sql - 如何在查询（SQL Server）中使用 SQL 变量？

Question

我编写了以下 SQL 存储过程，它一直在给我错误 @pid = SELECT MAX(...整个过程是：

Alter PROCEDURE insert_partyco
@pname varchar(200)
AS
BEGIN
    DECLARE @pid varchar(200);

    @pid = SELECT MAX(party_id)+1 FROM PARTY;
    INSERT INTO party(party_id, name) VALUES(@pid, @pname)
    SELECT SCOPE_IDENTITY() as PARTY_ID
END
GO

谁能告诉我我在这里做错了什么？

Answer 1

Alter PROCEDURE insert_partyco
@pname varchar(200)
AS
BEGIN
    DECLARE @pid varchar(200);

    SELECT @pid = MAX(party_id)+1 FROM PARTY;
    INSERT INTO party(party_id, name) VALUES(@pid, @pname)
    SELECT SCOPE_IDENTITY() as PARTY_ID
END

SET与 with相比，这有一个优势SELECT，您可以在一个语句中选择多个变量中的表达式：

SELECT @var1 = exp1, @var2 = expr2 ... etc

Answer 2

declare @total int

select @total = count(*) from news;

select * from news where newsid = @total+2

//**news** table name and **newsid** column name

Answer 3

您需要使用 SET。

Alter PROCEDURE insert_partyco
@pname varchar(200)
AS
BEGIN
    DECLARE @pid varchar(200);

    SET @pid = (SELECT MAX(party_id)+1 FROM PARTY);
    INSERT INTO party(party_id, name) VALUES(@pid, @pname)
    SELECT SCOPE_IDENTITY() as PARTY_ID
END
GO

或者，在您的情况下，您可以将 party_id 设为自动递增值，因此您无需查询表。