL operator with a subquery.

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What is a Comparison Operator?

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Comparison operators are an important part of most programming languages.

Comparison operators are used to compare two expressions. The result is either true or false. It could also be unknown. This could also be represented by either 1, 0, or NULL, depending on the language. These are typically known as “Boolean expressions”.

When used with databases, comparison operators can be used inside your SQL queries to filter data to a certain criteria.

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How IIF() Works in SQL Server

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In SQL Server, the IIF() function (not to be confused with the IF statement) is a conditional function that returns the second or third argument based on the evaluation of the first argument.

It’s a shorthand way for writing a CASE expression. It’s logically equivalent to CASE WHEN X THEN Y ELSE Z END assuming IIF(X, Y, Z).

IIF() is an abbreviation for Immediate IF.

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How the IF Statement Works in SQL Server

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Most (probably all) programming languages include some form of the IF statement that allows programmers to write conditional code. That is, code that will execute only if a certain condition is true.

It’s a very simple concept. Basically it goes like this:

“If this, do that.”

Most languages simply call it IF, but some have their own twist on the name (for example, in ColdFusion/CFML, it’s called CFIF).

In any case, they essentially do the same thing.

In SQL Server (or more precisely, its programming language T-SQL) it’s called IF.

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