我的理解是,大多数 OR 条件都可以在 UNION ALL 的性能优势处被替换。但是对于这 2 个查询,Count ('1') 是不一样的。为什么会这样-我在这里遗漏了什么。应该不一样吧。有人能解释一下差距吗
SQL #1
sel
D1.COL_1_CD, D1.COL_1_DESC,
D2.COL_2_CD, D2.COL_2_DESC, D3.COL_3_CD, D3.COL_3_DESC, D4.COL_4_CD,
D4.COL_4_DESC, D5.COL_5_CD, D5.COL_5_DESC,
d1.COL_1_CD_SYS_ID,
d2.COL_2_CD_SYS_ID,
d3.COL_3_CD_SYS_ID,
d4.COL_4_CD_SYS_ID,
d5.COL_5_CD_SYS_ID
from
D1,
D2, D3, D4,
D5
where
D1.COL_1_CD1=D2.COL_2_CD1
and
D2.COL_2_CD1=D3.COL_3_CD1
and
D4.COL_4_CD1=D5.COL_5_CD1
and
(D1.COL_1_CD in ('707')
or D2.COL_2_CD in ('707')
or D3.COL_3_CD in ('707')
or D4.COL_4_CD in ('707')
or D5.COL_5_CD in ('707') )
group by 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
SQL #2
sel
D1.COL_1_CD, D1.COL_1_DESC,
D2.COL_2_CD, D2.COL_2_DESC, D3.COL_3_CD, D3.COL_3_DESC, D4.COL_4_CD,
D4.COL_4_DESC, D5.COL_5_CD, D5.COL_5_DESC,
d1.COL_1_CD_SYS_ID,
d2.COL_2_CD_SYS_ID,
d3.COL_3_CD_SYS_ID,
d4.COL_4_CD_SYS_ID,
d5.COL_5_CD_SYS_ID
from
D1,
D2, D3, D4,
D5
where
D1.COL_1_CD1=D2.COL_2_CD1
and
D2.COL_2_CD1=D3.COL_3_CD1
and
D4.COL_4_CD1=D5.COL_5_CD1
and
D1.COL_1_CD in ('707')
UNION ALL
sel
D1.COL_1_CD, D1.COL_1_DESC,
D2.COL_2_CD, D2.COL_2_DESC, D3.COL_3_CD, D3.COL_3_DESC, D4.COL_4_CD,
D4.COL_4_DESC, D5.COL_5_CD, D5.COL_5_DESC,
d1.COL_1_CD_SYS_ID,
d2.COL_2_CD_SYS_ID,
d3.COL_3_CD_SYS_ID,
d4.COL_4_CD_SYS_ID,
d5.COL_5_CD_SYS_ID
from
D1,
D2, D3, D4,
D5
where
D1.COL_1_CD1=D2.COL_2_CD1
and
D2.COL_2_CD1=D3.COL_3_CD1
and
D4.COL_4_CD1=D5.COL_5_CD1
and
D2.COL_2_CD in ('707')
UNION ALL
.....<same query>
D3.COL_3_CD in ('707')
UNION ALL
.....<same query>
D4.COL_4_CD in ('707')
UNION ALL
.....<same query>
D5.COL_5_CD in ('707')
行数不一样。什么样的OR逻辑可以转换为等价的UNION ALL。