Join_tab_compare_default Class Reference

#include <sql_select.h>

List of all members.

Public Member Functions
bool	operator() (const JOIN_TAB *jt1, const JOIN_TAB *jt2)

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Detailed Description

"Less than" comparison function object used to compare two JOIN_TAB objects based on a number of factors in this order:

• table before another table that depends on it (straight join, outer join etc), then
• table before another table that depends on it to use a key as access method, then
• table with smallest number of records first, then
• the table with lowest-value pointer (i.e., the one located in the lowest memory address) first.

Parameters:

jt1	first JOIN_TAB object
jt2	second JOIN_TAB object

Note:

The order relation implemented by Join_tab_compare_default is not transitive, i.e. it is possible to choose a, b and c such that (a < b) && (b < c) but (c < a). This is the case in the following example:

a: dependent = <none> found_records = 3 b: dependent = <none> found_records = 4 c: dependent = b found_records = 2

a < b: because a has fewer records b < c: because c depends on b (e.g outer join dependency) c < a: because c has fewer records

This implies that the result of a sort using the relation implemented by Join_tab_compare_default () depends on the order in which elements are compared, i.e. the result is implementation-specific.

Returns:

true if jt1 is smaller than jt2, false otherwise

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The documentation for this class was generated from the following file:

• sql_select.h