SQL server database (function 2)

function

Part I: Functions 1

• Aggregate function
• sum()
  sum, accumulate and sum the data in the specified field, and can only perform statistics on numeric fields.
• avg()
  calculates the average value and counts the average value in the specified field.
• max()
  Maximum value, count the maximum value in the specified field, if there are the same values, the first one will be displayed in physical order.
• min()The
  minimum value, which counts the minimum value in the specified field.
• count()
  find the number, count the number of data records in the specified field or in the results that meet the query conditions
• Examples:
• Query the number of employees with more than 10 years of service

select dang_an.name, count(gl) as 人数 from dang_an where gl>10 group by dang_an.name

• Query the number of male and female employees

select dang_an.sex,count(dang_an.sex)  as 人数 from dang_an   group by  sex

• Query the average salary and average assessment score of each employee

select dang_an.name,avg(gongzi.gongzi)as 平均工资,avg(kaohe.kaohe)as 平均考核分 from dang_an,gongzi,kaohe group by dang_an.name

• Query the total salary and total performance of each employee in the sales department

select dang_an.name,sum(gongzi.gongzi)as 总工资,sum(yeji.yeji)as 总业绩 from dang_an,zhiwei,gongzi,yeji where dang_an.zw_id=zhiwei.zw_id and dang_an.id=gongzi.id and dang_an.id=yeji.id and gongzi.nian=yeji.nian and gongzi.yue=yeji.yue and zhiwei.zw='销售' group by dang_an.name

• Query all wages, maximum wages and minimum wages of each employee, displayed in the following form: name, highest, lowest

select dang_an.name as 姓名,max(gongzi.gongzi)as 最高,min(gongzi.gongzi)as 最低 from dang_an,gongzi where dang_an.id=gongzi.id group by dang_an.name

• Date function
• GetDate() Get the current system date

SELECT GETDATE()
返回：当前日期和时间

• DateAdd() Add the specified year (yy), month (mm) or day (dd)

SELECT DATEADD(mm,4,'2017-12-20')
返回：2018-04-20（增加4个月）

• DateDiff() compares the difference of the specified date part between two dates

SELECT DATEDIFF(yy,'2000-12-20','2017-06-16')
返回：17（相差17年）

• DateName() displays a string of a specific part of the specified date

SELECT DATENAME(DW,'2017-06-16')
返回：星期五（dw是星期）

• DatePart() displays the integer form of the specified date part in the date

SELECT DATEPART(mm,'2017-06-16')
返回：6（六月）

• Small expansion
• Query how many days you have lived
  select DATEDIFF(dd,'xxxx-xx-xx',GETDATE())
• Query the day of the week when each employee was born

select dang_an.name, DATENAME(dw,dang_an.csny)from dang_an