217 lines
8.5 KiB
HTML
217 lines
8.5 KiB
HTML
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The ON CONFLICT Clause
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</div>
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<p><b><a href="syntax/conflict-clause.html">conflict-clause:</a></b>
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<img alt="syntax diagram conflict-clause" src="images/syntax/conflict-clause.gif" />
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</div>
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<p>The ON CONFLICT clause is a
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non-standard extension specific to SQLite
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that can appear in many other SQL commands.
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It is given its own section in this document because it is not
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part of standard SQL and therefore might not be familiar.</p>
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<p>The ON CONFLICT clause described here has been a part of
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SQLite since before version 3.0.0 (2004-06-18). The phrase
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"ON CONFLICT" is also part of <a href="lang_upsert.html">UPSERT</a>, which is an extension
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to <a href="lang_insert.html">INSERT</a> added in version 3.24.0 (2018-06-04). Do not
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confuse these two separate uses of the "ON CONFLICT" phrase.
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</p><p>The syntax for the ON CONFLICT clause is as shown above for
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the CREATE TABLE command. For the INSERT and
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UPDATE commands, the keywords "ON CONFLICT" are replaced by "OR" so that
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the syntax reads more naturally. For example, instead of
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"INSERT ON CONFLICT IGNORE" we have "INSERT OR IGNORE".
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The keywords change but the meaning of the clause is the same
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either way.</p>
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<p>The ON CONFLICT clause applies to <a href="lang_createtable.html#uniqueconst">UNIQUE</a>, <a href="lang_createtable.html#notnullconst">NOT NULL</a>,
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<a href="lang_createtable.html#ckconst">CHECK</a>, and <a href="lang_createtable.html#primkeyconst">PRIMARY KEY</a> constraints.
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The ON CONFLICT algorithm does not
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apply to <a href="foreignkeys.html">FOREIGN KEY constraints</a>.
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There are five conflict resolution algorithm choices:
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ROLLBACK, ABORT, FAIL, IGNORE, and REPLACE.
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The default conflict resolution algorithm is ABORT. This
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is what they mean:</p>
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<dl>
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<dt><b>ROLLBACK</b></dt>
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<dd><p> When an applicable constraint violation occurs, the ROLLBACK
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resolution algorithm aborts the current SQL statement with
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an SQLITE_CONSTRAINT error and rolls back the current transaction.
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If no transaction is
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active (other than the implied transaction that is created on every
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command) then the ROLLBACK resolution algorithm works the same as the
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ABORT algorithm.</p></dd>
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<dt><b>ABORT</b></dt>
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<dd><p> When an applicable constraint violation occurs, the ABORT
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resolution algorithm aborts the current SQL statement
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with an SQLITE_CONSTRAINT error and backs out any changes
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made by the current SQL statement; but changes caused
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by prior SQL statements within the same transaction are preserved and the
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transaction remains active.
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This is the default behavior and the behavior specified by the SQL
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standard.</p></dd>
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<dt><b>FAIL</b></dt>
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<dd><p> When an applicable constraint violation occurs, the FAIL
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resolution algorithm aborts the current SQL statement with an
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SQLITE_CONSTRAINT error. But the FAIL resolution does not
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back out prior changes of the SQL statement that failed nor does
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it end the transaction.
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For example, if an UPDATE
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statement encountered a constraint violation on the 100th row that
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it attempts to update, then the first 99 row changes are preserved
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but changes to rows 100 and beyond never occur.</p>
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<p>The FAIL behavior only works for uniqueness, NOT NULL, and CHECK
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constraints. A <a href="foreignkeys.html">foreign key constraint</a> violation causes an ABORT.
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</p></dd>
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<dt><b>IGNORE</b></dt>
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<dd><p> When an applicable constraint violation occurs,
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the IGNORE resolution algorithm skips the one row that contains
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the constraint violation and continues processing subsequent rows
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of the SQL statement as if nothing went wrong.
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Other rows before and after the row that
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contained the constraint violation are inserted or updated
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normally. No error is returned for uniqueness, NOT NULL, and
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UNIQUE constraint errors when the IGNORE conflict resolution
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algorithm is used. However, the IGNORE conflict resolution
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algorithm works like ABORT for <a href="foreignkeys.html">foreign key constraint</a> errors.
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</p>
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</dd>
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<dt><b>REPLACE</b></dt>
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<dd><p> When a <a href="lang_createtable.html#uniqueconst">UNIQUE</a> or <a href="lang_createtable.html#primkeyconst">PRIMARY KEY</a> constraint violation occurs,
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the REPLACE algorithm
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deletes pre-existing rows that are causing the constraint violation
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prior to inserting or updating the current row and the command continues
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executing normally.
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If a <a href="lang_createtable.html#notnullconst">NOT NULL</a> constraint violation occurs, the REPLACE conflict
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resolution replaces the NULL value with
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the default value for that column, or if the column has no default
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value, then the ABORT algorithm is used.
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If a <a href="lang_createtable.html#ckconst">CHECK constraint</a> or <a href="foreignkeys.html">foreign key constraint</a> violation occurs,
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the REPLACE conflict resolution algorithm works like ABORT.</p>
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<p>When the REPLACE conflict resolution strategy deletes rows in order to
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satisfy a constraint, <a href="lang_createtrigger.html">delete triggers</a> fire if and only if
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<a href="pragma.html#pragma_recursive_triggers">recursive triggers</a> are enabled.</p>
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<p>The <a href="c3ref/update_hook.html">update hook</a> is not invoked for rows that
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are deleted by the REPLACE conflict resolution strategy. Nor does
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REPLACE increment the <a href="c3ref/changes.html">change counter</a>.
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The exceptional behaviors defined in this paragraph might change
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in a future release.</p>
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</dd></dl>
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<p>The algorithm specified in the OR clause of an INSERT or UPDATE
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overrides any algorithm specified in a CREATE TABLE.
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If no algorithm is specified anywhere, the ABORT algorithm is used.</p>
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