160 lines
5.9 KiB
HTML
160 lines
5.9 KiB
HTML
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<!-- keywords: SQLITE_SCANSTAT_EST SQLITE_SCANSTAT_EXPLAIN SQLITE_SCANSTAT_NAME SQLITE_SCANSTAT_NLOOP SQLITE_SCANSTAT_NVISIT SQLITE_SCANSTAT_SELECTID {scanstatus options} -->
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<a href="intro.html"><h2>SQLite C Interface</h2></a>
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<h2>Prepared Statement Scan Status Opcodes</h2>
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</div>
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<blockquote><pre>
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#define SQLITE_SCANSTAT_NLOOP 0
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#define SQLITE_SCANSTAT_NVISIT 1
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#define SQLITE_SCANSTAT_EST 2
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#define SQLITE_SCANSTAT_NAME 3
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#define SQLITE_SCANSTAT_EXPLAIN 4
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#define SQLITE_SCANSTAT_SELECTID 5
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</pre></blockquote>
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<p>
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The following constants can be used for the T parameter to the
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<a href="../c3ref/stmt_scanstatus.html">sqlite3_stmt_scanstatus(S,X,T,V)</a> interface. Each constant designates a
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different metric for sqlite3_stmt_scanstatus() to return.</p>
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<p>When the value returned to V is a string, space to hold that string is
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managed by the prepared statement S and will be automatically freed when
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S is finalized.</p>
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<p><dl>
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<a name="sqlitescanstatnloop"></a>
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<dt>SQLITE_SCANSTAT_NLOOP</dt>
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<dd>The <a href="../c3ref/int64.html">sqlite3_int64</a> variable pointed to by the V parameter will be
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set to the total number of times that the X-th loop has run.</dd></p>
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<p><a name="sqlitescanstatnvisit"></a>
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<dt>SQLITE_SCANSTAT_NVISIT</dt>
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<dd>The <a href="../c3ref/int64.html">sqlite3_int64</a> variable pointed to by the V parameter will be set
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to the total number of rows examined by all iterations of the X-th loop.</dd></p>
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<p><a name="sqlitescanstatest"></a>
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<dt>SQLITE_SCANSTAT_EST</dt>
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<dd>The "double" variable pointed to by the V parameter will be set to the
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query planner's estimate for the average number of rows output from each
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iteration of the X-th loop. If the query planner's estimates was accurate,
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then this value will approximate the quotient NVISIT/NLOOP and the
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product of this value for all prior loops with the same SELECTID will
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be the NLOOP value for the current loop.</p>
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<p><a name="sqlitescanstatname"></a>
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<dt>SQLITE_SCANSTAT_NAME</dt>
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<dd>The "const char *" variable pointed to by the V parameter will be set
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to a zero-terminated UTF-8 string containing the name of the index or table
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used for the X-th loop.</p>
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<p><a name="sqlitescanstatexplain"></a>
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<dt>SQLITE_SCANSTAT_EXPLAIN</dt>
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<dd>The "const char *" variable pointed to by the V parameter will be set
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to a zero-terminated UTF-8 string containing the <a href="../eqp.html">EXPLAIN QUERY PLAN</a>
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description for the X-th loop.</p>
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<p><a name="sqlitescanstatselectid"></a>
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<dt>SQLITE_SCANSTAT_SELECT</dt>
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<dd>The "int" variable pointed to by the V parameter will be set to the
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"select-id" for the X-th loop. The select-id identifies which query or
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subquery the loop is part of. The main query has a select-id of zero.
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The select-id is the same value as is output in the first column
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of an <a href="../eqp.html">EXPLAIN QUERY PLAN</a> query.
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</dl>
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</p><p>See also lists of
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<a href="objlist.html">Objects</a>,
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<a href="constlist.html">Constants</a>, and
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<a href="funclist.html">Functions</a>.</p>
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