Why does null not equal null

The veteran then points out that NULL is never equal to anything. This is where the language is confusing. The correct way to understand NULL is that it is not a value.

NULL is the complete, total absence of any value whatsoever. Short answer: NULL. Every time. See past emails here. Where are you finding NULL values? Though your original data does not have NULLs, there are two cases where your query can generate rows with NULL values: Outer joins, when you want to fill gaps in your data.

NULL values are a fact of life, and we should learn to deal with them. For example, select coalesce 'love', 'sql' ; -- returns love select coalesce null, 'love', 'sql' ; -- returns love 3b.

They spend thousands of dollars to get this level of detailed analysis — which you can now get for free. We send one update every week. Where in the sort order should they be? Like sorting, grouping is done as if all NULL values are considered equal, in contrast to the way that they are treated in an expression. They are collected into a single group. However, what if two rows both have NULL s for one or columns but are otherwise-identical? We can easily test this. The result is still , which is the number in the original table.

NULL values are an essential part of the relational database, because data can be both intentionally and unintentionally missing, and it can be unknown. It can never be correct. The expression will always return NULL. However these functions can be very handy, if used guardedly. NULL s can trip up a programmer, yet provide a very versatile way of handling data, providing a range of software devices for dealing successfully with commercial database processes and reports.

Find out more. However, it no longer has a clear performance advantage and should be avoided in production code. Louis Davidson explains how he manages and shares several different sources of SQL Prompt code snippets, in a single Snippet library, using Dropbox and source control.

It was provided purely for legacy databases that had code that assumed the old CHAR behavior for dealing with padding, and its use has now been deprecated. There are no advantages to using old-style join syntax. If SQL prompt identifies its use in legacy code, then rewriting the statements to use ANSI-standard join syntax will simplify and improve the code.

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