Added function last_value() which returns the last value but evalutes all arguments as a side effect.

Original patch by Eric Herman

client/mysql.cc:
  Added LAST_VALUE
mysql-test/r/last_value.result:
  Testing of LAST_VALUE
mysql-test/t/last_value.test:
  Testing of LAST_VALUE
sql/item_func.cc:
  Added LAST_VALUE()
sql/item_func.h:
  Added LAST_VALUE()
sql/lex.h:
  Added LAST_VALUE()
sql/sql_yacc.yy:
  Added LAST_VALUE()

client/mysql.cc

@@ -897,6 +897,7 @@ static COMMANDS commands[] = {
   { "LAST_INSERT_ID", 0, 0, 0, ""},
   { "ISSIMPLE", 0, 0, 0, ""},
   { "LAST_DAY", 0, 0, 0, ""},
+  { "LAST_VALUE", 0, 0, 0, ""},
   { "LCASE", 0, 0, 0, ""},
   { "LEAST", 0, 0, 0, ""},
   { "LENGTH", 0, 0, 0, ""},

mysql-test/r/last_value.result

@@ -0,0 +1,73 @@
+drop table if exists t1;
+drop database if exists mysqltest;
+CREATE TABLE t1 (a INT, b INT, c INT, d INT);
+INSERT INTO t1 VALUES (1,3,0,NULL),(2,2,0,NULL),(3,4,0,NULL),(4,2,0,NULL);
+SELECT * FROM t1;
+a	b	c	d
+1	3	0	NULL
+2	2	0	NULL
+3	4	0	NULL
+4	2	0	NULL
+UPDATE t1 SET c=LAST_VALUE(@last_a:=a,@last_b:=b,@last_c:=c,1), d=4211 WHERE c=0 ORDER BY b DESC LIMIT 1;
+SELECT @last_a, @last_b, @last_c;
+@last_a	@last_b	@last_c
+3	4	0
+SELECT * FROM t1;
+a	b	c	d
+1	3	0	NULL
+2	2	0	NULL
+3	4	1	4211
+4	2	0	NULL
+DROP TABLE t1;
+SELECT LAST_VALUE(@last_a:=1,@last_b:=1);
+Catalog	Database	Table	Table_alias	Column	Column_alias	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
+def					LAST_VALUE(@last_a:=1,@last_b:=1)	8	1	1	N	32897	0	63
+LAST_VALUE(@last_a:=1,@last_b:=1)
+1
+select @last_b;
+Catalog	Database	Table	Table_alias	Column	Column_alias	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
+def					@last_b	8	20	1	Y	32896	0	63
+@last_b
+1
+SELECT LAST_VALUE(@last_a:=1,@last_b:=1.0);
+Catalog	Database	Table	Table_alias	Column	Column_alias	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
+def					LAST_VALUE(@last_a:=1,@last_b:=1.0)	246	4	3	N	32897	1	63
+LAST_VALUE(@last_a:=1,@last_b:=1.0)
+1.0
+select @last_b;
+Catalog	Database	Table	Table_alias	Column	Column_alias	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
+def					@last_b	246	83	3	Y	32896	30	63
+@last_b
+1.0
+SELECT LAST_VALUE(@last_a:=1,@last_b:="hello");
+Catalog	Database	Table	Table_alias	Column	Column_alias	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
+def					LAST_VALUE(@last_a:=1,@last_b:="hello")	253	5	5	N	1	31	8
+LAST_VALUE(@last_a:=1,@last_b:="hello")
+hello
+select @last_b;
+Catalog	Database	Table	Table_alias	Column	Column_alias	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
+def					@last_b	250	16777215	5	Y	0	31	8
+@last_b
+hello
+SELECT date(LAST_VALUE(@last_a:=1,@last_b:="2001-02-03"));
+Catalog	Database	Table	Table_alias	Column	Column_alias	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
+def					date(LAST_VALUE(@last_a:=1,@last_b:="2001-02-03"))	10	10	10	Y	128	0	63
+date(LAST_VALUE(@last_a:=1,@last_b:="2001-02-03"))
+2001-02-03
+select @last_b;
+Catalog	Database	Table	Table_alias	Column	Column_alias	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
+def					@last_b	250	16777215	10	Y	0	31	8
+@last_b
+2001-02-03
+SELECT LAST_VALUE(@last_a:=1,@last_b:="2001-02-03",NULL);
+Catalog	Database	Table	Table_alias	Column	Column_alias	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
+def					LAST_VALUE(@last_a:=1,@last_b:="2001-02-03",NULL)	6	0	0	Y	32896	0	63
+LAST_VALUE(@last_a:=1,@last_b:="2001-02-03",NULL)
+NULL
+select @last_b;
+Catalog	Database	Table	Table_alias	Column	Column_alias	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
+def					@last_b	250	16777215	10	Y	0	31	8
+@last_b
+2001-02-03
+SELECT LAST_VALUE();
+ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near ')' at line 1

mysql-test/t/last_value.test

@@ -0,0 +1,43 @@
+#
+# Tests for the LAST_VALUE function
+#
+
+--disable_warnings
+drop table if exists t1;
+drop database if exists mysqltest;
+--enable_warnings
+
+# CREATE TABLE `queue` (
+#  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
+#  `priority` int(11) DEFAULT NULL,
+#  `state` int(11) DEFAULT NULL,
+#  `pid` int(10) unsigned DEFAULT NULL,
+#  `dat` varbinary(200) DEFAULT NULL,
+#  PRIMARY KEY (`id`)
+# )
+
+CREATE TABLE t1 (a INT, b INT, c INT, d INT);
+INSERT INTO t1 VALUES (1,3,0,NULL),(2,2,0,NULL),(3,4,0,NULL),(4,2,0,NULL);
+SELECT * FROM t1;
+UPDATE t1 SET c=LAST_VALUE(@last_a:=a,@last_b:=b,@last_c:=c,1), d=4211 WHERE c=0 ORDER BY b DESC LIMIT 1;
+SELECT @last_a, @last_b, @last_c;
+SELECT * FROM t1;
+DROP TABLE t1;
+
+#
+# Test with different types
+#
+--enable_metadata
+SELECT LAST_VALUE(@last_a:=1,@last_b:=1);
+select @last_b;
+SELECT LAST_VALUE(@last_a:=1,@last_b:=1.0);
+select @last_b;
+SELECT LAST_VALUE(@last_a:=1,@last_b:="hello");
+select @last_b;
+SELECT date(LAST_VALUE(@last_a:=1,@last_b:="2001-02-03"));
+select @last_b;
+SELECT LAST_VALUE(@last_a:=1,@last_b:="2001-02-03",NULL);
+select @last_b;
+--disable_metadata
+--error ER_PARSE_ERROR
+SELECT LAST_VALUE();

sql/item_func.cc

@@ -6816,3 +6816,62 @@ longlong Item_func_uuid_short::val_int()
   mysql_mutex_unlock(&LOCK_short_uuid_generator);
   return (longlong) val;
 }
+
+
+/**
+  Last_value - return last argument.
+*/
+
+void Item_func_last_value::evaluate_sideeffects()
+{
+  DBUG_ASSERT(fixed == 1 && arg_count > 0);
+  for (uint i= 0; i < arg_count-1 ; i++)
+    args[i]->val_int();
+}
+
+String *Item_func_last_value::val_str(String *str)
+{
+  String *tmp;
+  evaluate_sideeffects();
+  tmp= last_value->val_str(str);
+  null_value= last_value->null_value;
+  return tmp;
+}
+
+longlong Item_func_last_value::val_int()
+{
+  longlong tmp;
+  evaluate_sideeffects();
+  tmp= last_value->val_int();
+  null_value= last_value->null_value;
+  return tmp;
+}
+
+double Item_func_last_value::val_real()
+{
+  double tmp;
+  evaluate_sideeffects();
+  tmp= last_value->val_real();
+  null_value= last_value->null_value;
+  return tmp;
+}
+
+my_decimal *Item_func_last_value::val_decimal(my_decimal *decimal_value)
+{
+  my_decimal *tmp;
+  evaluate_sideeffects();
+  tmp= last_value->val_decimal(decimal_value);
+  null_value= last_value->null_value;
+  return tmp;
+}
+
+
+void Item_func_last_value::fix_length_and_dec()
+{
+  last_value=          args[arg_count -1];
+  decimals=            last_value->decimals;
+  max_length=          last_value->max_length;
+  collation.set(last_value->collation.collation);
+  maybe_null=          last_value->maybe_null;
+  unsigned_flag=       last_value->unsigned_flag;
+}

sql/item_func.h

@@ -2003,6 +2003,27 @@ public:
   }
 };
 
+
+class Item_func_last_value :public Item_func
+{
+protected:
+  Item *last_value;
+public:
+  Item_func_last_value(List<Item> &list) :Item_func(list) {}
+  double val_real();
+  longlong val_int();
+  String *val_str(String *);
+  my_decimal *val_decimal(my_decimal *);
+  void fix_length_and_dec();
+  enum Item_result result_type () const { return last_value->result_type(); }
+  const char *func_name() const { return "last_value"; }
+  table_map not_null_tables() const { return 0; }
+  enum_field_types field_type() const { return last_value->field_type(); }
+  bool const_item() const { return 0; }
+  void evaluate_sideeffects();
+};
+
+
 Item *get_system_var(THD *thd, enum_var_type var_type, LEX_STRING name,
                      LEX_STRING component);
 extern bool check_reserved_words(LEX_STRING *name);

sql/lex.h

@@ -302,6 +302,7 @@ static SYMBOL symbols[] = {
   { "KILL",		SYM(KILL_SYM)},
   { "LANGUAGE",         SYM(LANGUAGE_SYM)},
   { "LAST",		SYM(LAST_SYM)},
+  { "LAST_VALUE",	SYM(LAST_VALUE)},
   { "LEADING",		SYM(LEADING)},
   { "LEAVE",            SYM(LEAVE_SYM)},
   { "LEAVES",		SYM(LEAVES)},

sql/sql_yacc.yy

@@ -1064,6 +1064,7 @@ bool my_yyoverflow(short **a, YYSTYPE **b, ulong *yystacksize);
 %token  KILL_SYM
 %token  LANGUAGE_SYM                  /* SQL-2003-R */
 %token  LAST_SYM                      /* SQL-2003-N */
+%token  LAST_VALUE
 %token  LE                            /* OPERATOR */
 %token  LEADING                       /* SQL-2003-R */
 %token  LEAVES
@@ -8890,6 +8891,12 @@ function_call_conflict:
             if ($$ == NULL)
               MYSQL_YYABORT;
           }
+        | LAST_VALUE '(' expr_list ')'
+          {
+            $$= new (YYTHD->mem_root) Item_func_last_value(* $3);
+            if ($$ == NULL)
+              MYSQL_YYABORT;
+          }
         | MICROSECOND_SYM '(' expr ')'
           {
             $$= new (YYTHD->mem_root) Item_func_microsecond($3);
@@ -13088,6 +13095,7 @@ keyword_sp:
         | ISSUER_SYM               {}
         | INSERT_METHOD            {}
         | KEY_BLOCK_SIZE           {}
+        | LAST_VALUE               {}
         | LAST_SYM                 {}
         | LEAVES                   {}
         | LESS_SYM                 {}