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Overview
| Comment: | More fixes to the virtual table documentation. |
|---|---|
| Timelines: | family | ancestors | descendants | both | trunk |
| Files: | files | file ages | folders |
| SHA3-256: |
70c4eaad4d2748d788dcd8f5870af441 |
| User & Date: | drh 2018-11-16 14:33:01 |
Context
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2018-11-16
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| 14:35 | Add the SQLITE_CONSTRAINT return from xBestIndex to the change log. check-in: 14b1451274 user: drh tags: trunk | |
| 14:33 | More fixes to the virtual table documentation. check-in: 70c4eaad4d user: drh tags: trunk | |
| 14:30 | Explain the use of SQLITE_CONSTRAINT as a return value from xBestIndex. check-in: 52c277f049 user: drh tags: trunk | |
Changes
Changes to pages/vtab.in.
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<li><p>Scan all rows of tablevalued func and for each row find rows in realtab where x is equal to tablevaluedfunc.param1. </ol> <p>The xBestIndex method will be invoked once for each of the potential plans above. For plan 1, the aConstraint[].usable flag for for the SQLITE_CONSTRAINT_EQ constraint on the param1 column will be true because the right-hand side value for the "param1 = ?" constraint will be known. But for plan 2, the aConstraint[].usable flag for "param1 = ?" will be false because the right-hand side value is determined by an inner loop. Hence, the xBestIndex method should return SQLITE_CONSTRAINT when presented with plan 2, forcing SQLite to choose plan 1. <tcl>hd_fragment xdisconnect {sqlite3_module.xDisconnect} {xDisconnect}</tcl> <h2>The xDisconnect Method</h2> <codeblock> int (*xDisconnect)(sqlite3_vtab *pVTab); </codeblock> |
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<li><p>Scan all rows of tablevalued func and for each row find rows in realtab where x is equal to tablevaluedfunc.param1. </ol> <p>The xBestIndex method will be invoked once for each of the potential plans above. For plan 1, the aConstraint[].usable flag for for the SQLITE_CONSTRAINT_EQ constraint on the param1 column will be true because the right-hand side value for the "param1 = ?" constraint will be known, since it is determined by the outer realtab loop. But for plan 2, the aConstraint[].usable flag for "param1 = ?" will be false because the right-hand side value is determined by an inner loop and is thus an unknown quantity. Because param1 is a required input to the table-valued functions, the xBestIndex method should return SQLITE_CONSTRAINT when presented with plan 2, indicating that a required input is missing. This forces the query planner to select plan 1. <tcl>hd_fragment xdisconnect {sqlite3_module.xDisconnect} {xDisconnect}</tcl> <h2>The xDisconnect Method</h2> <codeblock> int (*xDisconnect)(sqlite3_vtab *pVTab); </codeblock> |