[wp-trac] [WordPress Trac] #32763: SQL query results depend on the number of blanks in query (due to error from "wpdb->get_table_from_query")

[WordPress Trac]

#32763: SQL query results depend on the number of blanks in query (due to error
from "wpdb->get_table_from_query")
--------------------------+-----------------------------
 Reporter:  klaus-b       |      Owner:
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  Database      |    Version:  4.2.2
 Severity:  normal        |   Keywords:
  Focuses:                |
--------------------------+-----------------------------
 A (non ASCII) query of form

 {{{
   SELECT <long fieldlist> from
     (SELECT <complex subquery>) as sq1
     LEFT JOIN
     (SELECT <simple subquery>) as sq2
 }}}

 didnt deliver a result tough some was expected.

 Modifying the query to:

 {{{
   SELECT <1000 spaces> <long fieldlist> from
     (SELECT <complex subquery>) as sq1
     LEFT JOIN
     (SELECT <simple subquery>) as sq2
 }}}

 Fixed the problem.

 I tracked it down to '''wpdb->get_table_from_query'''.
 * In first case (for reasons I didn't investigate on)
 '''wpdb->get_table_from_query''' returns '''"SELECT"'''
 * In second case (for reasons mentioned below)
 '''wpdb->get_table_from_query''' returns '''FALSE'''

 A reason for the different results is that
 '''wpdb->get_table_from_query''' only works on the first 1000 characters
 of the '''$query'''. Statement 3 of '''wpdb->get_table_from_query''':

 {{{
 $query = preg_replace( '/\((?!\s*select)[^(]*?\)/is', '()', substr(
 $query, 0, 1000 ) );
 }}}

 But this (of course) doesn't fix the problem. The correct query result is
 delivered in case 2 when '''wpdb->get_table_from_query''' due to enough
 blanks gives up (returning '''FALSE''') instead of delivering a wrong
 result '''"SELECT"''' as in case 1.

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Ticket URL: <https://core.trac.wordpress.org/ticket/32763>
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