| PostgreSQL 9.6.0 锟街诧拷
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| 锟斤拷一页 | 锟斤拷一锟斤拷 | 锟斤拷 9. 锟斤拷锟斤拷锟酵诧拷锟斤拷锟斤拷 | 锟斤拷一页 |
锟斤拷锟斤拷锟侥比较诧拷锟斤拷锟斤拷锟斤拷锟斤拷锟矫ｏ拷锟斤拷锟斤拷 9-1锟斤拷示锟斤拷
锟斤拷 9-1. 锟饺较诧拷锟斤拷锟斤拷
| 锟斤拷锟斤拷锟斤拷 | 锟斤拷锟斤拷 |
|---|---|
| < | 小锟斤拷 |
| > | 锟斤拷锟斤拷 |
| <= | 小锟节碉拷锟斤拷 |
| >= | 锟斤拷锟节碉拷锟斤拷 |
| = | 锟斤拷锟斤拷 |
| <> or != | 锟斤拷锟斤拷锟斤拷 |
注锟斤拷: !=锟斤拷锟斤拷锟斤拷锟节凤拷锟斤拷锟斤拷锟阶段憋拷转锟斤拷锟斤拷<>锟斤拷锟斤拷锟杰帮拷!=锟斤拷<>锟斤拷锟斤拷锟斤拷实锟斤拷为锟斤拷锟斤拷同锟斤拷锟铰★拷
锟饺较诧拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟叫匡拷锟皆比较碉拷锟斤拷锟斤拷锟斤拷锟酵★拷锟斤拷锟叫比较诧拷锟斤拷锟斤拷锟斤拷锟斤拷双目锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟角凤拷锟斤拷boolean锟斤拷锟酵ｏ拷锟斤拷锟斤拷锟斤拷1 < 2 < 3锟侥憋拷锟斤拷式锟角非凤拷锟侥ｏ拷锟斤拷为没锟斤拷<锟斤拷锟斤拷锟斤拷锟斤拷锟皆比斤拷一锟斤拷锟斤拷锟斤拷值锟斤拷3锟斤拷锟斤拷
锟斤拷锟斤拷 9-2锟斤拷示锟斤拷也锟斤拷一些锟饺斤拷谓锟绞★拷 锟斤拷锟角碉拷锟斤拷为锟酵诧拷锟斤拷锟斤拷锟斤拷锟今，碉拷锟角撅拷锟斤拷 SQL 锟斤拷准锟斤拷要锟斤拷锟斤拷锟斤拷锟斤拷锓拷锟�
锟斤拷 9-2. 锟饺斤拷谓锟斤拷
| 谓锟斤拷 | 锟斤拷锟斤拷 |
|---|---|
| a BETWEEN x AND y | 锟斤拷x锟斤拷y之锟斤拷 |
| a NOT BETWEEN x AND y | 锟斤拷锟斤拷x锟斤拷y之锟斤拷 |
| a BETWEEN SYMMETRIC x AND y | 锟节对比斤拷值锟斤拷锟斤拷锟轿伙拷锟絰锟斤拷y之锟斤拷 |
| a NOT BETWEEN SYMMETRIC x AND y | 锟节对比斤拷值锟斤拷锟斤拷锟轿伙拷锟絰锟斤拷y之锟斤拷 |
| a IS DISTINCT FROM b | 锟斤拷锟斤拷锟节ｏ拷锟斤拷值锟斤拷锟斤拷锟斤拷一锟斤拷锟斤拷通值 |
| a IS NOT DISTINCT FROM b | 锟斤拷锟节ｏ拷锟斤拷值锟斤拷锟斤拷锟斤拷一锟斤拷锟斤拷通值 |
| expression IS NULL | 锟角匡拷值 |
| expression IS NOT NULL | 锟斤拷锟角匡拷值 |
| expression ISNULL | 锟角匡拷值锟斤拷锟角憋拷准锟斤法锟斤拷 |
| expression NOTNULL | 锟斤拷锟角匡拷值锟斤拷锟角憋拷准锟斤法锟斤拷 |
| boolean_expression IS TRUE | 为锟斤拷 |
| boolean_expression IS NOT TRUE | 为锟劫伙拷未知 |
| boolean_expression IS FALSE | 为锟斤拷 |
| boolean_expression IS NOT FALSE | 为锟斤拷锟斤拷锟轿粗� |
| boolean_expression IS UNKNOWN | 值为未知 |
| boolean_expression IS NOT UNKNOWN | 为锟斤拷锟斤拷锟轿拷锟� |
锟斤拷锟剿比较诧拷锟斤拷锟斤拷锟斤拷锟解，锟斤拷锟斤拷锟�BETWEEN锟结构也锟斤拷锟斤拷使锟矫ｏ拷
a BETWEEN x AND y
锟斤拷效锟斤拷
a >= x AND a <= y
注锟斤拷BETWEEN锟斤拷为锟秸碉拷值锟角帮拷锟斤拷锟节凤拷围锟节的★拷 NOT BETWEEN锟斤拷锟斤拷锟斤拷锟洁反锟饺较ｏ拷
a NOT BETWEEN x AND y
锟斤拷效锟斤拷
a < x OR a > y
BETWEEN SYMMETRIC锟斤拷BETWEEN锟斤拷同锟斤拷锟斤拷锟斤拷BETWEEN SYMMETRIC锟斤拷要锟斤拷AND锟斤拷叩牟锟斤拷锟叫★拷诨锟斤拷锟斤拷锟揭边的诧拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷小锟节碉拷锟斤拷锟揭诧拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟皆讹拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟角伙拷应锟斤拷一锟斤拷锟角空凤拷围锟斤拷
锟斤拷锟斤拷一锟斤拷锟斤拷锟斤拷为锟斤拷时锟斤拷锟斤拷通锟侥比较诧拷锟斤拷锟斤拷锟斤拷玫锟斤拷眨锟斤拷锟绞�"未知"锟斤拷锟斤拷 锟斤拷锟斤拷锟斤拷锟斤拷锟劫★拷锟斤拷锟界，7 = NULL锟矫碉拷锟秸ｏ拷7 <> NULL 也一锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟轿拷锟斤拷锟斤拷剩锟斤拷锟斤拷锟绞癸拷锟� IS [ NOT ] DISTINCT FROM谓锟绞ｏ拷
a IS DISTINCT FROM b a IS NOT DISTINCT FROM b
锟斤拷锟节非匡拷锟斤拷锟诫，IS DISTINCT FROM锟斤拷<> 锟斤拷锟斤拷锟斤拷一锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷攵嘉拷眨锟斤拷锟斤拷岱碉拷丶佟锟斤拷锟斤拷锟斤拷只锟斤拷一锟斤拷锟斤拷锟斤拷为锟秸ｏ拷 锟斤拷锟结返锟斤拷锟芥。锟斤拷锟狡地ｏ拷IS NOT DISTINCT FROM 锟斤拷锟节非匡拷锟斤拷锟斤拷锟斤拷锟轿拷锟�=锟斤拷同锟斤拷锟斤拷锟角碉拷锟斤拷锟斤拷锟斤拷锟诫都为锟斤拷时锟斤拷锟斤拷锟斤拷锟芥， 锟斤拷锟揭碉拷只锟斤拷一锟斤拷锟斤拷锟斤拷为锟斤拷时锟斤拷锟截假★拷锟斤拷耍锟� 锟斤拷些谓锟斤拷实锟斤拷锟较把匡拷值锟斤拷锟斤拷一锟斤拷锟斤拷通锟斤拷锟斤拷值锟斤拷锟斤拷锟斤拷"unknown"锟斤拷
要锟斤拷锟揭伙拷锟街碉拷欠锟轿拷眨锟绞癸拷锟斤拷锟斤拷锟侥结构锟斤拷
expression IS NULL expression IS NOT NULL
锟斤拷锟竭碉拷效锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷准锟侥结构锟斤拷
expression ISNULL expression NOTNULL
锟斤拷要写expression = NULL锟斤拷锟斤拷为NULL锟角诧拷"锟斤拷锟斤拷"NULL锟侥ｏ拷锟斤拷锟狡达拷锟斤拷一锟斤拷未知锟斤拷值锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷薹锟街拷锟斤拷锟斤拷锟轿粗拷锟斤拷锟街碉拷欠锟斤拷锟饺ｏ拷锟斤拷锟斤拷锟斤拷锟斤拷为锟斤拷锟斤拷 SQL 锟斤拷准锟斤拷
锟斤拷示: 锟斤拷些应锟矫匡拷锟斤拷要锟斤拷锟斤拷锟绞�expression = NULL锟斤拷expression锟矫筹拷锟斤拷值时锟斤拷锟斤拷锟芥。锟斤拷锟斤拷强锟揭斤拷锟斤拷锟斤拷锟斤拷锟斤拷应锟斤拷锟睫改筹拷锟斤拷循 SQL 锟斤拷准锟斤拷锟斤拷锟角ｏ拷锟斤拷锟斤拷锟斤拷锟斤拷薷牟锟斤拷锟斤拷锟斤拷锟缴ｏ拷锟斤拷么锟斤拷锟角匡拷锟斤拷使锟斤拷锟斤拷锟矫憋拷锟斤拷transform_null_equals锟斤拷锟斤拷锟斤拷锟斤拷锟斤拷锟�PostgreSQL锟斤拷锟斤拷x = NULL锟接撅拷转锟斤拷锟斤拷x IS NULL锟斤拷
锟斤拷锟斤拷值也锟斤拷锟斤拷使锟斤拷锟斤拷锟叫结构锟斤拷锟叫诧拷锟皆ｏ拷
boolean_expression IS TRUE boolean_expression IS NOT TRUE boolean_expression IS FALSE boolean_expression IS NOT FALSE boolean_expression IS UNKNOWN boolean_expression IS NOT UNKNOWN
锟斤拷些锟结构锟斤拷锟斤拷锟角凤拷锟斤拷锟斤拷锟劫ｏ拷锟斤拷锟斤拷锟斤拷锟斤拷锟截匡拷值锟斤拷锟斤拷使锟斤拷锟斤拷锟斤拷锟角匡拷也锟斤拷恕锟斤拷锟街碉拷锟斤拷氡伙拷锟斤拷锟斤拷呒锟街�"未知"锟斤拷 锟斤拷注锟斤拷实锟斤拷锟斤拷IS UNKNOWN锟斤拷IS NOT UNKNOWN锟街憋拷锟斤拷IS NULL锟斤拷IS NOT NULL锟斤拷同锟斤拷 只锟斤拷锟斤拷锟斤拷锟斤拷锟绞斤拷锟斤拷锟斤拷遣锟斤拷锟斤拷锟斤拷汀锟�
锟斤拷锟斤拷 9-3锟斤拷锟斤拷示锟斤拷 也锟斤拷一些锟饺斤拷锟斤拷氐暮锟斤拷锟斤拷锟斤拷谩锟�