UNIQUE NULLS NOT DISTINCT
Recorded source states and original language descriptions. Missing version evidence stays unknown.
The source snapshot records transitions for PostgreSQL 8.1–18. The historical matrix records independent cells for 7.4–18. Neither records support for PostgreSQL 19 or 20; newer versions remain unknown. These source claims are distinct from runtime measurements.
Indexing & Constraints
Description
By default, NULL values are treated as distinct entries. Specifying NULLS NOT DISTINCT on unique indexes / constraints will cause NULL to be treated as not distinct, or in other words, equivalently.
Selected version: PostgreSQL 18
Yes
Compare versions
Original documentation links
Recorded legacy identifiers: 392
Complete source facts and provenance
yaml · center · 1dd22bf9a7f3ec325b894e2836fda535a25529f246a94dd41d6abbfe9997f7fd
{
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"SourceKey": "UNIQUE NULLS NOT DISTINCT",
"SourceHash": "1dd22bf9a7f3ec325b894e2836fda535a25529f246a94dd41d6abbfe9997f7fd",
"Name": "UNIQUE NULLS NOT DISTINCT",
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"name": "UNIQUE NULLS NOT DISTINCT",
"versions": {
"15": "Yes"
}
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"Texts": [
{
"Locale": "en",
"Title": "UNIQUE NULLS NOT DISTINCT",
"BodyHTML": "\u003cp\u003eBy default, \u003ccode\u003eNULL\u003c/code\u003e values are treated as distinct entries. Specifying \u003ccode\u003eNULLS NOT DISTINCT\u003c/code\u003e on unique indexes / constraints will cause \u003ccode\u003eNULL\u003c/code\u003e to be treated as not distinct, or in other words, equivalently.\u003c/p\u003e\n",
"SourceHash": "1dd22bf9a7f3ec325b894e2836fda535a25529f246a94dd41d6abbfe9997f7fd",
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"description": "By default, `NULL` values are treated as distinct entries. Specifying `NULLS NOT DISTINCT` on unique indexes / constraints will cause `NULL` to be treated as not distinct, or in other words, equivalently.",
"name": "UNIQUE NULLS NOT DISTINCT",
"versions": {
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},
{
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"Title": "UNIQUE NULLS NOT DISTINCT",
"BodyHTML": "\u003cp\u003e默认情况下 \u003ccode\u003eNULL\u003c/code\u003e 彼此不同；在唯一索引或唯一约束上指定 \u003ccode\u003eNULLS NOT DISTINCT\u003c/code\u003e 后，\u003ccode\u003eNULL\u003c/code\u003e 会被视为不再互异。\u003c/p\u003e\n",
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"description": "默认情况下 `NULL` 彼此不同；在唯一索引或唯一约束上指定 `NULLS NOT DISTINCT` 后，`NULL` 会被视为不再互异。",
"name": "UNIQUE NULLS NOT DISTINCT"
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"LegacyIDs": [
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}