mysql - 如何为 MySQL 中的字段或列设置别名？

Question

我正在尝试做这样的事情。但我得到一个未知的列错误:

SELECT SUM(field1 + field2) AS col1, col1 + field3 AS col3 from core

基本上，我只想使用别名，这样我就不需要执行之前执行的操作。这在mysql中可以吗？

Answer 1

select @code:= SUM(field1 + field2), @code+1 from abc;

但是，请注意以下事项(来自 MySQL 5.6 docs):

As a general rule, other than in SET statements, you should never assign a value to a user variable and read the value within the same statement. For example, to increment a variable, this is okay:

SET @a = @a + 1;

For other statements, such as SELECT, you might get the results you expect, but this is not guaranteed. In the following statement, you might think that MySQL will evaluate @a first and then do an assignment second:

SELECT @a, @a:=@a+1, ...;

However, the order of evaluation for expressions involving user variables is undefined.

因此，使用风险自负。