What is the '=*' Operator in Older Versions of Microsoft SQL Server and Why is it Deprecated?

Exploring the Mysterious "=*" Operator in Microsoft Server SQL

While delving into the intricacies of Microsoft Server SQL, you may stumble upon an uncommon syntax in a join operation. The "=" symbol followed by the asterisk (), written as "=", has left many puzzled. To shed light on this enigmatic notation, let us uncover its true meaning.

In SQL Server versions prior to 2005, the "=" operator served a specific purpose in the context of outer joins. Unlike the standard ANSI JOIN syntax, the "=" syntax denoted a special type of outer join that is no longer supported in modern versions of SQL Server.

In its essence, this syntax compares the values in two specified columns across tables. For instance, the following code snippet illustrates the use of "=*" in an outer join:

WHERE table1.yr =* table2.yr -1

Here, the "=*" operator will perform a comparison between the "yr" column of "table1" and the "yr" column of "table2" shifted by one year backwards. This particular usage allows developers to obtain rows from "table1" that match "table2" one year after the specified year range.

However, with the advent of SQL Server 2005 and subsequent versions, the "=" syntax for outer joins was deprecated in favor of more standardized and cross-platform compatible operators such as OUTER JOIN. As a result, for modern SQL development, it is recommended to refrain from using "=" and instead adopt contemporary ANSI JOIN syntax to ensure optimal compatibility and readability.

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