SQL基础问题整理
在程序中，數據庫操作是必不可少的部分，所以我們要備足數據庫相關知識才能去應付程序中出現的種種問題。基于此，我特地在國外網站、博客上整理了一些問題，并附帶了答案和解釋、參考。為了保證“原汁原味”，我就保留了英文。大家也來看看你答對了多少？
1.SQL Server 2008 Backup
題目：Is it possible to restore a SQL Server 2008 Enterprise Edition compressed? backup to a SQL Server 2008 Standard Edition?
答案：yes
解釋：RESTORE from compressed backups on SQL Server 2008 Standard Edition is? possible, although the backup compression feature is not supported in SQL Server? 2008 Standard Edition.
參考：備份壓縮 (SQL Server)
2.Identity
題目：We want to insert record into table a
create table a (a int identity(1,1))Which statement will work?
答案：insert into a default values
解釋：An insert statement with "default values" works.
參考：INSERT
3.Dynamic SQL
題目：Sam has to run a query dynamically & get the count in a variable and do? some processing based on the count. Which of the following queries will return? expected output?
declare @tablevariable varchar(100) set @tablevariable = 'Employees'A)
declare @sql varchar(100) Declare @cnt int Set @sql = 'Select ' + Convert(varchar(100),@cnt) + ' =count(*) from ' + @tablevariable Exec (@sql) select @cntB)
declare @sql varchar(100) Declare @cnt int Set @sql = 'Select count(*) from ' + @tablevariable @cnt = Exec (@sql) select @cntC)
DECLARE @sql nvarchar(4000), @params nvarchar(4000), @count int SELECT @sql = N' SELECT @cnt = COUNT(*) FROM dbo.' + quotename(@tablevariable) SELECT @params = N'@cnt int OUTPUT' EXEC sp_executesql @sql, @params, @cnt = @count OUTPUT select @count答案：C
解釋：For getting a variable as output in a dynamic statement, we need to use? sp_executeSQL.
參考：Introducing Dynamic SQL
4.T-SQL Output Clause
題目：Executing the following code. How many rows are returned by the first and? second SELECT * FROM #CategoryChanges statements?
USE Northwind; CREATE TABLE #CategoryChanges (ChangeID int Primary Key Identity, CategoryID int, OldCategoryName nvarchar(15), NewCategoryName nvarchar(15), ModifiedDate datetime2, LoginID nvarchar(30)); BEGIN TRANSACTION UPDATE Categories SET CategoryName = 'Dried Produce' OUTPUT inserted.CategoryID, deleted.CategoryName, inserted.CategoryName, getdate(), SUSER_SNAME() INTO #CategoryChanges WHERE CategoryID = 7; SELECT * FROM #CategoryChanges --first select statement Rollback tran SELECT * FROM #CategoryChanges --second select statementChoose your answer:
答案：1st 1 row, 2nd 0 rows
解釋：The ROLLBACK TRANSACTION rolls back both the update to the table? categories and the temp table #CategoryChanges.
5.T-SQL
題目：In T-SQL, what would this be considered: " colmnnX IN (x, y, z, ...)"
答案：Predicate
解釋：In T-SQL, a PREDICATE allows you to check whether a value or scalar? expression evaluates to TRUE, FALSE, or UNKNOWN. The IN clause, with column and? values becomes a predicate and checks to see if at least one of the elements in? a set is equal to a given value or expression.
參考：謂詞 (Transact-SQL)
6.Server Administration
題目：Select the best option to allocate maximum available RAM (Already? installed on Windows) to SQL Server where system has following configuration:? OS: Windows 2008 64 bit, Enterprise Edition. SQL: SQL Server 2008 64 bit,? Enterprise Edition. RAM: 6 GB.
Choose your answer
答案：Do Nothing
解釋：AWE is valid option for 32 bit architecture. Note that the sp_configure? awe enabled option is present on 64-bit SQL Server, but it is ignored. It is? subject to removal in future releases or service packs of 64-bit SQL Server.
3 GB Switch is supported for 32 bit editions. It tell operating system to? allocate 2 GB RAM to OS and 2 GB RAM to other program such as SQL Or Exchange,? if 4 GB RAM is installed.
參考：內存體系結構
7.SQL Server 2008
題目：The DEFAULT value for a column can be specified in the definition of a? user-defined table type?
答案：True
解釋：A DEFAULT value can be specified in the definition of a user-defined table? type.
參考：CREATE? TYPE (Transact-SQL)
8.Session Settings
題目：In SQL 2008, the QOD_Customers table contains the column [Region] [nvarchar](15)? NULL and 90 rows of data. The following stored procedure is created and then? run.
SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO CREATE PROCEDURE [dbo].[QOD_Test_1] ASSET ANSI_DEFAULTS ON -- Before rollback Select StatementSELECT COUNT(CompanyName) AS 'Before rollback' FROM [dbo].[QOD_Customers]WHERE [dbo].[QOD_Customers].[Region] IS NULLUPDATE Dbo.QOD_Customers SET Region = 'XXX' WHERE dbo.QOD_Customers.region IS NULL -- The after update Select StatementSELECT COUNT(CompanyName) AS 'After update' FROM [dbo].[QOD_Customers]WHERE [dbo].[QOD_Customers].[Region] IS NULLROLLBACK TRANSACTION SET ANSI_DEFAULTS OFF -- The after rollback Select StatementSELECT COUNT(CompanyName) AS 'After Rollback' FROM [dbo].[QOD_Customers]WHERE [dbo].[QOD_Customers].[Region] IS NULL GOThe before rollback Select statement returns a count of 60. The after update? Select statement returns a count of 0 What count of rows does the after rollback? Select statement return?
答案：60
解釋：When ANSI_DEFAULTS is enabled (ON), this option enables the following ISO? settings:...SET IMPLICIT_TRANSACTIONS. Msg 3903 The ROLLBACK TRANSACTION request? has no corresponding BEGIN TRANSACTION.
參考：SET? ANSI_DEFAULTS (Transact-SQL)
9.Severity Levels
題目：Error messages with severity levels below 10 indicate what?
Choose your answer:
答案：Informational messages
解釋：This is an informational message that indicates a problem caused by? mistakes in the information the user has entered and not actual errors.
參考：Error? Message Severity Levels
10.Exec on Linked Server
題目：What parameter marker is used, when EXEC() is executed on a Linked Server?
答案：?
解釋：There is one thing that you can do with EXEC() at a linked server, that? you cannot do with EXEC() on a local server: you can use parameters, both for? input and output. The confuse matters, you don't use parameters with names? starting with @, instead you use question marks (?) as parameter holders. You? can run this:
DECLARE @cnt int EXEC('SELECT ? = COUNT(*) FROM Northwind.dbo.Orders WHERE CustomerID = ?', @cnt OUTPUT, N'VINET') AT SQL2K SELECT @cnt參考：How to use EXEC() at Linked Server
11.SQL 2005 - Table-Valued Parameters
題目：In SQL Server 2005 variables and parameters of a table type can be set to? NULL?
答案：SQL 2005 does not support Table-Valued Parameters
解釋：Only SQL Server 2008 supports the Table-Valued Parameters. This was not a? feature available in SQL Server 2005.
12.SQL Server 2008 Policy-Based Management
題目：SQL Server 2008 Policies can be defined against the following SQL Server? Editions. Choose all if apply.
Choose your answer:
答案：SQL Server 2008, SQL Server 2005, SQL Server 2000
解釋：The Enterprise Policy Management (EPM) Framework leverages and extends the? new Microsoft SQL Server 2008 Policy-Based Management feature across an entire? SQL Server enterprise, including down-level instances of SQL Server such as SQL? Server 2000 and SQL Server 2005.
參考：Enterprise? Policy Management Framework with SQL Server 2008
13.Indexes in SQL Server 2005
題目：What is the maximum number of indexes (clustered and nonclustered) allowed? for a table in SQL Server 2005?
答案：250
解釋：Number of Clustered indexes in SQL 2005 is one and 249 non clustered? indexes, altogether 250 indexes for a table in SQL Server 2005. In SQL Server? 2008, the maximum is 1000.
參考：CREATE? INDEX (Transact-SQL)
14.Predict output
題目：Try to predict the output of this code...
declare @i int, @j intset @i = 1 create table #temp (id int)while (@i<=5)beginbegin trybegin transactionif (@i = 3) set @j = @i/0insert into #temp values (@i)commit transactionend try begin catchrollback transactionprint 'this is an exception';end catchset @i = @i + 1 endselect * from #tempChoose your answer:
答案：Results: 1 2 4 5 Message: this is an exception
解釋：This is a beautiful usage of TRY-CATCH block with looping. This will do? the action, create the error message for the erroneous action, don't disturb the? other actions and iterate until the last one. The results will include 4 rows,? skipping the "3" and the Messages tab will list the exception.
15.Database Size
題目：What is the Initial size of newly created database (w/o specifiing the? size for mdf/ldf)?
答案：3MB
解釋：When you create the database without specifying the size for mdf / ldf the? initial size for the database if 3 MB. Click on the database node create new? database enter database name just click on OK. Check the size in properties or? can also see the before creating it in Initial Size col of New database dialog? box.
The default size for an mdf is 2MB and 1MB for an ldf, based on the model? database.
16.Removing permissions
題目：You have a standard SQL Server 2005 instance. You allow the user 'Mary' to? call a stored procedure 'UpdateCustomer' by using the following sql :
grant execute on UpdateCustomer to MaryPrior to issuing this statement, Mary had no explicit permissions on the SP.? You then realise that you've made a mistake and want to reverse the action you? have just taken. Which statement is the best option, without impacting on any? other effective permissions?
Choose your answer:
答案：REVOKE EXECUTE permission statement
解釋：You are simply looking to revoke the permission you have just granted.? DENY would take precedence over any other effective permissions, and may not be? what you want to achieve. REMOVE and GRANT NONEXECUTE are not valid SQL.
17.Declarative Data Integrity
題目：After executing the following code, how many rows remain in each table? (Countries, Cities and Buyers)?
CREATE TABLE Test.Countries(CountryId INT PRIMARY KEY) INSERT INTO Test.Countries VALUES(1),(2),(3) GO CREATE TABLE Test.Cities( CityId INT PRIMARY KEY,CountryId INT REFERENCES Test.Countries ON DELETE CASCADE); INSERT INTO Test.Cities VALUES(1,1),(2,1),(3,2) GO CREATE TABLE Test.Buyers(CustomerId INT PRIMARY KEY,CityId INT REFERENCES Test.Cities ON DELETE CASCADE);INSERT INTO Test.Buyers VALUES(1,1),(2,1),(3,2) GODELETE FROM Test.Countries WHERE CountryId = 1答案：Countries 2, Cities 1, Buyers 0
解釋：The constraints prevent some inserts and deletes from occurring.
參考：級聯引用完整性約束
18.Wildcard
題目：From the data below, I need to get records with the FirstName of Kim or? Tim only. Frame the query, applying a wildcard search on the FirstName column.
答案：WHERE FirstName LIKE '[KT]im'
解釋：The wildcards that can be used with LIKE include the brackets, [], which match any single character that's included inside them with the data in the field.
參考：LIKE (Transact-SQL)
19.Query cost
題目：Which of the two WHERE clauses is cost effective:
--1. SELECT [name] FROM teacher WHERE teacher_id IN (SELECT teacher_id FROM student)--2. SELECT [name] FROM teacher WHERE EXISTS (SELECT 1 FROM student WHERE teacher.teacher_id = student.teacher_id)答案：2 is more cost effective
解釋：This is not a great question, and there is some debate about it. Please? read the discussion to understand. The original explanation is below:
EXISTS will return a boolean value, while IN retruns actual result set? (making results from IN heavier than EXISTS).
參考：EXISTS (Transact-SQL)、IN (Transact-SQL)
20.Bit by bit
題目：What will be result of following query:
DECLARE @bit BIT SET @bit = 500IF @bit = 1 PRINT 'yes' ELSE PRINT 'no'答案：yes
解釋：Bit constants are represented by the numbers 0 or 1, if a number larger? than one is used, it is converted to one.
參考：常量(Transact-SQL)
21.Rowcount
題目：In SQL Server 2005/2008, what would be the output of this code when you? open a new query window and execute it?
select @@ROWCOUNT select @@ROWCOUNT答案：1,1
解釋：When we first open a query window, the client must execute something to? connect with no results. However the result of @@rowcount is set to one. If you? were to execute some command like a SET NOCOUNT ON will @@rowcount return 0.
轉載于:https://www.cnblogs.com/jameslif/p/3620907.html
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