SQL CASE：WHEN语句的顺序是否重要？(SQL CASE: Does the order of the WHEN statements matter?)

 我使用PHP生成需要以自定义方式排序的SQL查询。 我正在生成一个CASE块，其中包含许多WHEN语句，用于指定数字排名。 包含的WHEN语句取决于我可用于查询的信息量。 例如，如果我有可用的电话，我将生成三个WHEN语句： 
 
 WHEN phone = '(202) 555-5555' AND last_name = 'Smith' and first_name = 'John' THEN 1 
 
 WHEN phone = '(202) 555-5555' AND last_name = 'Smith' THEN 2 
 
 WHEN phone = '(202) 555-5555' THEN 3 
 
 所以我根据匹配的接近程度进行排名，并且我对参数的评估是相同的（电话，名字和姓氏上的匹配应该在与地址，名字和姓氏匹配的同一层上排名）。 但是，在为多条信息（电话，地址等）生成这些语句后，我的WHEN语句将全部乱序; THEN 1终止条款将彼此分开，对于THEN 2相同，依此类推。 我可以把它们整理好，但这会让我的PHP更加冗长和丑陋。 
 
 TL; DR？ 
 
 所以简短的问题是： CASE语句中WHEN语句的顺序是否重要？ SQL（我使用的是Oracle）是第一次匹配还是评估所有可能性并分配最高排名？ 

I am using PHP to generate a SQL query that needs to be ordered in a custom way. I am generating a CASE block with a number of WHEN statements that assign a number ranking. The WHEN statements that are included are contingent on how much information I have available for querying. For example, if I have a phone available, I will generate three WHEN statements:
 
WHEN phone = '(202) 555-5555' AND last_name = 'Smith' and first_name = 'John' THEN 1
 
WHEN phone = '(202) 555-5555' AND last_name = 'Smith' THEN 2
 
WHEN phone = '(202) 555-5555' THEN 3
 
So I am ranking based on how close the match is, and I am valuing the parameters the same (a match on phone, first name, and last name should be ranked on the same tier as a match on address, first name and last name). However, after generating these statements for multiple pieces of information (phone, address, etc), my WHEN statements will be all out of order; the THEN 1 terminated clauses will be separated from each other, same for THEN 2 and so on. I could put them in order, but that would make my PHP more verbose and ugly.
 
TL;DR?
 
So the short question is: Does the order of the WHEN statements in a CASE statement matter? Does SQL (I'm using Oracle) go with the first match or does it evaluate all of the possibilities and assign the highest ranking?

原文：https://stackoverflow.com/questions/22640981