MySQL MySQL局部变量
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MySQL local variables
提问by CodeKingPlusPlus
I am trying to define and initialize a MySQL variable for a query.
我正在尝试为查询定义和初始化 MySQL 变量。
I have the following:
我有以下几点：
declare @countTotal int;
SET @countTotal = select COUNT(*)
from nGrams;
I am using MySQL in Netbeans and it tells me I have an error. What/where is my error?
我在 Netbeans 中使用 MySQL，它告诉我我有一个错误。我的错误是什么/在哪里？
How can I fix this?
我怎样才能解决这个问题？
回答by eggyal
MySQL has two different types of variable:
MySQL 有两种不同类型的变量：
local variables(which are notprefixed by
@) are strongly typed and scoped to the stored program block in which they are declared. Note that, as documented underDECLARESyntax:DECLAREis permitted only inside aBEGIN ... ENDcompound statement and must be at its start, before any other statements.user variables(which areprefixed by
@) are loosely typed and scoped to the session. Note that they neither need nor can be declared—just use them directly.
局部变量（不以 为前缀
@）是强类型的，其作用域限定在声明它们的存储程序块内。请注意，如DECLARESyntax下所述：DECLARE只允许在BEGIN ... END复合语句中，并且必须在它的开头，在任何其他语句之前。用户变量（以为前缀
@）是松散类型的并且作用域为会话。请注意，它们既不需要也不能声明——只需直接使用它们即可。
Therefore, if you are defining a stored program and actually do want a "local variable", per the wording in your question, you will need to drop the @character and ensure that your DECLAREstatement is at the start of your program block. Otherwise, to use a "user variable", drop the DECLAREstatement.
因此，如果您正在定义一个存储程序并且实际上确实需要一个“局部变量”，根据您问题中的措辞，您将需要删除该@字符并确保您的DECLARE语句位于程序块的开头。否则，要使用“用户变量”，请删除该DECLARE语句。
Furthermore, you will either need to surround your query in parentheses in order to execute it as a subquery:
此外，您需要将查询括在括号中，以便将其作为子查询执行：
SET @countTotal = (SELECT COUNT(*) FROM nGrams);
Or else, you could use SELECT ... INTO:
否则，您可以使用SELECT ... INTO：
SELECT COUNT(*) INTO @countTotal FROM nGrams;
回答by Rahul Tripathi
Try this:-
尝试这个：-
select @countTotal := COUNT(*) from nGrams;
回答by alditis
Function example:
功能示例：
DROP FUNCTION IF EXISTS test;
DELIMITER $$
CREATE FUNCTION test(in_number INT) RETURNS INT
BEGIN
DECLARE countTotal INT;
SET countTotal = SELECT COUNT(*) FROM nGrams;
RETURN countTotal + in_number;
END $$
DELIMITER ;
回答by Olaf Dietsche
According to DECLARE Syntax, declaremust be inside a begin...end block.
根据DECLARE Syntax，declare必须在 begin...end 块内。
