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Comment:Attempt to clarify the scope of when UPSERT processing applies.
Timelines: family | ancestors | descendants | both | branch-3.28
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SHA3-256: aae75b6ac27f4553720bfc6464f3772a3d5fb042d09920daac90234c77f3199f
User & Date: drh 2019-05-02 16:25:02
Context
2019-05-10
11:38
Fix a typo in the documentation for ANALYZE. check-in: 0917d5f9d6 user: drh tags: branch-3.28
2019-05-02
16:25
Attempt to clarify the scope of when UPSERT processing applies. check-in: aae75b6ac2 user: drh tags: branch-3.28
2019-04-30
20:37
More "whynotgit.html" updates. check-in: 71cccf3d65 user: drh tags: branch-3.28
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<p>An UPSERT is an ordinary [INSERT] statement that is followed by
the special ON CONFLICT clause shown above.

<p>The syntax that occurs in between the "ON CONFLICT" and "DO" keywords
is called the "conflict target".  The conflict target specifies a specific
uniqueness constraint that will trigger the upsert.  The conflict target
is required for DO UPDATE upserts, but is optional for DO NOTHING.
A DO NOTHING upsert without a conflict target works the same as an
[ON CONFLICT|INSERT OR IGNORE].

<p>If the insert operation would cause the uniqueness constraint identified
by the conflict-target clause to fail, then the insert is omitted and
either the DO NOTHING or DO UPDATE operation is performed instead.
In the case of a multi-row insert, this decision is made separately
for each row of the insert.








<p>Column names in the expressions of a DO UPDATE refer to the original
unchanged value of the column, before the attempted INSERT.  To use the
value that would have been inserted had the constraint not failed,
add the special "excluded." table qualifier to the column name.

<p>Some examples will help illustrate the difference:







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<p>An UPSERT is an ordinary [INSERT] statement that is followed by
the special ON CONFLICT clause shown above.

<p>The syntax that occurs in between the "ON CONFLICT" and "DO" keywords
is called the "conflict target".  The conflict target specifies a specific
uniqueness constraint that will trigger the upsert.  The conflict target
is required for DO UPDATE upserts, but is optional for DO NOTHING.  When
the conflict target is omitted, the upsert behavior is triggered by a
violation of any uniqueness constraint on the table of the INSERT.

<p>If the insert operation would cause the uniqueness constraint identified
by the conflict-target clause to fail, then the insert is omitted and
either the DO NOTHING or DO UPDATE operation is performed instead.
In the case of a multi-row insert, this decision is made separately
for each row of the insert.

<p>The special UPSERT processing happens only for uniqueness constraint on
the table that is receiving the INSERT. A "uniqueness constraint"
is an explicit UNIQUE or PRIMARY KEY constraint within
the CREATE TABLE statement, or a [unique index].
UPSERT does not intervene for failed NOT NULL or foreign key constraints
or for constraints that are implemented using triggers.

<p>Column names in the expressions of a DO UPDATE refer to the original
unchanged value of the column, before the attempted INSERT.  To use the
value that would have been inserted had the constraint not failed,
add the special "excluded." table qualifier to the column name.

<p>Some examples will help illustrate the difference: