多条件统计,sql语句如何写呢?

qq_39528261 2018-02-01 08:49:18
1 2 规格 6 工作站 8 9 11 12 数量
T(L)-54 S0C0 AA1 13 A IN 11 3600
T(L)-54 S0C0 AA1 13 A IN 11 21656
T(L)-54 S0C0 AA1 13 B IN 11 3550
T(L)-54 S0J0 AA1 13 B IN 11 3550
T(L)-66 SPX0 AA1 13 B OUT 11 852
T(L)-66 S0J0 AA1 13 B IN 11 3500
T(L)-66 S0Y4 AA1 13 B IN 11 13500
T(L)-66 S0Y4 AA1 13 B IN 11 1540
T(L)-66 S0Y4 AA1 13 B IN 11 3450
T(L)-66 S0Y4 AA2 13 B IN 11 3450
T(L)-66 S0Y4 AA2 13 B IN 11 207
T(L)-66 S0Y4 AA2 13 A IN 11 3400
T-54 S000 AA2 13 A IN 8 1156
T-54 S000 AA2 13 A IN 8 540
T-54 SP00 AA2 13 A IN 8 1080
T-54 S000 AA2 13 B IN 8 640
T-54 SP00 AA2 13 A IN 8 18000
T-54 S000 AA2 13 B IN 8 480
T-54 S00Z AA1 13 A IN 8 3450
T-54 S00Z AA1 13 A IN 8 690
T-54 S00Z AA1 13 A IN 8 3400
T-54 S00Z AA7 13 A IN 8 1020
T-54 S00Z AA7 13 A IN 8 3350
T-66 S0F0 AA7 13 A OUT 8 938
T-66 SPF0 AA7 13 A OUT 8 3300
T-66 SPF0 AA7 13 A OUT 8 264
T-66 S0F0 AA1 13 B OUT 8 2340
T-66 SPF0 AA7 13 B OUT 8 3600
T(L)-66 8SCT AA1 13 A IN 11 1224
T(L)-66 8SCT AA1 13 A IN 11 3550
T(L)-66 8SCT AA1 13 B IN 11 3550
T(L)-66 8SCT AA1 13 A IN 11 1917
T-66 C AA1 13 A OUT 8 3500
T-66 C AA1 13 A OUT 8 1330
T-66 C AA1 13 B OUT 8 3450
T-66 C AA1 13 B OUT 8 2346
T-86 D AA1 13 B OUT 8 3400
T-86 D AA1 13 A OUT 8 136
T-54 FTP- AA1 13 A OUT 11 3283
T(L)-66 FTP- AA1 13 A OUT 11 1848
T(L)-66 FTP- AA1 13 A OUT 11 216
T(L)-66 FTP- AA1 13 A OUT 11 3550
T(L)-66 FTP- AA1 13 A OUT 11 3550
T-66 FTP- AA1 13 A OUT 8 1917
T-66 FTP- AA1 13 B OUT 8 3550
T(L)-66 SPX0 AA9 13 B OUT 11 3500
T(L)-66 SPX0 AA9 13 B OUT 11 3500
T(L)-66 S0J0 AA9 13 A IN 11 1330
T(L)-66 SPX0 AA9 13 A OUT 11 3450
T(L)-66 SPX0 AA9 13 A OUT 11 2760
T(L)-66 S0Y4 AA9 13 A IN 11 3400
T-54 S000 AA9 13 A IN 8 1876
T-54 SP00 AA9 13 B IN 8 3500
T-54 S000 AA9 13 B IN 8 576
T-54 SP00 AA9 13 B IN 8 720
T-54 SP00 AA9 13 B IN 8 720
T-54 S000 AA9 13 B IN 8 12244
T-54 S000 AA9 13 B IN 8 12094
T-54 S00Z AA9 13 B IN 8 22551
T-54 S00Z AA9 13 B IN 8 12227
T-54 S00Z AA9 13 A IN 8 600
T-54 S00Z AA9 13 A IN 8 180
T-66 SPF0 AA9 13 A OUT 8 180
T-66 SPF0 AA9 13 A OUT 8 180
T-66 SPF0 AA9 13 A OUT 8 360
T-66 SPF0 AA9 13 B OUT 8 480
T(L)-66 FSCG AA9 13 A OUT 11 756
T(L)-66 FSCT AA9 13 B OUT 11 160
T-54 C AA9 13 A OUT 8 160
T-86 D AA9 13 A OUT 8 2736
T(L)-54 FTP- AA9 13 B OUT 11 3550
T(L)-54 FTP- AA9 13 B OUT 11 2769
T(L)-54 FTP- AA9 13 B OUT 11 3500
T-54 YSP- AA9 13 B IN 8 3430
T-54 YSP- AA9 13 B IN 8 13450
T-54 YSP- AA9 13 A IN 8 1311
T-54 YSP- AA9 13 A IN 8 3332
T-66 FTP- AA9 13 A OUT 8 2680
T-66 FTP- AA9 13 A OUT 8 1914
T-66 FTP- AA9 13 A OUT 8 2015
T-66 FTP- AA9 13 A OUT 8 3168
T-66 FTP- AA9 13 B OUT 8 3479
T-66 C AB5 13 A OUT 8 3266
T-66 C AB5 13 B OUT 8 3500
T(L)-66 FTP- AB5 13 B OUT 11 3500
T(L)-66 FTP- AB5 13 A OUT 11 11221
T(L)-66 FTP- AB5 13 A OUT 11 3400
T(L)-66 FTP- AB5 13 B OUT 11 612
T(L)-66 FTP- AB5 13 B OUT 11 3216
T(L)-54 S0C0 AA5 13 B IN 11 1650
T(L)-54 S0C0 AA5 13 B IN 11 1040
T(L)-66 S0J0 AA5 13 B IN 11 3168
T(L)-66 S0J0 AA5 13 A IN 11 3500
T-50 S00Z AA5 13 A IN 8 3150
T-50 S00Z AA5 13 A IN 8 3450
T-54 S000 AA5 13 B IN 8 2415
T-54 S000 AA5 11 B IN 8 3400
T-54 S000 AA5 11 B IN 8 2176
F-60/84 8ECY AA5 23 B IN 10 3350
F-60/84 8ECY AA5 23 B IN 10 603
F-60/84 8ECY AA5 23 A IN 10 140
F-60/84 8ECY AA5 23 A IN 10 12451
F-78/96 8N5A AA5 23 A IN 10 1680
F-78/96 8NCA AA5 23 A IN 10 18547
F-78/96 8NCA AA5 23 A IN 10 540
...全文
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听雨停了 2018-02-01
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引用 10 楼 qq_39528261 的回复:
感谢听雨停了,Null可以设置为空吗?



SELECT a.规格,

	   a.数量区间,

	   isnull(cast(a.AA1 AS VARCHAR(20)),'')  AS AA1数量合计,	--改空，多了一个cast( as varchar(20))

       isnull(b.AA1,'')  AS AA1批数,							--改0

       isnull(a.AA2,'')  AS AA2数量合计,

       isnull(b.AA2,'')  AS AA2批数,

       isnull(a.AA5,'')  AS AA5数量合计,

       isnull(b.AA5,'')  AS AA5批数,

       isnull(a.AA7,'')  AS AA7数量合计,

       isnull(b.AA7,'')  AS AA7批数,

       isnull(a.AA9,'')  AS AA9数量合计,

       isnull(b.AA9,'')  AS AA9批数,

       isnull(a.AB5,'')  AS AB5数量合计,

       isnull(b.AB5,'')  AS AB5批数

FROM   tab4 a

       right JOIN Tab5 b

            ON  a.规格 = b.规格

                AND a.数量区间=b.数量区间

ORDER BY a.规格

qq_39528261 2018-02-01
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感谢听雨停了,Null可以设置为空吗?
听雨停了 2018-02-01
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引用 8 楼 qq_39528261 的回复:
回:听雨停了
不用考虑哦!谢谢您



use Tempdb

go

--> --> 听雨停了-->生成测试数据

 

if not object_id(N'Tempdb..#tab') is null

	drop table #tab

Go

Create table #tab([规格] nvarchar(27),[6] nvarchar(24),[工作站] nvarchar(23),[8] int,[9] nvarchar(21),[11] nvarchar(23),[12] int,[数量] int)

Insert #tab

select N'T(L)-54',N'S0C0',N'AA1',13,N'A',N'IN',11,3600 union all

select N'T(L)-54',N'S0C0',N'AA1',13,N'A',N'IN',11,21656 union all

select N'T(L)-54',N'S0C0',N'AA1',13,N'B',N'IN',11,3550 union all

select N'T(L)-54',N'S0J0',N'AA1',13,N'B',N'IN',11,3550 union all

select N'T(L)-66',N'SPX0',N'AA1',13,N'B',N'OUT',11,852 union all

select N'T(L)-66',N'S0J0',N'AA1',13,N'B',N'IN',11,3500 union all

select N'T(L)-66',N'S0Y4',N'AA1',13,N'B',N'IN',11,13500 union all

select N'T(L)-66',N'S0Y4',N'AA1',13,N'B',N'IN',11,1540 union all

select N'T(L)-66',N'S0Y4',N'AA1',13,N'B',N'IN',11,3450 union all

select N'T(L)-66',N'S0Y4',N'AA2',13,N'B',N'IN',11,3450 union all

select N'T(L)-66',N'S0Y4',N'AA2',13,N'B',N'IN',11,207 union all

select N'T(L)-66',N'S0Y4',N'AA2',13,N'A',N'IN',11,3400 union all

select N'T-54',N'S000',N'AA2',13,N'A',N'IN',8,1156 union all

select N'T-54',N'S000',N'AA2',13,N'A',N'IN',8,540 union all

select N'T-54',N'SP00',N'AA2',13,N'A',N'IN',8,1080 union all

select N'T-54',N'S000',N'AA2',13,N'B',N'IN',8,640 union all

select N'T-54',N'SP00',N'AA2',13,N'A',N'IN',8,18000 union all

select N'T-54',N'S000',N'AA2',13,N'B',N'IN',8,480 union all

select N'T-54',N'S00Z',N'AA1',13,N'A',N'IN',8,3450 union all

select N'T-54',N'S00Z',N'AA1',13,N'A',N'IN',8,690 union all

select N'T-54',N'S00Z',N'AA1',13,N'A',N'IN',8,3400 union all

select N'T-54',N'S00Z',N'AA7',13,N'A',N'IN',8,1020 union all

select N'T-54',N'S00Z',N'AA7',13,N'A',N'IN',8,3350 union all

select N'T-66',N'S0F0',N'AA7',13,N'A',N'OUT',8,938 union all

select N'T-66',N'SPF0',N'AA7',13,N'A',N'OUT',8,3300 union all

select N'T-66',N'SPF0',N'AA7',13,N'A',N'OUT',8,264 union all

select N'T-66',N'S0F0',N'AA1',13,N'B',N'OUT',8,2340 union all

select N'T-66',N'SPF0',N'AA7',13,N'B',N'OUT',8,3600 union all

select N'T(L)-66',N'8SCT',N'AA1',13,N'A',N'IN',11,1224 union all

select N'T(L)-66',N'8SCT',N'AA1',13,N'A',N'IN',11,3550 union all

select N'T(L)-66',N'8SCT',N'AA1',13,N'B',N'IN',11,3550 union all

select N'T(L)-66',N'8SCT',N'AA1',13,N'A',N'IN',11,1917 union all

select N'T-66',N'C',N'AA1',13,N'A',N'OUT',8,3500 union all

select N'T-66',N'C',N'AA1',13,N'A',N'OUT',8,1330 union all

select N'T-66',N'C',N'AA1',13,N'B',N'OUT',8,3450 union all

select N'T-66',N'C',N'AA1',13,N'B',N'OUT',8,2346 union all

select N'T-86',N'D',N'AA1',13,N'B',N'OUT',8,3400 union all

select N'T-86',N'D',N'AA1',13,N'A',N'OUT',8,136 union all

select N'T-54',N'FTP-',N'AA1',13,N'A',N'OUT',11,3283 union all

select N'T(L)-66',N'FTP-',N'AA1',13,N'A',N'OUT',11,1848 union all

select N'T(L)-66',N'FTP-',N'AA1',13,N'A',N'OUT',11,216 union all

select N'T(L)-66',N'FTP-',N'AA1',13,N'A',N'OUT',11,3550 union all

select N'T(L)-66',N'FTP-',N'AA1',13,N'A',N'OUT',11,3550 union all

select N'T-66',N'FTP-',N'AA1',13,N'A',N'OUT',8,1917 union all

select N'T-66',N'FTP-',N'AA1',13,N'B',N'OUT',8,3550 union all

select N'T(L)-66',N'SPX0',N'AA9',13,N'B',N'OUT',11,3500 union all

select N'T(L)-66',N'SPX0',N'AA9',13,N'B',N'OUT',11,3500 union all

select N'T(L)-66',N'S0J0',N'AA9',13,N'A',N'IN',11,1330 union all

select N'T(L)-66',N'SPX0',N'AA9',13,N'A',N'OUT',11,3450 union all

select N'T(L)-66',N'SPX0',N'AA9',13,N'A',N'OUT',11,2760 union all

select N'T(L)-66',N'S0Y4',N'AA9',13,N'A',N'IN',11,3400 union all

select N'T-54',N'S000',N'AA9',13,N'A',N'IN',8,1876 union all

select N'T-54',N'SP00',N'AA9',13,N'B',N'IN',8,3500 union all

select N'T-54',N'S000',N'AA9',13,N'B',N'IN',8,576 union all

select N'T-54',N'SP00',N'AA9',13,N'B',N'IN',8,720 union all

select N'T-54',N'SP00',N'AA9',13,N'B',N'IN',8,720 union all

select N'T-54',N'S000',N'AA9',13,N'B',N'IN',8,12244 union all

select N'T-54',N'S000',N'AA9',13,N'B',N'IN',8,12094 union all

select N'T-54',N'S00Z',N'AA9',13,N'B',N'IN',8,22551 union all

select N'T-54',N'S00Z',N'AA9',13,N'B',N'IN',8,12227 union all

select N'T-54',N'S00Z',N'AA9',13,N'A',N'IN',8,600 union all

select N'T-54',N'S00Z',N'AA9',13,N'A',N'IN',8,180 union all

select N'T-66',N'SPF0',N'AA9',13,N'A',N'OUT',8,180 union all

select N'T-66',N'SPF0',N'AA9',13,N'A',N'OUT',8,180 union all

select N'T-66',N'SPF0',N'AA9',13,N'A',N'OUT',8,360 union all

select N'T-66',N'SPF0',N'AA9',13,N'B',N'OUT',8,480 union all

select N'T(L)-66',N'FSCG',N'AA9',13,N'A',N'OUT',11,756 union all

select N'T(L)-66',N'FSCT',N'AA9',13,N'B',N'OUT',11,160 union all

select N'T-54',N'C',N'AA9',13,N'A',N'OUT',8,160 union all

select N'T-86',N'D',N'AA9',13,N'A',N'OUT',8,2736 union all

select N'T(L)-54',N'FTP-',N'AA9',13,N'B',N'OUT',11,3550 union all

select N'T(L)-54',N'FTP-',N'AA9',13,N'B',N'OUT',11,2769 union all

select N'T(L)-54',N'FTP-',N'AA9',13,N'B',N'OUT',11,3500 union all

select N'T-54',N'YSP-',N'AA9',13,N'B',N'IN',8,3430 union all

select N'T-54',N'YSP-',N'AA9',13,N'B',N'IN',8,13450 union all

select N'T-54',N'YSP-',N'AA9',13,N'A',N'IN',8,1311 union all

select N'T-54',N'YSP-',N'AA9',13,N'A',N'IN',8,3332 union all

select N'T-66',N'FTP-',N'AA9',13,N'A',N'OUT',8,2680 union all

select N'T-66',N'FTP-',N'AA9',13,N'A',N'OUT',8,1914 union all

select N'T-66',N'FTP-',N'AA9',13,N'A',N'OUT',8,2015 union all

select N'T-66',N'FTP-',N'AA9',13,N'A',N'OUT',8,3168 union all

select N'T-66',N'FTP-',N'AA9',13,N'B',N'OUT',8,3479 union all

select N'T-66',N'C',N'AB5',13,N'A',N'OUT',8,3266 union all

select N'T-66',N'C',N'AB5',13,N'B',N'OUT',8,3500 union all

select N'T(L)-66',N'FTP-',N'AB5',13,N'B',N'OUT',11,3500 union all

select N'T(L)-66',N'FTP-',N'AB5',13,N'A',N'OUT',11,11221 union all

select N'T(L)-66',N'FTP-',N'AB5',13,N'A',N'OUT',11,3400 union all

select N'T(L)-66',N'FTP-',N'AB5',13,N'B',N'OUT',11,612 union all

select N'T(L)-66',N'FTP-',N'AB5',13,N'B',N'OUT',11,3216 union all

select N'T(L)-54',N'S0C0',N'AA5',13,N'B',N'IN',11,1650 union all

select N'T(L)-54',N'S0C0',N'AA5',13,N'B',N'IN',11,1040 union all

select N'T(L)-66',N'S0J0',N'AA5',13,N'B',N'IN',11,3168 union all

select N'T(L)-66',N'S0J0',N'AA5',13,N'A',N'IN',11,3500 union all

select N'T-50',N'S00Z',N'AA5',13,N'A',N'IN',8,3150 union all

select N'T-50',N'S00Z',N'AA5',13,N'A',N'IN',8,3450 union all

select N'T-54',N'S000',N'AA5',13,N'B',N'IN',8,2415 union all

select N'T-54',N'S000',N'AA5',11,N'B',N'IN',8,3400 union all

select N'T-54',N'S000',N'AA5',11,N'B',N'IN',8,2176 union all

select N'F-60/84',N'8ECY',N'AA5',23,N'B',N'IN',10,3350 union all

select N'F-60/84',N'8ECY',N'AA5',23,N'B',N'IN',10,603 union all

select N'F-60/84',N'8ECY',N'AA5',23,N'A',N'IN',10,140 union all

select N'F-60/84',N'8ECY',N'AA5',23,N'A',N'IN',10,12451 union all

select N'F-78/96',N'8N5A',N'AA5',23,N'A',N'IN',10,1680 union all

select N'F-78/96',N'8NCA',N'AA5',23,N'A',N'IN',10,18547 union all

select N'F-78/96',N'8NCA',N'AA5',23,N'A',N'IN',10,540

Go

Select * from #tab

--测试数据结束





--按规格,工作站,数量区间,聚合数量插入#tab2中

;WITH cte AS (

SELECT *,

       CASE 

            WHEN 数量 < 1000 THEN '<1000'

            WHEN 数量 BETWEEN 1000 AND 5000 THEN '1000-5000'

            WHEN 数量 BETWEEN 5000 AND 10000 THEN '5000-10000'

            WHEN 数量 BETWEEN 10000 AND 15000 THEN '10000-15000'

            WHEN 数量 BETWEEN 15000 AND 20000 THEN '15000-20000'

            WHEN 数量 > 20000 THEN '>20000'

       END AS [数量区间]

FROM #tab

)       

SELECT 规格,工作站,数量区间,sum(数量)as 数量合计 

INTO #tab2

FROM cte

GROUP BY 规格,工作站,数量区间



--按规格,工作站,数量区间，聚合批数插入#tab3中

;WITH cte AS (

SELECT *,

       CASE 

            WHEN 数量 < 1000 THEN '<1000'

            WHEN 数量 BETWEEN 1000 AND 5000 THEN '1000-5000'

            WHEN 数量 BETWEEN 5000 AND 10000 THEN '5000-10000'

            WHEN 数量 BETWEEN 10000 AND 15000 THEN '10000-15000'

            WHEN 数量 BETWEEN 15000 AND 20000 THEN '15000-20000'

            WHEN 数量 > 20000 THEN '>20000'

       END AS [数量区间]

FROM #tab

)

SELECT 规格,工作站,数量区间,count(1) as cnt

INTO #tab3

FROM cte

GROUP BY 规格,工作站,数量区间







--数量行专列插入tab4中

IF OBJECT_ID('tab4') IS NOT NULL

	DROP TABLE tab4

DECLARE @name VARCHAR(max),@sql VARCHAR(max)

set @name =stuff((SELECT DISTINCT ',['+[工作站]+']'  from #tab2 for xml PATH('')),1,1,'')

set @sql ='SELECT * into tab4 from #tab2 pivot(max(数量合计)for [工作站] in('+@name+'))a'

EXEC( @sql)

SELECT * FROM tab4



--批数行转列插入tab5中

IF OBJECT_ID('tab5') IS NOT NULL

	DROP TABLE tab5

DECLARE @name2 VARCHAR(max),@sql2 VARCHAR(max)

set @name2 =stuff((SELECT DISTINCT ',['+[工作站]+']'  from #tab3 for xml PATH('')),1,1,'')

set @sql2 ='SELECT * into tab5 from #tab3 pivot(max(cnt)for [工作站] in('+@name2+'))a'

EXEC( @sql2)

SELECT * FROM tab5



--两表联合查询出结果

SELECT a.规格,

	   a.数量区间,

	   a.AA1  AS AA1数量合计,

       b.AA1  AS AA1批数,

       a.AA2  AS AA2数量合计,

       b.AA2  AS AA2批数,

       a.AA5  AS AA5数量合计,

       b.AA5  AS AA5批数,

       a.AA7  AS AA7数量合计,

       b.AA7  AS AA7批数,

       a.AA9  AS AA9数量合计,

       b.AA9  AS AA9批数,

       a.AB5  AS AB5数量合计,

       b.AB5  AS AB5批数

FROM   tab4 a

       right JOIN Tab5 b

            ON  a.规格 = b.规格

                AND a.数量区间=b.数量区间

ORDER BY a.规格

qq_39528261 2018-02-01
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回:听雨停了 不用考虑哦!谢谢您
听雨停了 2018-02-01
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引用 6 楼 qq_39528261 的回复:
二月十六版主,我表述明白了吗?
字段6里的in/out需要考虑进数量的sum中吗？
qq_39528261 2018-02-01
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二月十六版主,我表述明白了吗?
qq_39528261 2018-02-01
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版主请看此图,
1,2代表列标题名称,
我发帖考虑欠周,不好意思!
二月十六 2018-02-01
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引用 3 楼 qq_39528261 的回复:
谢谢二月十六版主,每次得到您的帮助, 规则请参考附图,可能更好理解!
没看明白规则 另外 1 2 规格 6 工作站 8 9 11 12 数量 T(L)-54 S0C0 AA1 13 A IN 11 3600 这个表字段1 2的是什么？
qq_39528261 2018-02-01
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谢谢二月十六版主,每次得到您的帮助, 规则请参考附图,可能更好理解!
qq_39528261 2018-02-01
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依规格工作站计算出区间数量及总批数
二月十六 2018-02-01
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7天带你玩转Mysql数据库之SQL语句
您观看课程学习后免费入群领取【超全Python资料包+17本学习电子书】 七年SQL语句编写经验。满满的干货！ 在网上找了好多SQL数据库的教程，但你还会面临这样的问题：1. 自己写了SQL却不知道对不对。2. 在上线后发现原有的数据内容SQL语句执⾏结果没问题， 但是数据变化了以后SQL返回的结果就错误了。3. 稍微复杂⼀点的SQL就不知道该如何写了。4. 看不懂同⾏写的SQL是为什么。5. 不知道索引的原理。6. 不知道怎么加索引能够提⾼查询性能纵观全网的教程都只停留在概念解析的层面，没有深入剖析原理，所以看了那么多的教程，可还是不会写。本教程与其他教程不同带你深入了解原理，让你真正了解什么是SQL语句，让你懂得SQL语句的编写⽅法。不再为SQL语句而烦恼。真正做到面对任何问题能够判断出SQL语句是不是能够实现，该怎样实现。 
sql中条件语句
前言： 最近被好多琐事缠身，下个礼拜开始就要开始今年遥遥出差的日子了，各位测试小伙伴做过长期需要测试出差的项目吗。哎，话不多说，珍惜现在为数不多的自由时光吧。 最近呢，在帮公司面试招人，但是我发现有很多测试小伙伴sql能力好差，各个数据库我们不谈，就光说sql语句而言个人还是感觉比较简单。今天就说一下sql中的条件语句。 什么是条件语句 可能有部分小伙伴会发出疑问，sql还有条件语句？下面直接看例子。其实概念很简单，但是如何举例子可真是愁死我了。哈哈。 下面看看具体写法吧。 case when 条件1 th
用sql语句进行不同条件的统计
进行不同条件的统计是case表达式著名用法之一，我们统计各个班级男女的性别数量： 如图：班级，性别，人数 我现在统计所有班级男生数量： select sum(person_num) as person_num from school_room where sex = '1' 统计所有女生的人数： select sum(person_num) as person_num from school_room where sex = '2' 我i们使用case表
MySql：一条sql语句多个count统计
MySQL一条sql语句多个count统计
SQL语句——查询
SQL 语句 单表查询 查询语句（SELECT）是数据库中最基本的和最重要的语句之一，其功能是从数据库中检索满足条件的数据。查询的数据源可以来自一张表，也可以来自多张表甚至来自视图，查询的结果是由0行（没有满足条件的数据）或多行记录组成的一个记录集合，并允许选择一个或多个字段作为输出字段。SELECT语句还可以对查询结果进行排序、汇总等。查询语句的基本结构可描述为： SELECT <目标列名序列> -- 需要哪些列 FROM <表名> [JOIN <表名> ON <
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