SQL开发实例和优化

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## SQL开发实例和优化

flzhang 2017-09-07 16:45:52 浏览448

1,3
48,48
51,53
67,68
create table test.range_problem(

a int not null,
primary key (a));
insert into test.range_problem values(1);

insert into test.range_problem values(2);

insert into test.range_problem values(3);

insert into test.range_problem values(48);

insert into test.range_problem values(50);

insert into test.range_problem values(51);

insert into test.range_problem values(52);

insert into test.range_problem values(53);

insert into test.range_problem values(66);

insert into test.range_problem values(67);

--思路1 找最后一个不连续的数
SELECT T1.A
FROM test.range_problem T1
WHERE NOT EXISTS
(
SELECT A
FROM test.range_problem T2
WHERE T2.A -1 = T1.A
)

--思路2  找所有行对应的结束值
SELECT ROW_NUMBER()OVER(ORDER BY TBASE.A) ID
,TBASE.A
,(SELECT Min(A)
FROM test.range_problem T1
WHERE NOT EXISTS
(
SELECT A
FROM test.range_problem T2
WHERE T2.A -1 = T1.A
)
AND T1.A >= TBASE.A  --T1.A 是3,48,53,67 TBASE.A 是每行的值
) A_END

FROM test.range_problem TBASE

--思路3 分组后找出所有连续的起始值和结束值
SELECT MIN(A) A_START, A_END
FROM(
SELECT ROW_NUMBER()OVER(ORDER BY TBASE.A) ID
,TBASE.A
,(SELECT Min(A)
FROM test.range_problem T1
WHERE NOT EXISTS
(
SELECT A
FROM test.range_problem T2
WHERE T2.A -1 = T1.A
)
AND T1.A >= TBASE.A  --T1.A 是3,48,53,67 TBASE.A 是每行的值
) A_END

FROM test.range_problem TBASE
) T
GROUP BY T.A_END

--对上面语句的优化
WITH POT AS(
SELECT A
FROM test.range_problem T
WHERE NOT EXISTS
( SELECT A
FROM test.range_problem TC
WHERE TC.A -1 = T.A)
)

SELECT TBASE.A A_START,(SELECT MIN(A)
FROM  POT T
WHERE TBASE.A <= T.A
) A_END
FROM test.range_problem TBASE

flzhang
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