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Overview
| Comment: | Back out the previous change. We are instead going to modify the code to match the documentation. |
|---|---|
| Timelines: | family | ancestors | descendants | both | branch-3.29 |
| Files: | files | file ages | folders |
| SHA3-256: |
3578d6c47bfbf7a5c6149ae67a78d3db |
| User & Date: | drh 2019-08-05 20:39:49 |
Context
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2019-08-06
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| 17:02 | Improved documentation on how EXPLAIN only affects run-time but some PRAGMA statements operate at prepare-time and are thus unaffected by EXPLAIN. check-in: e167521765 user: drh tags: branch-3.29 | |
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2019-08-05
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| 20:39 | Back out the previous change. We are instead going to modify the code to match the documentation. check-in: 3578d6c47b user: drh tags: branch-3.29 | |
| 20:39 | Back out the previous change. We are instead going to modify the code to match the documentation. check-in: e16ada80d6 user: drh tags: trunk | |
| 12:55 | Update the documentation on the affinity of the columns of VIEWs and subqueries that are generated from expressions to match the actual implementation of 10 years standing - namely such columns have BLOB affinity, not no affinity. Ticket https://www.sqlite.org/src/info/d52a29a9e6bc55c5 check-in: 16a418966a user: drh tags: branch-3.29 | |
Changes
Changes to pages/datatype3.in.
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<li><p>^Otherwise, an expression has no affinity.
</ul>
<tcl>hd_fragment affview {rules for determining column affinity in VIEWs}</tcl>
<h2>Column Affinity For Views And Subqueries</h2>
<p>The columns of a [VIEW] or FROM-clause subquery have the same affinity
as the expressions in the result set of the [SELECT] statement that implements the VIEW
or subquery. Except, column of a VIEW or subquery that are generated by expressions
that have no affinity are assigned an affinity of BLOB.
Consider an example:
<blockquote><pre>
CREATE TABLE t1(a INT, b TEXT, c REAL);
CREATE VIEW v1(x,y,z) AS SELECT b, a+c, 42 FROM t1 WHERE b!=11;
</pre></blockquote>
<p>The affinity of the v1.x column will be the same as the affinity
of t1.b (TEXT), since v1.x maps directly into t1.b. But
columns v1.y and v1.z both have no affinity, since those columns
map into expression a+c and 42, and expressions always have no
affinity, so that v1.y and v1.z columns have an affinity of BLOB.
<p>When the [SELECT] statement that implements a [VIEW] or
FROM-clause subquery is a [compound SELECT] then the affinity of
each supposed column of the VIEW or subquery will
be the affinity of the corresponding result column for
one of the individual SELECT statements that make up
the compound.
|
| > | < | > | |
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<li><p>^Otherwise, an expression has no affinity.
</ul>
<tcl>hd_fragment affview {rules for determining column affinity in VIEWs}</tcl>
<h2>Column Affinity For Views And Subqueries</h2>
<p>The "columns" of a [VIEW] or FROM-clause subquery are really
the expressions
in the result set of the [SELECT] statement that implements the VIEW
or subquery. Thus, the affinity for columns of a VIEW or subquery
are determined by the expression affinity rules above.
Consider an example:
<blockquote><pre>
CREATE TABLE t1(a INT, b TEXT, c REAL);
CREATE VIEW v1(x,y,z) AS SELECT b, a+c, 42 FROM t1 WHERE b!=11;
</pre></blockquote>
<p>The affinity of the v1.x column will be the same as the affinity
of t1.b (TEXT), since v1.x maps directly into t1.b. But
columns v1.y and v1.z both have no affinity, since those columns
map into expression a+c and 42, and expressions always have no
affinity.
<p>When the [SELECT] statement that implements a [VIEW] or
FROM-clause subquery is a [compound SELECT] then the affinity of
each supposed column of the VIEW or subquery will
be the affinity of the corresponding result column for
one of the individual SELECT statements that make up
the compound.
|