Fixed bug #27954.

This bug affects multi-row INSERT ... ON DUPLICATE into table
with PRIMARY KEY of AUTO_INCREMENT field and some additional UNIQUE indices.
If the first row in multi-row INSERT contains duplicated values of UNIQUE
indices, then following rows of multi-row INSERT (with either duplicated or
unique key field values) may me applied to _arbitrary_ records of table as
updates.
This bug was introduced in 5.0. Related code was widely rewritten in 5.1, and
5.1 is already free of this problem. 4.1 was not affected too.

When updating the row during INSERT ON DUPLICATE KEY UPDATE, we called
restore_auto_increment(), which set next_insert_id back to 0, but we
forgot to set clear_next_insert_id back to 0.
restore_auto_increment() function has been fixed.

mysql-test/r/insert_update.result

@@ -336,3 +336,25 @@ id	f1
 0	test1
 DROP TABLE t1;
 SET SQL_MODE='';
+CREATE TABLE t1 (
+id INT AUTO_INCREMENT PRIMARY KEY,
+c1 CHAR(1) UNIQUE KEY,
+cnt INT DEFAULT 1
+);
+INSERT INTO t1 (c1) VALUES ('A'), ('B'), ('C');
+SELECT * FROM t1;
+id	c1	cnt
+1	A	1
+2	B	1
+3	C	1
+INSERT  INTO t1 (c1) VALUES ('A'), ('X'), ('Y'), ('Z')
+ON DUPLICATE KEY UPDATE cnt=cnt+1;
+SELECT * FROM t1;
+id	c1	cnt
+1	A	2
+2	B	1
+3	C	1
+4	X	1
+5	Y	1
+6	Z	1
+DROP TABLE t1;

mysql-test/t/insert_update.test

@@ -247,3 +247,20 @@ REPLACE INTO t1 VALUES (0,"test1",null);
 SELECT id, f1 FROM t1;
 DROP TABLE t1;
 SET SQL_MODE='';
+
+#
+# Bug#27954: multi-row INSERT ... ON DUPLICATE with duplicated
+# row at the first place into table with AUTO_INCREMENT and
+# additional UNIQUE key.
+#
+CREATE TABLE t1 (
+  id INT AUTO_INCREMENT PRIMARY KEY,
+  c1 CHAR(1) UNIQUE KEY,
+  cnt INT DEFAULT 1
+);
+INSERT INTO t1 (c1) VALUES ('A'), ('B'), ('C');
+SELECT * FROM t1;
+INSERT  INTO t1 (c1) VALUES ('A'), ('X'), ('Y'), ('Z')
+  ON DUPLICATE KEY UPDATE cnt=cnt+1;
+SELECT * FROM t1;
+DROP TABLE t1;

sql/handler.cc

@@ -1685,7 +1685,14 @@ void handler::restore_auto_increment()
 {
   THD *thd= table->in_use;
   if (thd->next_insert_id)
+  {
     thd->next_insert_id= thd->prev_insert_id;
+    if (thd->next_insert_id == 0)
+    {
+      /* we didn't generate a value, engine will be called again */
+      thd->clear_next_insert_id= 0;
+    }
+  }
 }
 
 

sql/sql_class.h

@@ -1431,6 +1431,10 @@ public:
   */
   bool       insert_id_used;
 
+  /* 
+    clear_next_insert_id is set if engine was called at least once
+    for this statement to generate auto_increment value.
+  */
   bool       clear_next_insert_id;
   /* for IS NULL => = last_insert_id() fix in remove_eq_conds() */
   bool       substitute_null_with_insert_id;