diff --git a/1-sys_guid.md b/1-sys_guid.md
new file mode 100644
index 0000000000000000000000000000000000000000..bd233caa85cb630c2b58b43b698b0f0f4b6949fc
--- /dev/null
+++ b/1-sys_guid.md
@@ -0,0 +1,36 @@
+### Oracle兼容函数 sys_guid()
+
+------
+#### 语法
+
+```
+sys_guid（）
+```
+
+#### 定义和用法
+系统根据当前时间和机器码，生成全球唯一的一个32位序列号，32个字符（8，4，4，4，12），前三段（8，4，4）为依据当前时间生成，后两段（4，12）为机器码生成，函数返回数值为长度为32位的字符串，包括0－9和小写a－f
+
+#### Oracle兼容程度说明
+
+MySQL sys_guid产生的序列号意义与Oracle一致，生成唯一的序列号，都是32字符，差异：sys_guid 返回的32位随机数中间包括一些小写的英文字母，
+而oarcle返回中间则为包含大写的英文字母；Oracle不同版本返回值类型存在不同，如返回类型为raw。
+
+#### 示例
+
+```
+mysql> SELECT sys_guid() ;
++----------------------------------+
+| sys_guid()                       |
++----------------------------------+
+| 9f5bed5ea47611ed9b0a0242ac110002 |
++----------------------------------+
+1 row in set (0.00 sec)
+
+mysql> SELECT sys_guid() ;
++----------------------------------+
+| sys_guid()                       |
++----------------------------------+
+| a0832c47a47611ed9b0a0242ac110002 |
++----------------------------------+
+1 row in set (0.00 sec)
+```
\ No newline at end of file
diff --git a/1-sys_guid.patch b/1-sys_guid.patch
new file mode 100644
index 0000000000000000000000000000000000000000..bd3ae5337e2d1553651a6443894650c567f14e3b
--- /dev/null
+++ b/1-sys_guid.patch
@@ -0,0 +1,327 @@
+diff --git a/mysql-test/r/guid.result b/mysql-test/r/guid.result
+new file mode 100644
+index 00000000000..0dce87df7a8
+--- /dev/null
++++ b/mysql-test/r/guid.result
+@@ -0,0 +1,69 @@
++CREATE TABLE t1 (iv INT, cv VARCHAR(10), ncv VARCHAR(40) CHARACTER SET UTF8MB4);
++INSERT INTO t1 VALUES (1, '11111', sys_guid());
++INSERT INTO t1 VALUES (2, '22222', sys_guid());
++INSERT INTO t1 VALUES (3, '33333', sys_guid());
++INSERT INTO t1 VALUES (4, '44444', sys_guid());
++INSERT INTO t1 VALUES (5, '55555', sys_guid());
++INSERT INTO t1 VALUES (6, '66666', sys_guid());
++INSERT INTO t1 VALUES (7, '77777', sys_guid());
++# sys_guid 产生32字符，生成的字符唯一，不能有任何相同
++SELECT LENGTH (ncv) FROM t1;
++LENGTH (ncv)
++32
++32
++32
++32
++32
++32
++32
++SELECT COUNT(DISTINCT ncv) FROM t1;
++COUNT(DISTINCT ncv)
++7
++# sys_guid 产生32字符，如：aaaaaaaabbbbccccddddeeeeeeeeeeee,第五段为依据mac生成，相同库必须一致
++select COUNT(DISTINCT SUBSTR(ncv,20)) from t1;
++COUNT(DISTINCT SUBSTR(ncv,20))
++1
++INSERT INTO t1 VALUES (3, 'greatdb', _UTF8MB4 '万里开源');
++select length(sys_guid())=32;
++length(sys_guid())=32
++1
++select 1 from t1 order by sys_guid();
++1
++1
++1
++1
++1
++1
++1
++1
++1
++select iv from (select iv,sys_guid() from t1 group by iv,sys_guid()) t2;
++iv
++1
++2
++3
++4
++5
++6
++7
++3
++select iv from(select iv,sys_guid(),GROUP_CONCAT(sys_guid() ORDER BY sys_guid() DESC ) from t1 group by iv,sys_guid() order by iv,sys_guid()) t2;
++iv
++1
++2
++3
++3
++4
++5
++6
++7
++select sys_guid() is null,sys_guid() is not null;
++sys_guid() is null	sys_guid() is not null
++0	1
++select count(*) from (select 1 from t1 where sys_guid() is null) t2;
++count(*)
++0
++select count(*) from (select 1 from t1 where sys_guid() is not null) t2;
++count(*)
++8
++DROP TABLE t1;
+diff --git a/mysql-test/t/guid.test b/mysql-test/t/guid.test
+new file mode 100644
+index 00000000000..92faac83ca9
+--- /dev/null
++++ b/mysql-test/t/guid.test
+@@ -0,0 +1,37 @@
++
++# 'ncv NVARCHAR(10)' triggers warning in 8.0.22.
++# Using VARCHAR(40) CHARACTER SET UTF8MB4 to avoid warning.
++CREATE TABLE t1 (iv INT, cv VARCHAR(10), ncv VARCHAR(40) CHARACTER SET UTF8MB4);
++INSERT INTO t1 VALUES (1, '11111', sys_guid());
++INSERT INTO t1 VALUES (2, '22222', sys_guid());
++INSERT INTO t1 VALUES (3, '33333', sys_guid());
++INSERT INTO t1 VALUES (4, '44444', sys_guid());
++INSERT INTO t1 VALUES (5, '55555', sys_guid());
++INSERT INTO t1 VALUES (6, '66666', sys_guid());
++INSERT INTO t1 VALUES (7, '77777', sys_guid());
++
++--echo # sys_guid 产生32字符，生成的字符唯一，不能有任何相同
++SELECT LENGTH (ncv) FROM t1;
++SELECT COUNT(DISTINCT ncv) FROM t1;
++
++--echo # sys_guid 产生32字符，如：aaaaaaaabbbbccccddddeeeeeeeeeeee,第五段为依据mac生成，相同库必须一致
++select COUNT(DISTINCT SUBSTR(ncv,20)) from t1;
++
++
++# n'万里开源' triggers warning in 8.0.22.
++# Specifying UTF8MB4 to avoid warning.
++INSERT INTO t1 VALUES (3, 'greatdb', _UTF8MB4 '万里开源');
++
++#add test case
++select length(sys_guid())=32;
++
++select 1 from t1 order by sys_guid();
++select iv from (select iv,sys_guid() from t1 group by iv,sys_guid()) t2;
++select iv from(select iv,sys_guid(),GROUP_CONCAT(sys_guid() ORDER BY sys_guid() DESC ) from t1 group by iv,sys_guid() order by iv,sys_guid()) t2;
++select sys_guid() is null,sys_guid() is not null;
++select count(*) from (select 1 from t1 where sys_guid() is null) t2;
++select count(*) from (select 1 from t1 where sys_guid() is not null) t2;
++
++DROP TABLE t1;
++
++
+diff --git a/sql/item_strfunc.cc b/sql/item_strfunc.cc
+index c494eabb65e..43fea7ca38a 100644
+--- a/sql/item_strfunc.cc
++++ b/sql/item_strfunc.cc
+@@ -4206,6 +4206,134 @@ String *Item_func_uuid::val_str(String *str) {
+   return mysql_generate_uuid(str);
+ }
+ 
++bool Item_func_sys_guid::resolve_type(THD *) {
++  collation.set(system_charset_info, DERIVATION_COERCIBLE, MY_REPERTOIRE_ASCII);
++  set_data_type_string(uint32(UUID_LENGTH - 4));
++  return false;
++}
++
++bool Item_func_sys_guid::itemize(Parse_context *pc, Item **res) {
++  if (skip_itemize(res)) return false;
++  if (super::itemize(pc, res)) return true;
++  pc->thd->lex->set_stmt_unsafe(LEX::BINLOG_STMT_UNSAFE_SYSTEM_FUNCTION);
++  pc->thd->lex->safe_to_cache_query = false;
++  return false;
++}
++
++String *mysql_generate_sys_guid(String *str) {
++  char *s;
++  THD *thd = current_thd;
++
++  mysql_mutex_lock(&LOCK_uuid_generator);
++  if (!uuid_time) /* first UUID() call. initializing data */
++  {
++    ulong tmp = sql_rnd_with_mutex();
++    uchar mac[6];
++    int i;
++    if (my_gethwaddr(mac)) {
++      /* purecov: begin inspected */
++      /*
++        generating random "hardware addr"
++        and because specs explicitly specify that it should NOT correlate
++        with a clock_seq value (initialized random below), we use a separate
++        randominit() here
++      */
++      randominit(&uuid_rand, tmp + (ulong)thd,
++                 tmp + (ulong)atomic_global_query_id);
++      for (i = 0; i < (int)sizeof(mac); i++)
++        mac[i] = (uchar)(my_rnd(&uuid_rand) * 255);
++      /* purecov: end */
++    }
++    s = clock_seq_and_node_str + sizeof(clock_seq_and_node_str) - 1;
++    for (i = sizeof(mac) - 1; i >= 0; i--) {
++      *--s = _dig_vec_lower[mac[i] & 15];
++      *--s = _dig_vec_lower[mac[i] >> 4];
++    }
++    randominit(&uuid_rand, tmp + (ulong)server_start_time,
++               tmp + (ulong)thd->status_var.bytes_sent);
++    set_clock_seq_str();
++  }
++
++  ulonglong tv = my_getsystime() + UUID_TIME_OFFSET + nanoseq;
++
++  if (likely(tv > uuid_time)) {
++    /*
++      Current time is ahead of last timestamp, as it should be.
++      If we "borrowed time", give it back, just as long as we
++      stay ahead of the previous timestamp.
++    */
++    if (nanoseq) {
++      assert((tv > uuid_time) && (nanoseq > 0));
++      /*
++        -1 so we won't make tv= uuid_time for nanoseq >= (tv - uuid_time)
++      */
++      ulong delta = min<ulong>(nanoseq, (ulong)(tv - uuid_time - 1));
++      tv -= delta;
++      nanoseq -= delta;
++    }
++  } else {
++    if (unlikely(tv == uuid_time)) {
++      /*
++        For low-res system clocks. If several requests for UUIDs
++        end up on the same tick, we add a nano-second to make them
++        different.
++        ( current_timestamp + nanoseq * calls_in_this_period )
++        may end up > next_timestamp; this is OK. Nonetheless, we'll
++        try to unwind nanoseq when we get a chance to.
++        If nanoseq overflows, we'll start over with a new numberspace
++        (so the if() below is needed so we can avoid the ++tv and thus
++        match the follow-up if() if nanoseq overflows!).
++      */
++      if (likely(++nanoseq)) ++tv;
++    }
++
++    if (unlikely(tv <= uuid_time)) {
++      /*
++        If the admin changes the system clock (or due to Daylight
++        Saving Time), the system clock may be turned *back* so we
++        go through a period once more for which we already gave out
++        UUIDs.  To avoid duplicate UUIDs despite potentially identical
++        times, we make a new random component.
++        We also come here if the nanoseq "borrowing" overflows.
++        In either case, we throw away any nanoseq borrowing since it's
++        irrelevant in the new numberspace.
++      */
++      set_clock_seq_str();
++      tv = my_getsystime() + UUID_TIME_OFFSET;
++      nanoseq = 0;
++      DBUG_PRINT("uuid", ("making new numberspace"));
++    }
++  }
++
++  uuid_time = tv;
++  mysql_mutex_unlock(&LOCK_uuid_generator);
++
++  uint32 time_low = (uint32)(tv & 0xFFFFFFFF);
++  uint16 time_mid = (uint16)((tv >> 32) & 0xFFFF);
++  uint16 time_hi_and_version = (uint16)((tv >> 48) | UUID_VERSION);
++
++  str->mem_realloc(UUID_LENGTH + 1 - 4);
++  str->length(UUID_LENGTH - 4);
++  str->set_charset(system_charset_info);
++  s = str->ptr();
++  // s[8] = s[13] = '-';
++  tohex(s, time_low, 8);
++  tohex(s + 8, time_mid, 4);
++  tohex(s + 12, time_hi_and_version, 4);
++  int j, k = 16;
++  for (j = 0; clock_seq_and_node_str[j] != '\0'; j++)
++    if (clock_seq_and_node_str[j] != '-') s[k++] = clock_seq_and_node_str[j];
++
++  DBUG_EXECUTE_IF("force_fake_guid",
++                  my_stpcpy(s, "a2d00942b69c11e4a6960020ff6fcbe6"););
++  return str;
++}
++
++String *Item_func_sys_guid::val_str(String *str) {
++  assert(fixed == 1);
++  return mysql_generate_sys_guid(str);
++}
++
+ bool Item_func_gtid_subtract::resolve_type(THD *thd) {
+   if (param_type_is_default(thd, 0, -1)) return true;
+   set_nullable(args[0]->is_nullable() || args[1]->is_nullable());
+diff --git a/sql/item_strfunc.h b/sql/item_strfunc.h
+index e4a8506a7cb..4424a6f136c 100644
+--- a/sql/item_strfunc.h
++++ b/sql/item_strfunc.h
+@@ -1303,6 +1303,30 @@ class Item_func_uuid final : public Item_str_func {
+   Item *pq_clone(THD *thd, Query_block *select) override;
+ };
+ 
++class Item_func_sys_guid final : public Item_str_func {
++  typedef Item_str_func super;
++
++ public:
++  Item_func_sys_guid() : Item_str_func() {}
++  explicit Item_func_sys_guid(const POS &pos) : Item_str_func(pos) {}
++
++  bool itemize(Parse_context *pc, Item **res) override;
++  table_map get_initial_pseudo_tables() const override {
++    return RAND_TABLE_BIT;
++  }
++  bool resolve_type(THD *) override;
++  const char *func_name() const override { return "sys_guid"; }
++  String *val_str(String *) override;
++  bool check_function_as_value_generator(uchar *checker_args) override {
++    Check_function_as_value_generator_parameters *func_arg =
++        pointer_cast<Check_function_as_value_generator_parameters *>(
++            checker_args);
++    func_arg->banned_function_name = func_name();
++    return ((func_arg->source == VGS_GENERATED_COLUMN) ||
++            (func_arg->source == VGS_CHECK_CONSTRAINT));
++  }
++};
++
+ class Item_func_gtid_subtract final : public Item_str_ascii_func {
+   String buf1, buf2;
+ 
+diff --git a/sql/lex.h b/sql/lex.h
+index e14e76f6963..a7251ee2968 100644
+--- a/sql/lex.h
++++ b/sql/lex.h
+@@ -863,6 +863,7 @@ static const SYMBOL symbols[] = {
+     {SYM_FN("ST_COLLECT", ST_COLLECT_SYM)},
+     {SYM_FN("SUBDATE", SUBDATE_SYM)},
+     {SYM_FN("SUBSTR", SUBSTRING)},
++    {SYM_FN("SYS_GUID", SYS_GUID_SYM)},
+     {SYM_FN("SUBSTRING", SUBSTRING)},
+     {SYM_FN("SUM", SUM_SYM)},
+     {SYM_FN("SYSDATE", SYSDATE)},
+diff --git a/sql/sql_yacc.yy b/sql/sql_yacc.yy
+index 2b6bc52bafc..35aaab16c2b 100644
+--- a/sql/sql_yacc.yy
++++ b/sql/sql_yacc.yy
+@@ -1376,6 +1376,7 @@ void warn_about_deprecated_binary(THD *thd)
+ */
+ %token<lexer.keyword> EFFECTIVE_SYM 1350
+ %token  SEQUENCE_TABLE_SYM 1351
++%token SYS_GUID_SYM 1352
+ 
+ /*
+   Precedence rules used to resolve the ambiguity when using keywords as idents
+@@ -10892,6 +10893,10 @@ function_call_nonkeyword:
+             $$= NEW_PTN PTI_function_call_nonkeyword_sysdate(@$,
+               static_cast<uint8>($2));
+           }
++        | SYS_GUID_SYM '(' ')'
++          {
++            $$= NEW_PTN Item_func_sys_guid(@$);
++          }
+         | TIMESTAMP_ADD '(' interval_time_stamp ',' expr ',' expr ')'
+           {
+             $$= NEW_PTN Item_date_add_interval(@$, $7, $5, $3, 0);
\ No newline at end of file
diff --git a/2-decode.md b/2-decode.md
new file mode 100644
index 0000000000000000000000000000000000000000..a7290245bd866ea7221557362c0bbaf5866b7fe3
--- /dev/null
+++ b/2-decode.md
@@ -0,0 +1,37 @@
+### Oracle兼容函数 decode()
+
+------
+
+#### 语法
+
+```sql
+decode(
+    expr,                   /* 字段或表达式 */
+    search,                 /* 可能值 */
+    result                  /* 返回值 */
+    [, search, result ]...  /* 可选可能值/返回值对[允许多个] */
+    [, default ]            /* 可选无匹配返回值 */
+)
+```
+
+#### 定义和用法
+
+比较`expr`和`search`的结果，如果一致则返回对应的`result`，如果所有条件都不匹配则返回`default`，如果`default`不存在，则返回NULL。
+
+对于`expr=search=NULL`，的情况与Oracle行为一致，会返回第一个`search`为NULL的`result`。
+
+注意：
+
+- 可能值与返回值的评估使用`短路评估`，即：只要存在`expr`=`search`则后续`search`不会被评估
+
+
+#### 示例
+
+```sql
+> SELECT decode(1, 1, 'one', 2, 'two', 'other');
++----------------------------------------+
+| decode(1, 1, 'one', 2, 'two', 'other') |
++----------------------------------------+
+| one                                    |
++----------------------------------------+
+```
\ No newline at end of file
diff --git a/2-decode.patch b/2-decode.patch
new file mode 100644
index 0000000000000000000000000000000000000000..c947fb192386f86a11b4376f163c254841d23ab1
--- /dev/null
+++ b/2-decode.patch
@@ -0,0 +1,565 @@
+diff --git a/mysql-test/r/decode.result b/mysql-test/r/decode.result
+new file mode 100644
+index 00000000000..84e8b991498
+--- /dev/null
++++ b/mysql-test/r/decode.result
+@@ -0,0 +1,226 @@
++drop table if exists t1, t2;
++SET sql_mode = 'NO_ENGINE_SUBSTITUTION';
++select DECODE("b", "a", 1, "b", 2);
++DECODE("b", "a", 1, "b", 2)
++2
++select DECODE("c", "a", 1, "b", 2);
++DECODE("c", "a", 1, "b", 2)
++NULL
++select DECODE("c", "a", 1, "b", 2, 3);
++DECODE("c", "a", 1, "b", 2, 3)
++3
++select DECODE(BINARY "b", "a", 1, "B", 2, "b", "ok");
++DECODE(BINARY "b", "a", 1, "B", 2, "b", "ok")
++ok
++select DECODE("b", "a", 1, "B", 2, "b", "ok");
++DECODE("b", "a", 1, "B", 2, "b", "ok")
++2
++select DECODE(concat("a","b"), concat("ab",""), "a", "b", "b");
++DECODE(concat("a","b"), concat("ab",""), "a", "b", "b")
++a
++select DECODE(1=0, false, "true", "false");
++DECODE(1=0, false, "true", "false")
++true
++select DECODE(1, 1, "one", 2, "two", "more");
++DECODE(1, 1, "one", 2, "two", "more")
++one
++explain select DECODE(1, 1, "one", 2, "two", "more");
++id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
++1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
++Warnings:
++Note	1003	/* select#1 */ select decode(1,1,'one',2,'two','more') AS `DECODE(1, 1, "one", 2, "two", "more")`
++select DECODE(2.0, 1, "one", 2.0, "two", "more");
++DECODE(2.0, 1, "one", 2.0, "two", "more")
++two
++select DECODE(1, 1, true, 1, false) from dual;
++DECODE(1, 1, true, 1, false)
++1
++select DECODE("two", "one", "1", "two", "2") | 0;
++DECODE("two", "one", "1", "two", "2") | 0
++2
++select DECODE("two","one", 1.00, "two", 2.00) +0.0;
++DECODE("two","one", 1.00, "two", 2.00) +0.0
++2.00
++select DECODE(1/0, "a", "true", "false");
++DECODE(1/0, "a", "true", "false")
++false
++select DECODE(1/0, "a", "true");
++DECODE(1/0, "a", "true")
++NULL
++select DECODE(1/0, "a", "true") | 0;
++DECODE(1/0, "a", "true") | 0
++NULL
++select DECODE(1/0, "a", "true") + 0.0;
++DECODE(1/0, "a", "true") + 0.0
++NULL
++select DECODE(1>0, true, "TRUE", "FALSE");
++DECODE(1>0, true, "TRUE", "FALSE")
++TRUE
++select DECODE(1<0, false, "TRUE", "FALSE");
++DECODE(1<0, false, "TRUE", "FALSE")
++TRUE
++create table t1 (a int);
++insert into t1 values(1),(2),(3),(4);
++select decode(a, 1, 2, 2, 3, 0) as fcase, count(*) from t1 group by fcase;
++fcase	count(*)
++2	1
++3	1
++0	2
++analyze table t1;
++Table	Op	Msg_type	Msg_text
++test.t1	analyze	status	OK
++explain select decode(a, 1, 2, 2, 3, 0) as fcase, count(*) from t1 group by fcase;
++id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
++1	SIMPLE	t1	NULL	ALL	NULL	NULL	NULL	NULL	4	100.00	Using temporary
++Warnings:
++Note	1003	/* select#1 */ select decode(`test`.`t1`.`a`,1,2,2,3,0) AS `fcase`,count(0) AS `count(*)` from `test`.`t1` group by `fcase`
++select decode(a, 1, "one", 2, "two", "nothing") as fcase, count(*) from t1 group by fcase;
++fcase	count(*)
++one	1
++two	1
++nothing	2
++drop table t1;
++create table t1 (`row` int not null, col int not null, val varchar(255) not null);
++insert into t1 values (1,1,'orange'),(1,2,'large'),(2,1,'yellow'),(2,2,'medium'),(3,1,'green'),(3,2,'small');
++select max(decode(col, 1, val, null)) as color from t1 group by `row`;
++color
++orange
++yellow
++green
++drop table t1;
++SET NAMES latin1;
++CREATE TABLE t1 SELECT 
++DECODE(1, true, _latin1'a' COLLATE latin1_danish_ci, _latin1'a') AS c1,
++DECODE(1, true, _latin1'a', _latin1'a' COLLATE latin1_danish_ci) AS c2,
++DECODE(1, true, 'a', 1) AS c3,
++DECODE(1, true, 1, 'a') AS c4,
++DECODE(1, true, 'a', 1.0) AS c5,
++DECODE(1, true, 1.0, 'a') AS c6,
++DECODE(1, true, 1, 1.0) AS c7,
++DECODE(1, true, 1.0, 1) AS c8,
++DECODE(1, true, 1.0) AS c9,
++DECODE(1, true, 0.1e1, 0.1) AS c10,
++DECODE(1, true, 0.1e1, 1) AS c11,
++DECODE(1, true, 0.1e1, '1') AS c12
++;
++SHOW CREATE TABLE t1;
++Table	Create Table
++t1	CREATE TABLE `t1` (
++  `c1` varchar(1) CHARACTER SET latin1 COLLATE latin1_danish_ci NOT NULL DEFAULT '',
++  `c2` varchar(1) CHARACTER SET latin1 COLLATE latin1_danish_ci NOT NULL DEFAULT '',
++  `c3` varchar(1) CHARACTER SET latin1 NOT NULL DEFAULT '',
++  `c4` varchar(1) CHARACTER SET latin1 NOT NULL DEFAULT '',
++  `c5` varchar(4) CHARACTER SET latin1 NOT NULL DEFAULT '',
++  `c6` varchar(4) CHARACTER SET latin1 NOT NULL DEFAULT '',
++  `c7` decimal(2,1) NOT NULL DEFAULT '0.0',
++  `c8` decimal(2,1) NOT NULL DEFAULT '0.0',
++  `c9` decimal(2,1) DEFAULT NULL,
++  `c10` double NOT NULL DEFAULT '0',
++  `c11` double NOT NULL DEFAULT '0',
++  `c12` varchar(22) CHARACTER SET latin1 NOT NULL DEFAULT ''
++) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
++DROP TABLE t1;
++SELECT DECODE(1, true, _latin1'a' COLLATE latin1_danish_ci, _latin1'a' COLLATE latin1_swedish_ci);
++ERROR HY000: Illegal mix of collations (latin1_danish_ci,EXPLICIT) and (latin1_swedish_ci,EXPLICIT) for operation 'case'
++SELECT DECODE(_latin1'a' COLLATE latin1_general_ci, 
++_latin1'a' COLLATE latin1_danish_ci, 1,
++_latin1'a' COLLATE latin1_swedish_ci, 2
++);
++ERROR HY000: Illegal mix of collations (latin1_general_ci,EXPLICIT), (latin1_danish_ci,EXPLICIT), (latin1_swedish_ci,EXPLICIT) for operation 'case'
++SELECT 
++DECODE(_latin1'a' COLLATE latin1_general_ci, _latin1'A', '1', 2),
++DECODE(_latin1'a' COLLATE latin1_bin, _latin1'A', '1', 2),
++DECODE(_latin1'a', _latin1'A' COLLATE latin1_swedish_ci, '1', 2),
++DECODE(_latin1'a', _latin1'A' COLLATE latin1_bin, '1', 2);
++DECODE(_latin1'a' COLLATE latin1_general_ci, _latin1'A', '1', 2)	DECODE(_latin1'a' COLLATE latin1_bin, _latin1'A', '1', 2)	DECODE(_latin1'a', _latin1'A' COLLATE latin1_swedish_ci, '1', 2)	DECODE(_latin1'a', _latin1'A' COLLATE latin1_bin, '1', 2)
++1	2	1	2
++SELECT 'decode+union+test'
++UNION 
++SELECT DECODE(LOWER('1'), LOWER('2'), 'BUG', 'nobug');
++decode+union+test
++decode+union+test
++nobug
++SELECT DECODE(LOWER('1'), LOWER('2'), 'BUG', 'nobug');
++DECODE(LOWER('1'), LOWER('2'), 'BUG', 'nobug')
++nobug
++create table t1(a float, b int default 3);
++insert into t1 (a) values (2), (11), (8);
++select min(a), min(decode(1=1, true, a, NULL)),
++min(decode(1!=1, true, NULL, a)) 
++from t1 where b=3 group by b;
++min(a)	min(decode(1=1, true, a, NULL))	min(decode(1!=1, true, NULL, a))
++2	2	2
++drop table t1;
++create table t1 (a int, b bigint unsigned);
++create table t2 (c int);
++insert into t1 (a, b) values (1,4572794622775114594), (2,18196094287899841997),
++(3,11120436154190595086);
++insert into t2 (c) values (1), (2), (3);
++select t1.a, decode(t1.a, 0, 0, t1.b) d from t1 
++join t2 on t1.a=t2.c order by d;
++a	d
++1	4572794622775114594
++3	11120436154190595086
++2	18196094287899841997
++select t1.a, decode(t1.a, 0, 0, t1.b) d from t1 
++join t2 on t1.a=t2.c where b=11120436154190595086 order by d;
++a	d
++3	11120436154190595086
++drop table t1, t2;
++CREATE TABLE t1(a YEAR);
++SELECT 1 FROM t1 WHERE a=1 AND DECODE(1, a, 1, 1);
++1
++DROP TABLE t1;
++SET sql_mode = default;
++CREATE TABLE source(bt INTEGER, bf INTEGER, i8u BIGINT UNSIGNED, i8s BIGINT);
++INSERT INTO source VALUES
++(1,0,0,-9223372036854775808), (1,0,18446744073709551615,9223372036854775807);
++CREATE TABLE target
++SELECT DECODE(bt, i8u, i8s) as u,
++DECODE(bf, i8u, i8s) as s
++FROM source;
++SHOW CREATE TABLE target;
++Table	Create Table
++target	CREATE TABLE `target` (
++  `u` bigint DEFAULT NULL,
++  `s` bigint DEFAULT NULL
++) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
++SELECT DECODE(bt, true, i8u, i8s) AS u,
++DECODE(bf, true, i8u, i8s) AS s
++FROM source;
++u	s
++0	-9223372036854775808
++18446744073709551615	9223372036854775807
++SELECT * FROM target;
++u	s
++NULL	-9223372036854775808
++NULL	NULL
++DROP TABLE target;
++#
++# Test for a memory leak in WL#6570
++#
++CREATE TABLE t1 (a VARCHAR(110));
++INSERT INTO t1 VALUES (REPEAT("a",100));
++SELECT (t1.a,t1.a) IN (('a','c'),('a','b')) END FROM t1;
++END
++0
++SELECT DECODE(t1.a, 'a', 'c', 'd') FROM t1;
++DECODE(t1.a, 'a', 'c', 'd')
++d
++DROP TABLE t1;
++DROP TABLE source;
++#
++# test null in expr.
++#
++SELECT decode(null, 1, 'one', null, 'is_null', 'others');
++decode(null, 1, 'one', null, 'is_null', 'others')
++is_null
++SELECT decode(null, null, 'is_null', 2, 'two', 'others');
++decode(null, null, 'is_null', 2, 'two', 'others')
++is_null
++SELECT decode(null, 2, 'two', 'others');
++decode(null, 2, 'two', 'others')
++others
++SELECT decode(null, 2, 'two');
++decode(null, 2, 'two')
++NULL
+diff --git a/mysql-test/t/decode.test b/mysql-test/t/decode.test
+new file mode 100644
+index 00000000000..d114a0cdd38
+--- /dev/null
++++ b/mysql-test/t/decode.test
+@@ -0,0 +1,170 @@
++# Testing of DECODE
++# 
++# note: almost all test cases are migrated from CASE, even bug num.
++
++--disable_warnings
++drop table if exists t1, t2;
++--enable_warnings
++
++SET sql_mode = 'NO_ENGINE_SUBSTITUTION';
++
++
++select DECODE("b", "a", 1, "b", 2);
++select DECODE("c", "a", 1, "b", 2);
++select DECODE("c", "a", 1, "b", 2, 3);
++select DECODE(BINARY "b", "a", 1, "B", 2, "b", "ok");
++select DECODE("b", "a", 1, "B", 2, "b", "ok");
++select DECODE(concat("a","b"), concat("ab",""), "a", "b", "b");
++select DECODE(1=0, false, "true", "false");
++select DECODE(1, 1, "one", 2, "two", "more");
++explain select DECODE(1, 1, "one", 2, "two", "more");
++select DECODE(2.0, 1, "one", 2.0, "two", "more");
++select DECODE(1, 1, true, 1, false) from dual;
++select DECODE("two", "one", "1", "two", "2") | 0; 
++select DECODE("two","one", 1.00, "two", 2.00) +0.0;
++select DECODE(1/0, "a", "true", "false");
++select DECODE(1/0, "a", "true");
++select DECODE(1/0, "a", "true") | 0;
++select DECODE(1/0, "a", "true") + 0.0;
++select DECODE(1>0, true, "TRUE", "FALSE");
++select DECODE(1<0, false, "TRUE", "FALSE");
++
++#
++# Test GROUP BY on DECODE
++#
++
++create table t1 (a int);
++insert into t1 values(1),(2),(3),(4);
++select decode(a, 1, 2, 2, 3, 0) as fcase, count(*) from t1 group by fcase;
++analyze table t1;
++explain select decode(a, 1, 2, 2, 3, 0) as fcase, count(*) from t1 group by fcase;
++select decode(a, 1, "one", 2, "two", "nothing") as fcase, count(*) from t1 group by fcase;
++drop table t1;
++
++#
++# Test MAX(DECODE(...)) that can return null
++#
++
++create table t1 (`row` int not null, col int not null, val varchar(255) not null);
++insert into t1 values (1,1,'orange'),(1,2,'large'),(2,1,'yellow'),(2,2,'medium'),(3,1,'green'),(3,2,'small');
++select max(decode(col, 1, val, null)) as color from t1 group by `row`;
++drop table t1;
++
++SET NAMES latin1;
++
++#
++# DECODE and argument types/collations aggregation into result 
++#
++CREATE TABLE t1 SELECT 
++ DECODE(1, true, _latin1'a' COLLATE latin1_danish_ci, _latin1'a') AS c1,
++ DECODE(1, true, _latin1'a', _latin1'a' COLLATE latin1_danish_ci) AS c2,
++ DECODE(1, true, 'a', 1) AS c3,
++ DECODE(1, true, 1, 'a') AS c4,
++ DECODE(1, true, 'a', 1.0) AS c5,
++ DECODE(1, true, 1.0, 'a') AS c6,
++ DECODE(1, true, 1, 1.0) AS c7,
++ DECODE(1, true, 1.0, 1) AS c8,
++ DECODE(1, true, 1.0) AS c9,
++ DECODE(1, true, 0.1e1, 0.1) AS c10,
++ DECODE(1, true, 0.1e1, 1) AS c11,
++ DECODE(1, true, 0.1e1, '1') AS c12
++;
++SHOW CREATE TABLE t1;
++DROP TABLE t1;
++
++--error 1267
++SELECT DECODE(1, true, _latin1'a' COLLATE latin1_danish_ci, _latin1'a' COLLATE latin1_swedish_ci);
++
++--error 1270
++SELECT DECODE(_latin1'a' COLLATE latin1_general_ci, 
++_latin1'a' COLLATE latin1_danish_ci, 1,
++_latin1'a' COLLATE latin1_swedish_ci, 2
++);
++
++SELECT 
++DECODE(_latin1'a' COLLATE latin1_general_ci, _latin1'A', '1', 2),
++DECODE(_latin1'a' COLLATE latin1_bin, _latin1'A', '1', 2),
++DECODE(_latin1'a', _latin1'A' COLLATE latin1_swedish_ci, '1', 2),
++DECODE(_latin1'a', _latin1'A' COLLATE latin1_bin, '1', 2);
++
++# Test for BUG#10151
++SELECT 'decode+union+test'
++UNION 
++SELECT DECODE(LOWER('1'), LOWER('2'), 'BUG', 'nobug');
++
++SELECT DECODE(LOWER('1'), LOWER('2'), 'BUG', 'nobug');
++
++
++#
++#test MIN(DECODE(...))
++#
++
++create table t1(a float, b int default 3);
++insert into t1 (a) values (2), (11), (8);
++select min(a), min(decode(1=1, true, a, NULL)),
++  min(decode(1!=1, true, NULL, a)) 
++from t1 where b=3 group by b;
++drop table t1;
++
++
++#
++# #30782: Truncated UNSIGNED BIGINT columns 
++#
++create table t1 (a int, b bigint unsigned);
++create table t2 (c int);
++insert into t1 (a, b) values (1,4572794622775114594), (2,18196094287899841997),
++  (3,11120436154190595086);
++insert into t2 (c) values (1), (2), (3);
++select t1.a, decode(t1.a, 0, 0, t1.b) d from t1 
++  join t2 on t1.a=t2.c order by d;
++select t1.a, decode(t1.a, 0, 0, t1.b) d from t1 
++  join t2 on t1.a=t2.c where b=11120436154190595086 order by d;
++drop table t1, t2;
++
++#
++# Bug #11764313 57135: CRASH IN ITEM_FUNC_CASE::FIND_ITEM WITH CASE WHEN
++# ELSE CLAUSE
++#
++CREATE TABLE t1(a YEAR);
++SELECT 1 FROM t1 WHERE a=1 AND DECODE(1, a, 1, 1);
++DROP TABLE t1;
++
++SET sql_mode = default;
++CREATE TABLE source(bt INTEGER, bf INTEGER, i8u BIGINT UNSIGNED, i8s BIGINT);
++INSERT INTO source VALUES
++(1,0,0,-9223372036854775808), (1,0,18446744073709551615,9223372036854775807);
++
++CREATE TABLE target
++SELECT DECODE(bt, i8u, i8s) as u,
++       DECODE(bf, i8u, i8s) as s
++FROM source;
++
++SHOW CREATE TABLE target;
++
++SELECT DECODE(bt, true, i8u, i8s) AS u,
++       DECODE(bf, true, i8u, i8s) AS s
++FROM source;
++
++SELECT * FROM target;
++
++DROP TABLE target;
++
++--echo #
++--echo # Test for a memory leak in WL#6570
++--echo #
++
++CREATE TABLE t1 (a VARCHAR(110));
++INSERT INTO t1 VALUES (REPEAT("a",100));
++SELECT (t1.a,t1.a) IN (('a','c'),('a','b')) END FROM t1;
++SELECT DECODE(t1.a, 'a', 'c', 'd') FROM t1;
++DROP TABLE t1;
++DROP TABLE source;
++
++
++--echo #
++--echo # test null in expr.
++--echo #
++SELECT decode(null, 1, 'one', null, 'is_null', 'others');
++SELECT decode(null, null, 'is_null', 2, 'two', 'others');
++SELECT decode(null, 2, 'two', 'others');
++SELECT decode(null, 2, 'two');
+diff --git a/sql/item_cmpfunc.cc b/sql/item_cmpfunc.cc
+index fc8284df4dc..c8c88fb1aed 100644
+--- a/sql/item_cmpfunc.cc
++++ b/sql/item_cmpfunc.cc
+@@ -3666,7 +3666,12 @@ Item *Item_func_case::find_item(String *) {
+     }
+   } else {
+     /* Compare every WHEN argument with it and return the first match */
++    bool ora_check_null = (orafun == 1) && args[first_expr_num]->is_null();
+     for (uint i = 0; i < ncases; i += 2) {
++      if (ora_check_null) {
++        if (args[i]->is_null()) return args[i + 1];
++        continue;
++      }
+       if (args[i]->real_item()->type() == NULL_ITEM) continue;
+       cmp_type = item_cmp_type(left_result_type, args[i]->result_type());
+       assert(cmp_type != ROW_RESULT);
+@@ -4044,6 +4049,23 @@ uint Item_func_case::decimal_precision() const {
+ 
+ void Item_func_case::print(const THD *thd, String *str,
+                            enum_query_type query_type) const {
++  if (orafun == 1) {
++    assert(first_expr_num != -1);
++    str->append(STRING_WITH_LEN("decode("));
++    args[first_expr_num]->print(thd, str, query_type);
++    for (uint i = 0; i < ncases; i += 2) {
++      str->append(',');
++      args[i]->print(thd, str, query_type);
++      str->append(',');
++      args[i + 1]->print(thd, str, query_type);
++    }
++    if (else_expr_num != -1) {
++      str->append(',');
++      args[else_expr_num]->print(thd, str, query_type);
++    }
++    str->append(STRING_WITH_LEN(")"));
++    return;
++  }
+   str->append(STRING_WITH_LEN("(case "));
+   if (first_expr_num != -1) {
+     args[first_expr_num]->print(thd, str, query_type);
+diff --git a/sql/item_cmpfunc.h b/sql/item_cmpfunc.h
+index 13ec2f38257..555423c3397 100644
+--- a/sql/item_cmpfunc.h
++++ b/sql/item_cmpfunc.h
+@@ -1970,9 +1970,12 @@ class Item_func_case final : public Item_func {
+   cmp_item *cmp_items[5]; /* For all result types */
+   cmp_item *case_item;
+ 
++  // from oracmp function. 1:decode
++  uint orafun{0};
++
+  public:
+   Item_func_case(const POS &pos, mem_root_deque<Item *> *list,
+-                 Item *first_expr_arg, Item *else_expr_arg)
++                 Item *first_expr_arg, Item *else_expr_arg, int ora_arg = 0)
+       : super(pos),
+         first_expr_num(-1),
+         else_expr_num(-1),
+@@ -1991,6 +1994,7 @@ class Item_func_case final : public Item_func {
+     }
+     set_arguments(list, true);
+     memset(&cmp_items, 0, sizeof(cmp_items));
++    orafun = ora_arg;
+   }
+   ~Item_func_case() override;
+   int get_first_expr_num() const { return first_expr_num; }
+diff --git a/sql/lex.h b/sql/lex.h
+index a7251ee2968..67c5967f550 100644
+--- a/sql/lex.h
++++ b/sql/lex.h
+@@ -846,6 +846,7 @@ static const SYMBOL symbols[] = {
+     {SYM_FN("CURTIME", CURTIME)},
+     {SYM_FN("DATE_ADD", DATE_ADD_INTERVAL)},
+     {SYM_FN("DATE_SUB", DATE_SUB_INTERVAL)},
++    {SYM_FN("DECODE", DECODE_SYM)},
+     {SYM_FN("EXTRACT", EXTRACT_SYM)},
+     {SYM_FN("GROUP_CONCAT", GROUP_CONCAT_SYM)},
+     {SYM_FN("JSON_OBJECTAGG", JSON_OBJECTAGG)},
+diff --git a/sql/sql_yacc.yy b/sql/sql_yacc.yy
+index 35aaab16c2b..dfb7a854cbf 100644
+--- a/sql/sql_yacc.yy
++++ b/sql/sql_yacc.yy
+@@ -1371,6 +1371,8 @@ void warn_about_deprecated_binary(THD *thd)
+ %token<lexer.keyword> USER_STATS_SYM 1307
+ %token<lexer.keyword> ENCRYPTION_KEY_ID_SYM 1308
+ 
++%token<lexer.keyword> DECODE_SYM 1360
++
+ /*
+    Tokens from Percona Server 8.0
+ */
+@@ -1524,7 +1526,7 @@ void warn_about_deprecated_binary(THD *thd)
+ 
+ %type <item>
+         literal insert_ident temporal_literal
+-        simple_ident expr opt_expr opt_else
++        simple_ident expr opt_expr opt_else opt_decode_expr
+         set_function_specification sum_expr
+         in_sum_expr grouping_operation
+         window_func_call opt_ll_default
+@@ -1569,6 +1571,7 @@ void warn_about_deprecated_binary(THD *thd)
+         opt_filter_table_list filter_table_list
+         opt_filter_string_list filter_string_list
+         opt_filter_db_pair_list filter_db_pair_list
++        decode_list
+ 
+ %type <item_list2>
+         expr_list udf_expr_list opt_udf_expr_list opt_expr_list select_item_list
+@@ -10637,6 +10640,10 @@ simple_expr:
+           {
+             $$= NEW_PTN Item_func_case(@$, $3, $2, $4 );
+           }
++        | DECODE_SYM '(' expr decode_list opt_decode_expr ')'
++          {
++            $$= NEW_PTN Item_func_case(@$, $4, $3, $5, 1);
++          }
+         | CONVERT_SYM '(' expr ',' cast_type ')'
+           {
+             $$= create_func_cast(YYTHD, @3, $3, $5, false);
+@@ -11894,6 +11901,11 @@ opt_else:
+         | ELSE expr    { $$= $2; }
+         ;
+ 
++opt_decode_expr:
++          /* empty */  { $$= NULL; }
++        |',' expr      { $$= $2; }
++        ;
++
+ when_list:
+           WHEN_SYM expr THEN_SYM expr
+           {
+@@ -11930,6 +11942,25 @@ esc_table_reference:
+           table_factor { $$= $1; }
+         | joined_table { $$= $1; }
+         ;
++
++decode_list:
++          ',' expr ',' expr
++          {
++            $$ = new (YYMEM_ROOT) mem_root_deque<Item *>(YYMEM_ROOT);
++
++            if($$ == NULL)
++                MYSQL_YYABORT;
++            $$->push_back($2);
++            $$->push_back($4);
++          }
++        | decode_list ',' expr ',' expr
++          {
++            $1->push_back($3);
++            $1->push_back($5);
++            $$=$1;
++          }
++        ;
++
+ /*
+   Join operations are normally left-associative, as in
\ No newline at end of file