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Overview
| Comment: | Comment enhancement to better explain the logic in the "x IS NULL" optimization. |
|---|---|
| Downloads: | Tarball | ZIP archive | SQL archive |
| Timelines: | family | ancestors | descendants | both | trunk |
| Files: | files | file ages | folders |
| SHA1: |
869f894798a65f8bc0e0b083866a784f |
| User & Date: | drh 2011-03-17 01:58:21 |
Context
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2011-03-17
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| 16:45 | Update the implementation of ".testctrl" in the command-line shell to use a look-up table rather than a long sequence of if-elses. Shorten source code lines of shell.c to 80 characters or less. check-in: 54bacb95 user: drh tags: trunk | |
| 01:58 | Comment enhancement to better explain the logic in the "x IS NULL" optimization. check-in: 869f8947 user: drh tags: trunk | |
| 01:34 | Enhances to the query planner such that "x IS NULL" constraints take the STAT2 statistics into account, just like "x=VALUE" constraints. check-in: 23531768 user: drh tags: trunk | |
Changes
Changes to src/where.c.
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#ifdef SQLITE_ENABLE_STAT2 /* ** Estimate the number of rows that will be returned based on ** an equality constraint x=VALUE and where that VALUE occurs in ** the histogram data. This only works when x is the left-most ** column of an index and sqlite_stat2 histogram data is available ** for that index. ** ** Write the estimated row count into *pnRow and return SQLITE_OK. ** If unable to make an estimate, leave *pnRow unchanged and return ** non-zero. ** ** This routine can fail if it is unable to load a collating sequence ** required for string comparison, or if unable to allocate memory |
| > |
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#ifdef SQLITE_ENABLE_STAT2 /* ** Estimate the number of rows that will be returned based on ** an equality constraint x=VALUE and where that VALUE occurs in ** the histogram data. This only works when x is the left-most ** column of an index and sqlite_stat2 histogram data is available ** for that index. When pExpr==NULL that means the constraint is ** "x IS NULL" instead of "x=VALUE". ** ** Write the estimated row count into *pnRow and return SQLITE_OK. ** If unable to make an estimate, leave *pnRow unchanged and return ** non-zero. ** ** This routine can fail if it is unable to load a collating sequence ** required for string comparison, or if unable to allocate memory |