我有三张桌子：a，b和c
a：（q，r，s），b：（q，r，t），c：（q，r，u，v）
我想做一个这样的查询：
select q,r from a where s="whatever", q="whatever"
select q,r from b where t="whatever", q="whatever"
select q,r from c where u="whatever", q="whatever"
我希望结果在一个查询中，按r排序。这可能吗？
答案 0 :(得分：1)
您可以使用SQL UNION运算符。它用于组合2个或更多SELECT语句的结果集。它删除了各种SELECT语句之间的重复行。
UNION中的每个SELECT语句必须在具有相似数据类型的结果集中具有相同数量的字段。
示例：
> gcc -O3 -g -std=c11 -Wall -Wextra -Wmissing-prototypes
> -Wstrict-prototypes -Wold-style-definition -Werror -o working working.c dave@hellion:/home/home/dave/src/ringbuffer/src$ ./working
> 2.2 4.3 6.0 8.0 10.0 12.0
> 3.2 6.3 9.0 12.0 15.0 18.0
> 4.2 8.3 12.0 16.0 20.0 24.0
> 5.2 10.3 15.0 20.0 25.0 30.0
> 6.2 12.3 18.0 24.0 30.0 36.0
> 7.2 14.3 21.0 28.0 35.0 42.0
> 8.2 16.3 24.0 32.0 40.0 48.0
> 9.2 18.3 27.0 36.0 45.0 54.0
> 10.2 20.3 30.0 40.0 50.0 60.0
> 11.2 22.3 33.0 44.0 55.0 66.0
> 12.2 24.3 36.0 48.0 60.0 72.0
> 13.2 26.3 39.0 52.0 65.0 78.0
> 14.2 28.3 42.0 56.0 70.0 84.0
> 15.2 30.3 45.0 60.0 75.0 90.0
> 16.2 32.3 48.0 64.0 80.0 96.0
> 17.2 34.3 51.0 68.0 85.0 102.0
> 18.2 36.3 54.0 72.0 90.0 108.0
> 19.2 38.3 57.0 76.0 95.0 114.0
> 20.2 40.3 60.0 80.0 100.0 120.0
> 21.2 42.3 63.0 84.0 105.0 126.0
> 22.2 44.3 66.0 88.0 110.0 132.0
> 23.2 46.3 69.0 92.0 115.0 138.0
> 24.2 48.3 72.0 96.0 120.0 144.0
> 25.2 50.3 75.0 100.0 125.0 150.0
> 26.2 52.3 78.0 104.0 130.0 156.0
> 27.2 54.3 81.0 108.0 135.0 162.0
> 28.2 56.3 84.0 112.0 140.0 168.0
> 29.2 58.3 87.0 116.0 145.0 174.0
> 30.2 60.3 90.0 120.0 150.0 180.0
> 31.2 62.3 93.0 124.0 155.0 186.0
> 32.2 64.3 96.0 128.0 160.0 192.0
> 33.2 66.3 99.0 132.0 165.0 198.0
> 34.2 68.3 102.0 136.0 170.0 204.0
> 35.2 70.3 105.0 140.0 175.0 210.0
> 36.2 72.3 108.0 144.0 180.0 216.0
> 37.2 74.3 111.0 148.0 185.0 222.0
> 38.2 76.3 114.0 152.0 190.0 228.0
> 39.2 78.3 117.0 156.0 195.0 234.0
> 40.2 80.3 120.0 160.0 200.0 240.0
> 41.2 82.3 123.0 164.0 205.0 246.0
> 42.2 84.3 126.0 168.0 210.0 252.0
> 43.2 86.3 129.0 172.0 215.0 258.0
> 44.2 88.3 132.0 176.0 220.0 264.0
> 45.2 90.3 135.0 180.0 225.0 270.0
> 46.2 92.3 138.0 184.0 230.0 276.0
> 47.2 94.3 141.0 188.0 235.0 282.0
> 48.2 96.3 144.0 192.0 240.0 288.0
> 49.2 98.3 147.0 196.0 245.0 294.0
> 50.2 100.3 150.0 200.0 250.0 300.0
> 51.2 102.3 153.0 204.0 255.0 306.0
> 2.2 4.3 6.0 8.0 10.0 12.0
> 3.2 6.3 9.0 12.0 15.0 18.0
> 4.2 8.3 12.0 16.0 20.0 24.0
> 5.2 10.3 15.0 20.0 25.0 30.0
> 6.2 12.3 18.0 24.0 30.0 36.0
> 7.2 14.3 21.0 28.0 35.0 42.0
> 8.2 16.3 24.0 32.0 40.0 48.0
> 9.2 18.3 27.0 36.0 45.0 54.0
> 10.2 20.3 30.0 40.0 50.0 60.0
> 11.2 22.3 33.0 44.0 55.0 66.0
> 12.2 24.3 36.0 48.0 60.0 72.0
> 13.2 26.3 39.0 52.0 65.0 78.0
> 14.2 28.3 42.0 56.0 70.0 84.0
> 15.2 30.3 45.0 60.0 75.0 90.0
> 16.2 32.3 48.0 64.0 80.0 96.0
> 17.2 34.3 51.0 68.0 85.0 102.0
> 18.2 36.3 54.0 72.0 90.0 108.0
> 19.2 38.3 57.0 76.0 95.0 114.0
> 20.2 40.3 60.0 80.0 100.0 120.0
> 21.2 42.3 63.0 84.0 105.0 126.0
> 22.2 44.3 66.0 88.0 110.0 132.0
> 23.2 46.3 69.0 92.0 115.0 138.0
> 24.2 48.3 72.0 96.0 120.0 144.0
> 25.2 50.3 75.0 100.0 125.0 150.0
> 26.2 52.3 78.0 104.0 130.0 156.0
> 27.2 54.3 81.0 108.0 135.0 162.0
> 28.2 56.3 84.0 112.0 140.0 168.0
> 29.2 58.3 87.0 116.0 145.0 174.0
> 30.2 60.3 90.0 120.0 150.0 180.0
> 31.2 62.3 93.0 124.0 155.0 186.0
> 32.2 64.3 96.0 128.0 160.0 192.0
> 33.2 66.3 99.0 132.0 165.0 198.0
> 34.2 68.3 102.0 136.0 170.0 204.0
> 35.2 70.3 105.0 140.0 175.0 210.0
> 36.2 72.3 108.0 144.0 180.0 216.0
> 37.2 74.3 111.0 148.0 185.0 222.0
> 38.2 76.3 114.0 152.0 190.0 228.0
> 39.2 78.3 117.0 156.0 195.0 234.0
> 40.2 80.3 120.0 160.0 200.0 240.0
> 41.2 82.3 123.0 164.0 205.0 246.0
> 42.2 84.3 126.0 168.0 210.0 252.0
> 43.2 86.3 129.0 172.0 215.0 258.0
> 44.2 88.3 132.0 176.0 220.0 264.0
> 45.2 90.3 135.0 180.0 225.0 270.0
> 46.2 92.3 138.0 184.0 230.0 276.0
> 47.2 94.3 141.0 188.0 235.0 282.0
> 48.2 96.3 144.0 192.0 240.0 288.0
> 49.2 98.3 147.0 196.0 245.0 294.0
> 50.2 100.3 150.0 200.0 250.0 300.0
> 51.2 102.3 153.0 204.0 255.0 306.0
您可以使用UNION ALL而不是UNION。它们之间的区别在于 UNION ALL 不会删除重复的行。