## 数据库（mssql）

»# Implementing Fuzzy Sets in SQL Server, Part 4: From Fuzzy Unions to Fuzzy Logic

………… First, let me get the code for fuzzy unions out of the way. To readers of the last article, the structure of Figures 1 through 4 ought to look familiar. Once again, I’m using the output of two stored procedures I wrote for Outlier Detection with SQL Server, part 2.1: Z-Scores and Outlier Detection with SQL Server, part 2.2: Modified Z-Scores as my membership functions (you can of course test it on other membership functions that have nothing to do with Z-Scores), then storing the results in two table variables. As usual, the GroupRank and OutlierCandidate columns can be safely ignored (they’re only included in the INSERT EXEC because they were part of the original procedures), while the ReversedZScore column is used in conjunction with the @RescalingMax, @RescalingMin and @RescalingRange variables to normalize the results on the industry-standard fuzzy set range of 0 to 1. In fact, there aren’t any differences whatsoever in the code till we insert the results of the union in a third table variable, so that we can demonstrate several T-conormswith it later on; in practice, it may be possible to perform fuzzy unions without these table variables, depending on how the membership functions are being calculated. We don’t have to perform any mathematical operations on the records returned by ordinary crisp relations, but this is not true with their fuzzy counterparts. Using a regular INTERSECT operator in the sample code in the last tutorial would have been awkward to say the least, since it would have excluded unmatched values for the MembershipScores of both sets, which must be preserved to calculate the grade for membership in the fuzzy relation. The same problem arises when we try to implement a fuzzy union with the T-SQL UNION operator, so I had to resort to a workaround similar to the one used for fuzzy intersections, with a few cosmetic changes. I use a FULL JOIN here instead of an INNER JOIN and had to add IsNull statements and a CASE to substitute grades of 0 whenever the Value of one of the columns is NULL. The same two WHERE clauses I used after the join condition in the last tutorial are present here, but are buried in two subqueries; thanks to the null checks, they’re assigned membership grades of 0 on one of the two sets, whenever the WHERE clause removes them from one side but not the other.

Figure 1: Sample Code for a Fuzzy Union on Two Different Types of Z-Scores

DECLARE @ RescalingMax decimal ( 38 , 6 ), @ RescalingMin decimal ( 38 , 6 ), @ RescalingRange decimal ( 38 , 6)

DECLARE @ ZScoreTabletable

( PrimaryKey sql_variant,

Value decimal ( 38 , 6),

ZScore decimal ( 38 , 6),

ReversedZScore as CAST ( 1 as decimal ( 38 , 6 )) ABS ( ZScore),

MembershipScore decimal ( 38 , 6),

GroupRankbigint

) DECLARE @ ModifiedZScoreTabletable

( PrimaryKey sql_variant,

Value decimal ( 38 ,本文数据库（mssql）相关术语:熊片数据库 mssql数据库 oracle数据库 pubmed数据库 access数据库 万方数据库

本文标题：Implementing Fuzzy Sets in SQL Server, Part 4: From Fuzzy Unions to Fuzzy Logic

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