Question

这段代码不起作用：

DECLARE @CollationName varchar(50)
set @CollationName = (
    select collation_name
    from information_schema.columns
    where table_name = 'MeteringPointPrice' and column_name = 'MeteringPointId'
)

if OBJECT_ID('tempdb..#MPLIST2') IS NOT NULL
    drop table #MPLIST2
if @CollationName = 'SQL_Danish_Pref_CP1_CI_AS'
    create table #MPLIST2 (MeteringPointId varchar(18) COLLATE SQL_Danish_Pref_CP1_CI_AS)
if @CollationName = 'Danish_Norwegian_CI_AS'
    create table #MPLIST2(MeteringPointId varchar(18) COLLATE Danish_Norwegian_CI_AS)

select @CollationName gives: Danish_Norwegian_CI_AS

但是两个if语句都运行所以临时表＃MPLIST2创建了2次，这当然会产生错误。

我无法弄清楚原因。

以下代码有所改变：

DECLARE @CollationName varchar(50)
set @CollationName = (
    select collation_name
    from information_schema.columns
    where table_name = 'MeteringPointPrice' and column_name = 'MeteringPointId'
)


if OBJECT_ID('tempdb..#MPLIST2') IS NOT NULL
    drop table #MPLIST2

if @CollationName = 'Danish_Norwegian_CI_AS'
    begin
        create table #MPLIST2 (MeteringPointId varchar(18) COLLATE Danish_Norwegian_CI_AS)
    end

if OBJECT_ID('tempdb..#MPLIST2') IS NULL
    begin
        select 'hellooo'
        --create table #MPLIST2 (MeteringPointId varchar(18) COLLATE SQL_Danish_Pref_CP1_CI_AS)
    end

这部分成功执行，没有＆＃39; hellooo＆＃39;。但是，如果我在＆＃34;创建表格中评论＆＃39;在下面一行，然后它给出了错误＆＃34;已经有一个名为＆＃39;＃MPLIST2＆＃39;在数据库中。＆＃34;

Answer 1

出现问题是因为整个语句是同时编译的。因此，创建现有表（例如）的条件会导致错误。一种解决方案是动态SQL，但这很麻烦。另一个是简单地使用GO：

DECLARE @CollationName varchar(50)
set @CollationName = (
    select collation_name
    from information_schema.columns
    where table_name = 'MeteringPointPrice' and column_name = 'MeteringPointId'
)
GO

if OBJECT_ID('tempdb..#MPLIST2') IS NOT NULL
    drop table #MPLIST2
GO

if @CollationName = 'Danish_Norwegian_CI_AS'
    begin
        create table #MPLIST2 (MeteringPointId varchar(18) COLLATE Danish_Norwegian_CI_AS)
    end;
GO

if OBJECT_ID('tempdb..#MPLIST2') IS NULL
    begin
        select 'hellooo'
        --create table #MPLIST2 (MeteringPointId varchar(18) COLLATE SQL_Danish_Pref_CP1_CI_AS)
    end
GO

这会在脚本中生成单独的事务批处理，从而防止出错。

简单if语句不起作用（字符串比较）

1 个答案: