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Overview
| Comment: | Add a requirement that CHECK constraints cannot contain subqueries. |
|---|---|
| Timelines: | family | ancestors | descendants | both | trunk |
| Files: | files | file ages | folders |
| SHA1: | 1f3d321253ced57c80992c6f898c144a24b87b69 |
| User & Date: | drh 2011-05-13 16:47:34 |
Context
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2011-05-18
| ||
| 13:14 | Add documentation for 8+3 filenames. check-in: 4e973ec4bf user: drh tags: trunk | |
|
2011-05-13
| ||
| 16:57 | Rather than document goofy behavior, better to make the behavior less goofy. (Was: Clarify in the documentation that last_insert_rowid() does not work for virtual tables.) Closed-Leaf check-in: f102116e8a user: drh tags: mistake | |
| 16:47 | Add a requirement that CHECK constraints cannot contain subqueries. check-in: 1f3d321253 user: drh tags: trunk | |
|
2011-05-11
| ||
| 20:53 | Improvements to capi3ref hyperlinking. check-in: b12665db54 user: drh tags: trunk | |
Changes
Changes to pages/lang.in.
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<li>^If a NOT NULL constraint is specified, then the column must have a
default value other than NULL.
<li>^If [foreign key constraints] are [foreign_keys pragma | enabled] and
a column with a [foreign-key-clause | REFERENCES clause]
is added, the column must have a default value of NULL.
</ul>
<p>^Note also that when adding a CHECK constraint, the CHECK constraint
is not tested against preexisting rows of the table.
^This can result in a table that contains data that
is in violation of the CHECK constraint. Future versions of SQLite might
change to validate CHECK constraints as they are added.</p>
<p> The execution time of the ALTER TABLE command is independent of
the amount of data in the table. The ALTER TABLE command runs as quickly
................................................................................
constraints are implemented by creating an index in the database (in the same
way as a [CREATE INDEX|"CREATE UNIQUE INDEX"] statement would). ^Such an
index is used like any other index in the database to [optimizer|optimize
queries]. As a result, there often no advantage (but significant overhead)
in creating an index on a set of columns that are already collectively
subject to a UNIQUE or PRIMARY KEY constraint.
<p>^(A <b>CHECK</b> constraint may be attached to a column definition or
specified as a table constraint. In practice it makes no difference.)^ ^(Each
time a new row is inserted into the table or an existing row is updated,
the expression associated with each CHECK constraint is evaluated and
cast to a NUMERIC value in the same way as a [CAST expression]. If the
result is zero (integer value 0 or real value 0.0), then a constraint
violation has occurred.)^ ^If the CHECK expression evaluates to NULL, or
any other non-zero value, it is not a constraint violation.
<p>CHECK constraints have been supported since [version 3.3.0]. Prior to
version 3.3.0, CHECK constraints were parsed but not enforced.
<p>^A <b>NOT NULL</b> constraint may only be attached to a column definition,
not specified as a table constraint. Not surprisingly, ^(a NOT NULL
constraint dictates that the associated column may not contain a NULL value.
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<li>^If a NOT NULL constraint is specified, then the column must have a
default value other than NULL.
<li>^If [foreign key constraints] are [foreign_keys pragma | enabled] and
a column with a [foreign-key-clause | REFERENCES clause]
is added, the column must have a default value of NULL.
</ul>
<p>^Note also that when adding a [CHECK constraint], the CHECK constraint
is not tested against preexisting rows of the table.
^This can result in a table that contains data that
is in violation of the CHECK constraint. Future versions of SQLite might
change to validate CHECK constraints as they are added.</p>
<p> The execution time of the ALTER TABLE command is independent of
the amount of data in the table. The ALTER TABLE command runs as quickly
................................................................................
constraints are implemented by creating an index in the database (in the same
way as a [CREATE INDEX|"CREATE UNIQUE INDEX"] statement would). ^Such an
index is used like any other index in the database to [optimizer|optimize
queries]. As a result, there often no advantage (but significant overhead)
in creating an index on a set of columns that are already collectively
subject to a UNIQUE or PRIMARY KEY constraint.
<tcl>hd_fragment {ckconst} {CHECK} {CHECK constraint} {CHECK constraints}</tcl>
<p>^(A <b>CHECK</b> constraint may be attached to a column definition or
specified as a table constraint. In practice it makes no difference.)^ ^(Each
time a new row is inserted into the table or an existing row is updated,
the expression associated with each CHECK constraint is evaluated and
cast to a NUMERIC value in the same way as a [CAST expression]. If the
result is zero (integer value 0 or real value 0.0), then a constraint
violation has occurred.)^ ^If the CHECK expression evaluates to NULL, or
any other non-zero value, it is not a constraint violation.
^The expression of a CHECK constraint may not contain a subquery.
<p>CHECK constraints have been supported since [version 3.3.0]. Prior to
version 3.3.0, CHECK constraints were parsed but not enforced.
<p>^A <b>NOT NULL</b> constraint may only be attached to a column definition,
not specified as a table constraint. Not surprisingly, ^(a NOT NULL
constraint dictates that the associated column may not contain a NULL value.
|