**
** ^The sqlite3_value objects that are passed as parameters into the
** implementation of [application-defined SQL functions] are protected.
+** ^The sqlite3_value objects returned by [sqlite3_vtab_rhs_value()]
+** are protected.
** ^The sqlite3_value object returned by
** [sqlite3_column_value()] is unprotected.
** Unprotected sqlite3_value objects may only be used as arguments
**
** These macros define the allowed values for the
** [sqlite3_index_info].aConstraint[].op field. Each value represents
-** an operator that is part of a constraint term in the wHERE clause of
+** an operator that is part of a constraint term in the WHERE clause of
** a query that uses a [virtual table].
-*/
-#define SQLITE_INDEX_CONSTRAINT_EQ 2
-#define SQLITE_INDEX_CONSTRAINT_GT 4
-#define SQLITE_INDEX_CONSTRAINT_LE 8
-#define SQLITE_INDEX_CONSTRAINT_LT 16
-#define SQLITE_INDEX_CONSTRAINT_GE 32
-#define SQLITE_INDEX_CONSTRAINT_MATCH 64
-#define SQLITE_INDEX_CONSTRAINT_LIKE 65
-#define SQLITE_INDEX_CONSTRAINT_GLOB 66
-#define SQLITE_INDEX_CONSTRAINT_REGEXP 67
-#define SQLITE_INDEX_CONSTRAINT_NE 68
-#define SQLITE_INDEX_CONSTRAINT_ISNOT 69
-#define SQLITE_INDEX_CONSTRAINT_ISNOTNULL 70
-#define SQLITE_INDEX_CONSTRAINT_ISNULL 71
-#define SQLITE_INDEX_CONSTRAINT_IS 72
-#define SQLITE_INDEX_CONSTRAINT_LIMIT 73
-#define SQLITE_INDEX_CONSTRAINT_OFFSET 74
-#define SQLITE_INDEX_CONSTRAINT_FUNCTION 150
+**
+** ^The left-hand operand of the operator is given by the corresponding
+** aConstraint[].iColumn field. ^An iColumn of -1 indicates the left-hand
+** operand is the rowid.
+** The SQLITE_INDEX_CONSTRAINT_LIMIT and SQLITE_INDEX_CONSTRAINT_OFFSET
+** operators have no left-hand operand, and so for those operators the
+** corresponding aConstraint[].iColumn is meaningless and should not be
+** used.
+**
+** All operator values from SQLITE_INDEX_CONSTRAINT_FUNCTION through
+** value 255 are reserved to represent functions that are overloaded
+** by the [xFindFunction|xFindFunction method] of the virtual table
+** implementation.
+**
+** The right-hand operands for each constraint might be accessible using
+** the [sqlite3_vtab_rhs_value()] interface. Usually the right-hand
+** operand is only available if it appears as a single constant literal
+** in the input SQL. If the right-hand operand is another column or an
+** expression (even a constant expression) or a parameter, then the
+** sqlite3_vtab_rhs_value() probably will not be able to extract it.
+** ^The SQLITE_INDEX_CONSTRAINT_ISNULL and
+** SQLITE_INDEX_CONSTRAINT_ISNOTNULL operators have no right-hand operand
+** and hence calls to sqlite3_vtab_rhs_value() for those operators will
+** always return SQLITE_NOTFOUND.
+**
+** The collating sequence to be used for comparison can be found using
+** the [sqlite3_vtab_collation()] interface. For most real-world virtual
+** tables, the collating sequence of constraints does not matter (for example
+** because the constraints are numeric) and so the sqlite3_vtab_collation()
+** interface is no commonly needed.
+*/
+#define SQLITE_INDEX_CONSTRAINT_EQ 2
+#define SQLITE_INDEX_CONSTRAINT_GT 4
+#define SQLITE_INDEX_CONSTRAINT_LE 8
+#define SQLITE_INDEX_CONSTRAINT_LT 16
+#define SQLITE_INDEX_CONSTRAINT_GE 32
+#define SQLITE_INDEX_CONSTRAINT_MATCH 64
+#define SQLITE_INDEX_CONSTRAINT_LIKE 65
+#define SQLITE_INDEX_CONSTRAINT_GLOB 66
+#define SQLITE_INDEX_CONSTRAINT_REGEXP 67
+#define SQLITE_INDEX_CONSTRAINT_NE 68
+#define SQLITE_INDEX_CONSTRAINT_ISNOT 69
+#define SQLITE_INDEX_CONSTRAINT_ISNOTNULL 70
+#define SQLITE_INDEX_CONSTRAINT_ISNULL 71
+#define SQLITE_INDEX_CONSTRAINT_IS 72
+#define SQLITE_INDEX_CONSTRAINT_LIMIT 73
+#define SQLITE_INDEX_CONSTRAINT_OFFSET 74
+#define SQLITE_INDEX_CONSTRAINT_FUNCTION 150
/*
** CAPI3REF: Register A Virtual Table Implementation
** CAPI3REF: Determine if a virtual table query is DISTINCT
** METHOD: sqlite3_index_info
**
-** This API may only be used from within an xBestIndex() callback. The
-** results of calling it from outside of an xBestIndex() callback are
-** undefined and probably harmful.
+** This API may only be used from within an [xBestIndex|xBestIndex method]
+** of a [virtual table] implementation. The result of calling this
+** interface from outside of xBestIndex() is undefined and probably harmful.
**
-** ^The sqlite3_vtab_distinct() returns an integer that is either 0, 1, or
-** 2. The integer returned by sqlite3_vtab_distinct() gives the virtual table
-** additional information about how the query planner wants the output to be
-** ordered. As long as the virtual table can meet the ordering requirements
-** of the query planner, it may set the "orderByConsumed" flag.
+** ^The sqlite3_vtab_distinct() interface returns an integer that is
+** either 0, 1, or 2. The integer returned by sqlite3_vtab_distinct()
+** gives the virtual table additional information about how the query
+** planner wants the output to be ordered. As long as the virtual table
+** can meet the ordering requirements of the query planner, it may set
+** the "orderByConsumed" flag.
**
** <ol><li value="0"><p>
** ^If the sqlite3_vtab_distinct() interface returns 0, that means
** [sqlite3_index_info] object. This is the default expectation. If the
** virtual table outputs all rows in sorted order, then it is always safe for
** the xBestIndex method to set the "orderByConsumed" flag, regardless of
-** what the return value from sqlite3_vtab_distinct().
+** the return value from sqlite3_vtab_distinct().
** <li value="1"><p>
** ^(If the sqlite3_vtab_distinct() interface returns 1, that means
** that the query planner does not need the rows to be returned in sorted order
** order, as long as rows with the same values in all "aOrderBy" columns
** are adjacent.)^ ^(Furthermore, only a single row for each particular
** combination of values in the columns identified by the "aOrderBy" field
-** needs to be returned.)^ ^It is ok always for two or more rows with the same
+** needs to be returned.)^ ^It is always ok for two or more rows with the same
** values in all "aOrderBy" columns to be returned, as long as all such rows
** are adjacent. ^The virtual table may, if it chooses, omit extra rows
** that have the same value for all columns identified by "aOrderBy".
** CAPI3REF: Constraint values in xBestIndex()
** METHOD: sqlite3_index_info
**
-** This API may only be used from within an xBestIndex() callback. The
-** results of calling it from outside of an xBestIndex() callback are
-** undefined and probably harmful.
+** This API may only be used from within the [xBestIndex|xBestIndex method]
+** of a [virtual table] implementation. The result of calling this interface
+** from outside of an xBestIndex method are undefined and probably harmful.
**
** ^When the sqlite3_vtab_rhs_value(P,J,V) interface is invoked from within
** the [xBestIndex] method of a [virtual table] implementation, with P being
** a copy of the [sqlite3_index_info] object pointer passed into xBestIndex and
** J being a 0-based index into P->aConstraint[], then this routine
-** attempts to set *V to be the value on the right-hand side of
-** that constraint if the right-hand side is a known constant. ^If the
-** right-hand side of the constraint is not known, then *V is set to a NULL
-** pointer. ^The sqlite3_vtab_rhs_value(P,J,V) interface returns SQLITE_OK if
+** attempts to set *V to the value of the right-hand operand of
+** that constraint if the right-hand operand is known. ^If the
+** right-hand operand is not known, then *V is set to a NULL pointer.
+** ^The sqlite3_vtab_rhs_value(P,J,V) interface returns SQLITE_OK if
** and only if *V is set to a value. ^The sqlite3_vtab_rhs_value(P,J,V)
** inteface returns SQLITE_NOTFOUND if the right-hand side of the J-th
** constraint is not available. ^The sqlite3_vtab_rhs_value() interface
** can return an result code other than SQLITE_OK or SQLITE_NOTFOUND if
** something goes wrong.
**
-** ^The sqlite3_value object returned in *V remains valid for the duration of
-** the xBestIndex method code. ^When xBestIndex returns, the sqlite3_value
-** object returned by sqlite3_vtab_rhs_value() is automatically deallocated.
+** The sqlite3_vtab_rhs_value() interface is usually only successful if
+** the right-hand operand of a constraint is a literal value in the original
+** SQL statement. If the right-hand operand is an expression or a reference
+** to some other column or a [host parameter], then sqlite3_vtab_rhs_value()
+** will probably return [SQLITE_NOTFOUND].
+**
+** ^(Some constraints, such as [SQLITE_INDEX_CONSTRAINT_ISNULL] and
+** [SQLITE_INDEX_CONSTRAINT_ISNOTNULL], have no right-hand operand. For such
+** constraints, sqlite3_vtab_rhs_value() always returns SQLITE_NOTFOUND.)^
+**
+** ^The [sqlite3_value] object returned in *V is a protected sqlite3_value
+** and remains valid for the duration of the xBestIndex method call.
+** ^When xBestIndex returns, the sqlite3_value object returned by
+** sqlite3_vtab_rhs_value() is automatically deallocated.
+**
+** The "_rhs_" in the name of this routine is an appreviation for
+** "Right-Hand Side".
*/
int sqlite3_vtab_rhs_value(sqlite3_index_info*, int, sqlite3_value **ppVal);
projects / thirdparty / sqlite.git / commitdiff
