SQL Server – 我常用语句

前言

旧没用又忘记了, 又没有 intellisense, 记入这里吧.

Reset Auto Increment

DBCC CHECKIDENT ('TableName'); -- check current
DBCC CHECKIDENT ('TableName', RESEED, 0); -- reset to 0, next is 1

On/Off Auto Increment

Set Identity_Insert [TableName] Off;
Set Identity_Insert [TableName] On; 

很神奇.. On 的时候 insert 需要 Id, Off 反而不需要 Id...这不是反了吗?

官网的解释: Allows explicit values to be inserted into the identity column of a table, On 就是 allow 插入 Id

Int to String with Leading Zero

SELECT FORMAT(1, 'd2') --01

d2 就 2 位数, 3 就 3位数, 以此类推

Declare and Set Value

go
    declare @value nvarchar(max) = N'dada';
    set @value = N'super';
    -- select @value = count(*) from @table;
    print @value;
go

If Else

go
    declare @value2 nvarchar(30) = 'keatkeat2';
    if(@value2 = 'keatkeat')
        begin
            print 'yes';
        end
    else
        begin
            print 'no';
        end
go

Ternary Operator

declare @value nvarchar(max) = IIF(1, 'yes', 'no');

For Loop

go
    declare @i int = 0;
    while(@i < 10)
    begin
        print @i;
        set @i = @i + 1;
    end
go

Random String and Number

go

     SELECT CONVERT(INT, 5 * RAND())
     SELECT SUBSTRING(CONVERT(varchar(255), NEWID()), 0, 9)
     select NEWID();
go

Random Data for Test Performance

create table

CREATE TABLE [dbo].[Test] (
    [Id] int NOT NULL IDENTITY,
    [FirstName] nvarchar(450) NOT NULL DEFAULT '',
    [LastName] nvarchar(450) NOT NULL DEFAULT '',
    [Nickname] nvarchar(450) NOT NULL DEFAULT '',
    [Age] int NOT NULL DEFAULT 0,
    CONSTRAINT [PK_Test] PRIMARY KEY CLUSTERED ([Id] ASC)
);

loop insert data

go
declare @index int = 0;
declare @length int = 1000000;

while (@index < @length)
begin
    insert into Test
    ([FirstName], [LastName], [Nickname], [Age])
    values
    (
        SUBSTRING(CONVERT(varchar(255), NEWID()), 0, 9),
        SUBSTRING(CONVERT(varchar(255), NEWID()), 0, 9),
        SUBSTRING(CONVERT(varchar(255), NEWID()), 0, 9),
        CONVERT(INT, 200 * RAND())
    );
  set @index = @index + 1;
end
go

batch insert data

insert into Test ([FirstName], [LastName], [Nickname], [Age]) select
    SUBSTRING(CONVERT(varchar(255), NEWID()), 0, 9),
    SUBSTRING(CONVERT(varchar(255), NEWID()), 0, 9),
    SUBSTRING(CONVERT(varchar(255), NEWID()), 0, 9),
    CONVERT(INT, 200 * RAND())
from Test;

Create Variable Table and Loop

-- create temp table and loop it
go
    declare @temp table (name nvarchar(max), [index] int identity(1,1));
    insert into @temp (name) values ('keatkeat'), ('xinyao');

    declare @i int = 0;
    declare @length int;
    select @length = count(*) from @temp;
    while(@i < @length)
    begin
        declare @value nvarchar(max)
        select @value = name from @temp order by [index] offset @i rows fetch next 1 rows only;
        print @value;
        set @i = @i + 1;
    end
go

Select into + row number

select value, ROW_NUMBER() over(order by (select null)) as [RowNumber] from STRING_SPLIT('a,b,c', ',');

String Contains

declare @value nvarchar(max) = IIF('value' like '%lu%', 'yes', 'no');
--关键 'value' like '%lu%'

Date Format

参考: Stack Overflow – How to display the date as mm/dd/yyyy hh:mm Am/PM using sql server 2008 r2?

select FORMAT(cast('2022-12-01 09:07:02.805 +08:00' as datetimeoffset), 'MM/dd/yyyy hh:mm:s tt');

Date Adjustment

select CreatedDate, ValidHour, DATEADD(HOUR, ValidHour, CreatedDate) as ValidUntil from voucher;

Try Catch Throw

begin try
    throw 50000, 'custom error',1;
end try
begin catch
    print(ERROR_MESSAGE()); -- custom error.
    print(ERROR_SEVERITY()); -- 16
    print(ERROR_STATE()); -- 1
end catch

注: 在 if statment 里面 throw 要加分号 ; 哦. 参考: Stack Overflow – SQL only a throw inside if statement

Get First Row After Group By (use CTE)

with cte as
(
    select FORMAT(DateCreated, 'dd-MMM hh:mm tt') as [Date], DateCreated, CustomerName, CustomerContact, CustomerEnquiry, CustomerAction, GoogleClickId,
    ROW_NUMBER() over (partition by CustomerName, CustomerContact order by DateCreated desc) as RowNumber
    from Conversion
    where DateCreated >= '2023-02-17' and CustomerContact not like '%test%'
)
select [Date], CustomerName, CustomerContact, CustomerEnquiry, CustomerAction, GoogleClickId
from cte where RowNumber = 1 order by DateCreated desc;

Group by 后那每个 group 的第一条数据

Get All Table Column Name

SELECT STRING_AGG ('['+ COLUMN_NAME +']', ', ') AS [COLUMNS]
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = N'AccountsReceivable';

without computed column

select STRING_AGG ('['+ COLUMN_NAME +']', ', ') AS [COLUMNS]
from INFORMATION_SCHEMA.COLUMNS ColumnTable
left join sys.computed_columns ComputedColumnTable on
OBJECT_NAME(ComputedColumnTable.object_id) = ColumnTable.TABLE_NAME and ComputedColumnTable.[name] = ColumnTable.COLUMN_NAME
WHERE ComputedColumnTable.object_id is null and ColumnTable.TABLE_NAME = 'AccountsReceivable';

Testing Performance

DBCC DROPCLEANBUFFERS --清空执行计划缓存
DBCC FREEPROCCACHE --清空数据缓存
SET STATISTICS IO ON;
SET STATISTICS TIME ON;

left join TestChild WITH (INDEX([IX_TestChild_TestId])) --强制使用 index

-- 强制 join pattern
left hash join
left merge join
left loop join

Disable Index and Constraints

alter index [IX_IndexName] on [TableName] disable;
alter index [IX_IndexName] on [TableName] rebuild;