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Overview
| Comment: | Another fix in the IN-operator algorithm description. |
|---|---|
| Downloads: | Tarball | ZIP archive | SQL archive |
| Timelines: | family | ancestors | descendants | both | rowvalue |
| Files: | files | file ages | folders |
| SHA1: |
f474aeac4fa62d87e73189868d7c7a29 |
| User & Date: | drh 2016-08-25 17:47:36 |
Context
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2016-08-25
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| 21:14 | Refactor the sqlite3ExprCodeIN() routine for improved maintainability. check-in: b56705ae user: drh tags: rowvalue | |
| 17:47 | Another fix in the IN-operator algorithm description. check-in: f474aeac user: drh tags: rowvalue | |
| 17:40 | Further refinement of the in-operator.md documentation. check-in: df064837 user: drh tags: rowvalue | |
Changes
Changes to src/in-operator.md.
73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 |
x=y1 OR x=y2
This is the INDEX_NOOP optimization and is only undertaken if the
IN operator is used for membership testing. If the IN operator is
driving a loop, then skip this step entirely.
2. Check the LHS to see if it is a partial-NULL and if it is, jump
ahead to step 4.
3. Do a binary search for the RHS using the LHS as a probe. If
an exact match is found, return TRUE.
4. If we do not need to distingish between FALSE and NULL,
then return FALSE.
5. If the RHS is non-NULL then return FALSE.
6. For each row in the RHS, compare that row against the LHS and
if the result is NULL, immediately return NULL. In the case
of a scalar IN operator, we only need to look at the very first
row the RHS because for a scalar RHS, all NULLs will always come
first. If the RHS is empty, this step is a no-op.
7. Return FALSE.
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| | < | > | | |
73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 |
x=y1 OR x=y2
This is the INDEX_NOOP optimization and is only undertaken if the
IN operator is used for membership testing. If the IN operator is
driving a loop, then skip this step entirely.
2. Check the LHS to see if it is a partial-NULL and if it is, jump
ahead to step 5.
3. Do a binary search of the RHS using the LHS as a probe. If
an exact match is found, return TRUE.
4. If the RHS is non-NULL then return FALSE.
5. If we do not need to distingish between FALSE and NULL,
then return FALSE.
6. For each row in the RHS, compare that row against the LHS and
if the result is NULL, immediately return NULL. In the case
of a scalar IN operator, we only need to look at the very first
row the RHS because for a scalar RHS, all NULLs will always come
first. If the RHS is empty, this step is a no-op.
7. Return FALSE.
|