Fix for bug #42957: no results from

select where .. (col=col and col=col) or ... (false expression)

Problem: optimizer didn't take into account a singular case 
when we eliminated all the predicates at the AND level of WHERE.
That may lead to wrong results.

Fix: replace (a=a AND a=a...) with TRUE if we eliminated all the
predicates.


mysql-test/r/select.result:
  Fix for bug #42957: no results from 
  select where .. (col=col and col=col) or ... (false expression)
    - test result.
mysql-test/t/select.test:
  Fix for bug #42957: no results from 
  select where .. (col=col and col=col) or ... (false expression)
    - test case.
sql/sql_select.cc:
  Fix for bug #42957: no results from 
  select where .. (col=col and col=col) or ... (false expression)
    - replacing equality predicates by multiple equality items check
  if we eliminate all the predicates at the AND level and 
  replace them with TRUE if so.

1 files changed, 16 insertions, 0 deletions

diff --git a/mysql-test/t/select.test b/mysql-test/t/select.test
index ccdb53ec11f..8981ddbe2e4 100644
--- a/mysql-test/t/select.test
+++ b/mysql-test/t/select.test
@@ -3769,4 +3769,20 @@ SELECT date_nokey FROM C
 
 DROP TABLE A,C;
 
+#
+# Bug #42957: no results from 
+# select where .. (col=col and col=col) or ... (false expression)
+#
+CREATE TABLE t1 (a INT NOT NULL, b INT);
+INSERT INTO t1 VALUES (1, 1);
+EXPLAIN EXTENDED SELECT * FROM t1 WHERE (a=a AND a=a) OR b > 2;
+SELECT * FROM t1 WHERE (a=a AND a=a) OR b > 2;
+DROP TABLE t1;
+
+CREATE TABLE t1 (a INT NOT NULL, b INT NOT NULL, c INT NOT NULL);
+EXPLAIN EXTENDED SELECT * FROM t1 WHERE (a=a AND b=b AND c=c) OR b > 20;
+EXPLAIN EXTENDED SELECT * FROM t1 WHERE (a=a AND a=a AND b=b) OR b > 20;
+EXPLAIN EXTENDED SELECT * FROM t1 WHERE (a=a AND b=b AND a=a) OR b > 20;
+DROP TABLE t1;
+
 --echo End of 5.1 tests