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Overview
Comment:Corrects to comments on the STAT4 implementation.
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SHA1: e06f74d32d44f281dd21908d401184f35f9455a4
User & Date: drh 2013-10-14 14:21:59.159
Context
2013-10-14
14:30
Update the foreign_key_check pragma so that when a parent table is undefined it is treated as an empty table. (check-in: 208b259ad7 user: drh tags: trunk)
14:21
Corrects to comments on the STAT4 implementation. (check-in: e06f74d32d user: drh tags: trunk)
13:21
Make subroutines sampleCopy() and valueFromExpr() have file scope. (check-in: 1660efbe46 user: drh tags: trunk)
Changes
Unified Diff Ignore Whitespace Patch
Changes to src/analyze.c.
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** is between 3.6.18 and 3.7.8, inclusive, and unless SQLite is compiled
** with SQLITE_ENABLE_STAT2.  The sqlite_stat2 table is deprecated.
** The sqlite_stat2 table is superseded by sqlite_stat3, which is only
** created and used by SQLite versions 3.7.9 and later and with
** SQLITE_ENABLE_STAT3 defined.  The functionality of sqlite_stat3
** is a superset of sqlite_stat2.  The sqlite_stat4 is an enhanced
** version of sqlite_stat3 and is only available when compiled with
** SQLITE_ENABLE_STAT4 and in SQLite versions 3.8.0 and later.  It is
** not possible to enable both STAT3 and STAT4 at the same time.  If they
** are both enabled, then STAT4 takes precedence.
**
** For most applications, sqlite_stat1 provides all the statisics required
** for the query planner to make good choices.
**
** Format of sqlite_stat1:








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** is between 3.6.18 and 3.7.8, inclusive, and unless SQLite is compiled
** with SQLITE_ENABLE_STAT2.  The sqlite_stat2 table is deprecated.
** The sqlite_stat2 table is superseded by sqlite_stat3, which is only
** created and used by SQLite versions 3.7.9 and later and with
** SQLITE_ENABLE_STAT3 defined.  The functionality of sqlite_stat3
** is a superset of sqlite_stat2.  The sqlite_stat4 is an enhanced
** version of sqlite_stat3 and is only available when compiled with
** SQLITE_ENABLE_STAT4 and in SQLite versions 3.8.1 and later.  It is
** not possible to enable both STAT3 and STAT4 at the same time.  If they
** are both enabled, then STAT4 takes precedence.
**
** For most applications, sqlite_stat1 provides all the statisics required
** for the query planner to make good choices.
**
** Format of sqlite_stat1:
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** that indexed columns are compared against in the WHERE clauses of
** queries.
**
** The sqlite_stat4 table contains multiple entries for each index.
** The idx column names the index and the tbl column is the table of the
** index.  If the idx and tbl columns are the same, then the sample is
** of the INTEGER PRIMARY KEY.  The sample column is a blob which is the
** binary encoding of a key from the index, with the trailing rowid
** omitted.  The nEq column is a list of integers.  The first integer
** is the approximate number of entries in the index whose left-most 
** column exactly matches the left-most column of the sample.  The second
** integer in nEq is the approximate number of entries in the index where
** the first two columns match the first two columns of the sample.
** And so forth.  nLt is another list of integers that show the approximate
** number of entries that are strictly less than the sample.  The first
** integer in nLt contains the number of entries in the index where the
** left-most column is less than the left-most column of the sample.
** The K-th integer in the nLt entry is the number of index entries 
** where the first K columns are less than the first K columns of the
** sample.  The nDLt column is like nLt except that it contains the 








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** that indexed columns are compared against in the WHERE clauses of
** queries.
**
** The sqlite_stat4 table contains multiple entries for each index.
** The idx column names the index and the tbl column is the table of the
** index.  If the idx and tbl columns are the same, then the sample is
** of the INTEGER PRIMARY KEY.  The sample column is a blob which is the
** binary encoding of a key from the index.  The nEq column is a
** list of integers.  The first integer is the approximate number
** of entries in the index whose left-most column exactly matches
** the left-most column of the sample.  The second integer in nEq
** is the approximate number of entries in the index where the
** first two columns match the first two columns of the sample.
** And so forth.  nLt is another list of integers that show the approximate
** number of entries that are strictly less than the sample.  The first
** integer in nLt contains the number of entries in the index where the
** left-most column is less than the left-most column of the sample.
** The K-th integer in the nLt entry is the number of index entries 
** where the first K columns are less than the first K columns of the
** sample.  The nDLt column is like nLt except that it contains the
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