一道sql面试题附答案

有1张表, Wages表 ——————————————-
Emp_id|基本工资|工龄工资| ——————————————-
1|1.00|1.00| ——————————————- 2|1.00|2.00|
——————————————- 3|1.00|3.00|
——————————————- 4|1.00|4.00|
——————————————- ………

1. TVP, 表变量,临时表,CTE 的区别
TVP和临时表都是可以索引的,总是存在tempdb中,会增加系统数据库开销,而表变量和CTE只有在内存溢出时才会被写入tempdb中。对于数据量大,并且反复使用,反复进行查询关联的,建议使用临时表或TVP,数据量小,使用表变量或CTE比较合适

CTE 也叫公用表表达式和派生表非常类似 先定义一个USACusts的CTE  

请从上表用“一句组合查询”查询出工资统计表,要求检索出的内容格式如下:

  1. sql_variant 万能类型
    可以存放所有数据类型,相当于C#中的object数据类型 3. datetime,
    datetime2, datetimeoffset datetime 时间有效期较小,在1753-1-1
    之前就不能使用了,精度为毫秒级别,而datetime2
    数据范围相当于C#中的datetime
    ,精度达到了秒后面小数点后7位,datetimeoffset则是考虑是时区的日期类型 4.
    MERGE的用法
    语法很简单就不说了,主要是处理两张表某些字段对比后的操作,需注意 when
    not matched (by target) 与 when not matched by
    source的区别,前者是是针对对比后目标表不存在的记录,可以选择insert操作,而后者则是针对对比后目标表多出来的记录,可以选择delete或update操作
  2. rowversion 类型
    代替以前的timestamp,时间戳,8字节二进制值,常用来进行解决并发操作的问题
  3. Sysdatetime() 返回datetime2类型,精度比datetime高 7. with cube , with
    rollup , grouping sets 运算符 都可与group by 后连用,with cube
    表示汇总所有级别的组合,with rollup
    则是按级别汇总,从下面的代码可以详细看出区别。注意,汇总行,null可以看成所有值
    而grouping sets运算符,则仅返回每个分组顶级汇总行,在查询汇总行中
    可使用grouping(字段名) = 1来判断,该运算符可和rollup,
    cube连用,表示按照grouping by sets和按照rollup/cube处理的结果集union all
    示例代码如下: 复制代码 代码如下: With
    cube, With rollup –示例代码 declare @t table(goodsname VARCHAR(max)
    ,sku1name VARCHAR(max) , sku2name VARCHAR(max), qty INT) insert @t
    select ‘凡客TX’,’红色’,’S’,1 insert @t select ‘凡客TX’,’黑色’,’S’,2
    insert @t select ‘凡客TX’,’白色’,’L’,3 insert @t select
    ‘京东村山’,’白色’,’L’,4 insert @t select ‘京东村山’,’红色’,’S’,5 insert
    @t select ‘京东村山’,’黑色’,’L’,6 insert @t select
    ‘亚马逊拖鞋’,’白色’,’L’,7 insert @t select ‘亚马逊拖鞋’,’红色’,’S’,8
    SELECT * FROM @t select goodsname,sku1name,sku2name,sum(qty) sumqty
    from @t group by goodsname,sku1name,sku2name with rollup ORDER BY
    goodsname,sku1name,sku2name select goodsname,sku1name,sku2name,sum(qty)
    sumqty from @t group by goodsname,sku1name,sku2name with cube ORDER BY
    goodsname,sku1name,sku2name ———————– declare @t
    table(goodsname VARCHAR(max) ,sku1name VARCHAR(max) , sku2name
    VARCHAR(max), qty INT) insert @t select ‘凡客TX’,’红色’,’S’,1 insert @t
    select ‘凡客TX’,’黑色’,’S’,2 insert @t select ‘凡客TX’,’白色’,’L’,3
    insert @t select ‘京东村山’,’白色’,’L’,4 insert @t select
    ‘京东村山’,’红色’,’S’,5 insert @t select ‘京东村山’,’黑色’,’L’,6 insert
    @t select ‘亚马逊拖鞋’,’白色’,’L’,7 insert @t select
    ‘亚马逊拖鞋’,’红色’,’S’,8 –GROUPING SETS 运算符 SELECT
    goodsname,sku1name,sku2name, SUM(qty) FROM @t GROUP BY GROUPING
    SETS(goodsname,sku1name,sku2name) SELECT goodsname, sku1name, sku2name
    ,SUM(qty) FROM @t GROUP BY GROUPING SETS(goodsname),
    ROLLUP(sku1name,sku2name) ORDER BY goodsname,sku1name,sku2name SELECT
    goodsname, sku1name, sku2name ,SUM(qty) FROM @t GROUP BY
    ROLLUP(goodsname,sku1name,sku2name) ORDER BY goodsname,sku1name,sku2name
    SELECT CASE WHEN GROUPING(goodsname) = 1 THEN ‘[ALL]’ ELSE goodsname
    END goodsname, CASE WHEN GROUPING(sku1name) = 1 THEN ‘[ALL]’ ELSE
    sku1name END sku1name, CASE WHEN GROUPING(sku2name) = 1 THEN ‘[ALL]’
    ELSE sku2name END sku2name ,SUM(qty) FROM @t GROUP BY GROUPING
    SETS(goodsname), ROLLUP(sku1name,sku2name) ORDER BY
    goodsname,sku1name,sku2name 8. 一些快捷的语法 例如 Declare @id int = 0
    虽然有时很快捷,但DBA不建议这样使用,Declare @id = select top 1 id from
    表名,建议声明和查表赋值分开 9. 公用表达式 CTE
    特点:可嵌套使用,代替联接表中的子查询,结构层次更加清晰,也可用来递归查询,另外通过巧妙的常量列控制递归层次
    示例代码如下: 复制代码 代码如下:
    –公用表达式CTE Common table expression –用CTE实现递归算法 CREATE TABLE
    EMPLOYEETREE( EMPLOYEE INT PRIMARY KEY, employeename nvarchar(50),
    reportsto int ) insert into EMPLOYEETREE values(1,’Richard’,null) insert
    into EMPLOYEETREE values(2,’Stephen’,1) insert into EMPLOYEETREE
    values(3,’Clemens’,2) insert into EMPLOYEETREE values(4,’Malek’,2)
    insert into EMPLOYEETREE values(5,’Goksin’,4) insert into EMPLOYEETREE
    values(6,’Kimberly’,1) insert into EMPLOYEETREE values(7,’Ramesh’,5)
    ———————- –确定哪些员工向Stephen报告的递归查询 with
    employeeTemp as ( select EMPLOYEE, employeename, reportsto from
    EMPLOYEETREE where EMPLOYEE = 2 union all select a.EMPLOYEE,
    a.employeename, a.reportsto from EMPLOYEETREE as a inner join
    employeeTemp as b on a.reportsto = b.EMPLOYEE ) select * from
    employeeTemp where EMPLOYEE 2 –option(maxrecursion 2)
    –不报错设置级联关联递归 with employeeTemp as ( select EMPLOYEE,
    employeename, reportsto,0 as sublevel from EMPLOYEETREE where EMPLOYEE =
    2 union all select a.EMPLOYEE, a.employeename, a.reportsto,sublevel+1
    from EMPLOYEETREE as a inner join employeeTemp as b on a.reportsto =
    b.EMPLOYEE ) select * from employeeTemp where EMPLOYEE 2 and sublevel
    =2 –option(maxrecursion 2) 10. pivot 与 unpivot
    前者用在行转列,注意:必须用聚合函数与PIVOT一起使用,计算聚会时将不考虑出现在值列中的任何空值;一般情况下,可以用列上的子查询来替换pivot语句,但是这样做效率不高
    后者用在列转行,注意:如果某些列中有null值,将会被过滤掉,不产生新行;语法上For前指定的新列,对应原表指定列名中的值,For后指定的新列对应原表指定列名中的标题的值
    两者都有的共性:语法上最后必须要有别名;IN里面指定的列类型必须是一致的。
    示例代码如下: 复制代码 代码如下:
    pivot与unpivot –关于PIVOT的操作 CREATE TABLE #test ( NAME
    VARCHAR(max), SCORE INT ) INSERT INTO #test VALUES (‘张三’,’97’) INSERT
    INTO #test VALUES (‘李四’,’28’) INSERT INTO #test VALUES (‘王五’,’33’)
    INSERT INTO #test VALUES (‘神人’,’78’) –NAME SCORE –张三 97 –李四 28
    –王五 33 –神人 78 –行转列 SELECT –‘成绩单’ AS SCORENAME , [张三],
    [李四], [王五] FROM #test PIVOT (AVG(SCORE) FOR NAME IN ([张三],
    [李四], [王五])) b —————————————– CREATE
    TABLE VendorEmployee( VendorId INT, Emp1Order INT, Emp2Order INT,
    Emp3Order INT, Emp4Order INT, Emp5Order INT, ) GO INSERT INTO
    VendorEmployee VALUES(1,4,3,5,4,4) INSERT INTO VendorEmployee
    VALUES(2,4,1,5,5,5) INSERT INTO VendorEmployee VALUES(3,4,3,5,4,4)
    INSERT INTO VendorEmployee VALUES(4,4,2,5,4,4) INSERT INTO
    VendorEmployee VALUES(5,5,1,5,5,5) SELECT * FROM VendorEmployee
    —————- –列转行 SELECT * FROM ( SELECT
    VendorId,[Emp1Order],[Emp2Order],[Emp3Order],[Emp4Order],[Emp5Order]
    FROM VendorEmployee) AS unpiv UNPIVOT (orders FOR elyid IN
    ([Emp1Order],[Emp2Order],[Emp3Order],[Emp4Order],[Emp5Order]))
    AS child ORDER BY elyid SELECT * FROM VendorEmployee UNPIVOT (orders
    FOR elyid IN
    ([Emp1Order],[Emp2Order],[Emp3Order],[Emp4Order],[Emp5Order]))
    AS child ORDER BY elyid SELECT * FROM VendorEmployee UNPIVOT ( ORDERS
    FOR [操作员名字] IN
    ([Emp1Order],[Emp2Order],[Emp3Order],[Emp4Order],[Emp5Order]))
WITH USACusts AS
(
  SELECT custid, companyname
  FROM Sales.Customers
  WHERE country = N'USA'
)
SELECT * FROM USACusts;

Emp_id|基本工资|工龄工资|合计|名次

with  ()  称为内部查询 
 与派生表相同,一旦外部查询完成后,CTE就自动释放了

1|1.00|1.00|2.00|x

CTE内部方式 就是上面代码所表示的方式  其实还有一种外部方式

2|1.00|2.00|3.00|y

WITH C(orderyear, custid) AS
(
  SELECT YEAR(orderdate), custid
  FROM Sales.Orders
)
SELECT orderyear, COUNT(DISTINCT custid) AS numcusts
FROM C
GROUP BY orderyear;
GO

C(orderyear, custid)  可以理解为 select orderyear, custid from C   指定返回你想要的列  不过个人感觉没什么用!

它和派生表相同 也可以在CTE中查询使用参数

DECLARE @empid AS INT = 3;

WITH C AS
(
  SELECT YEAR(orderdate) AS orderyear, custid
  FROM Sales.Orders
  WHERE empid = @empid
)
SELECT orderyear, COUNT(DISTINCT custid) AS numcusts
FROM C
GROUP BY orderyear;
GO

3|1.00|3.00|4.00|..

定义多个CTE

4|1.00|4.00|5.00|..

回答: 复制代码 代码如下:begintran
createtableWages(Emp_idbigintnotnullprimarykey,基本工资money,工龄工资money)
go insertintoWages(Emp_id,基本工资,工龄工资)values(1,1.00,1.00)
insertintoWages(Emp_id,基本工资,工龄工资)values(2,1.00,2.00)
insertintoWages(Emp_id,基本工资,工龄工资)values(3,1.00,3.00)
insertintoWages(Emp_id,基本工资,工龄工资)values(4,1.00,4.00)
if@@error0rollbackelsecommittran
selectEmp_id,基本工资,工龄工资,基本工资+工龄工资as合计,row_number()over(orderby基本工资+工龄工资)as名次fromWagesorderby合计
–droptableWages

WITH C1 AS
(
  SELECT YEAR(orderdate) AS orderyear, custid
  FROM Sales.Orders
),
C2 AS
(
  SELECT orderyear, COUNT(DISTINCT custid) AS numcusts
  FROM C1
  GROUP BY orderyear
)
SELECT orderyear, numcusts
FROM C2
WHERE numcusts > 70;

多个CTE用 , 隔开 通过with 内存 可以在外查询中多次引用