MDEV-10342 Providing compatibility for basic SQL built-in functions

Adding the Oracle style DECODE function:

  DECODE(operand, search, result [, search, result ...] [, default_result])

mysql-test/r/keywords.result

@@ -346,3 +346,5 @@ CREATE TABLE raw (raw int);
 DROP TABLE raw;
 CREATE TABLE varchar2 (varchar2 int);
 DROP TABLE varchar2;
+CREATE TABLE decode (decode int);
+DROP TABLE decode;

mysql-test/suite/compat/oracle/r/func_decode.result

+SET sql_mode=ORACLE;
+SELECT DECODE(10);
+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
+SELECT DECODE(10,10);
+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
+SELECT DECODE(10,10,'x10');
+DECODE(10,10,'x10')
+x10
+SELECT DECODE(11,10,'x10');
+DECODE(11,10,'x10')
+NULL
+SELECT DECODE(10,10,'x10','def');
+DECODE(10,10,'x10','def')
+x10
+SELECT DECODE(11,10,'x10','def');
+DECODE(11,10,'x10','def')
+def
+SELECT DECODE(10,10,'x10',11,'x11','def');
+DECODE(10,10,'x10',11,'x11','def')
+x10
+SELECT DECODE(11,10,'x10',11,'x11','def');
+DECODE(11,10,'x10',11,'x11','def')
+x11
+SELECT DECODE(12,10,'x10',11,'x11','def');
+DECODE(12,10,'x10',11,'x11','def')
+def
+EXPLAIN EXTENDED SELECT DECODE(12,10,'x10',11,'x11','def');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+Warnings:
+Note	1003	select (case 12 when 10 then 'x10' when 11 then 'x11' else 'def' end) AS "DECODE(12,10,'x10',11,'x11','def')"
+CREATE TABLE decode (decode int);
+DROP TABLE decode;

mysql-test/suite/compat/oracle/t/func_decode.test

+SET sql_mode=ORACLE;
+
+--error ER_PARSE_ERROR
+SELECT DECODE(10);
+--error ER_PARSE_ERROR
+SELECT DECODE(10,10);
+
+SELECT DECODE(10,10,'x10');
+SELECT DECODE(11,10,'x10');
+
+SELECT DECODE(10,10,'x10','def');
+SELECT DECODE(11,10,'x10','def');
+
+SELECT DECODE(10,10,'x10',11,'x11','def');
+SELECT DECODE(11,10,'x10',11,'x11','def');
+SELECT DECODE(12,10,'x10',11,'x11','def');
+
+EXPLAIN EXTENDED SELECT DECODE(12,10,'x10',11,'x11','def');
+
+CREATE TABLE decode (decode int);
+DROP TABLE decode;

mysql-test/t/keywords.test

@@ -241,3 +241,6 @@ DROP TABLE raw;
 
 CREATE TABLE varchar2 (varchar2 int);
 DROP TABLE varchar2;
+
+CREATE TABLE decode (decode int);
+DROP TABLE decode;

sql/item_create.cc

@@ -882,19 +882,6 @@ class Create_func_dayofyear : public Create_func_arg1
 };
 
 
-class Create_func_decode : public Create_func_arg2
-{
-public:
-  virtual Item *create_2_arg(THD *thd, Item *arg1, Item *arg2);
-
-  static Create_func_decode s_singleton;
-
-protected:
-  Create_func_decode() {}
-  virtual ~Create_func_decode() {}
-};
-
-
 class Create_func_degrees : public Create_func_arg1
 {
 public:
@@ -4067,15 +4054,6 @@ Create_func_dayofyear::create_1_arg(THD *thd, Item *arg1)
 }
 
 
-Create_func_decode Create_func_decode::s_singleton;
-
-Item*
-Create_func_decode::create_2_arg(THD *thd, Item *arg1, Item *arg2)
-{
-  return new (thd->mem_root) Item_func_decode(thd, arg1, arg2);
-}
-
-
 Create_func_degrees Create_func_degrees::s_singleton;
 
 Item*
@@ -6772,7 +6750,6 @@ static Native_func_registry func_array[] =
   { { C_STRING_WITH_LEN("DAYOFMONTH") }, BUILDER(Create_func_dayofmonth)},
   { { C_STRING_WITH_LEN("DAYOFWEEK") }, BUILDER(Create_func_dayofweek)},
   { { C_STRING_WITH_LEN("DAYOFYEAR") }, BUILDER(Create_func_dayofyear)},
-  { { C_STRING_WITH_LEN("DECODE") }, BUILDER(Create_func_decode)},
   { { C_STRING_WITH_LEN("DEGREES") }, BUILDER(Create_func_degrees)},
   { { C_STRING_WITH_LEN("DECODE_HISTOGRAM") }, BUILDER(Create_func_decode_histogram)},
   { { C_STRING_WITH_LEN("DES_DECRYPT") }, BUILDER(Create_func_des_decrypt)},

sql/lex.h

@@ -705,6 +705,7 @@ static SYMBOL sql_functions[] = {
   { "CURTIME",		SYM(CURTIME)},
   { "DATE_ADD",		SYM(DATE_ADD_INTERVAL)},
   { "DATE_SUB",		SYM(DATE_SUB_INTERVAL)},
+  { "DECODE",           SYM(DECODE_SYM)},
   { "DENSE_RANK",       SYM(DENSE_RANK_SYM)},
   { "EXTRACT",		SYM(EXTRACT_SYM)},
   { "FIRST_VALUE",      SYM(FIRST_VALUE_SYM)},

sql/sql_yacc.yy

@@ -1041,6 +1041,7 @@ bool my_yyoverflow(short **a, YYSTYPE **b, ulong *yystacksize);
 %token  DECIMAL_NUM
 %token  DECIMAL_SYM                   /* SQL-2003-R */
 %token  DECLARE_SYM                   /* SQL-2003-R */
+%token  DECODE_SYM                    /* Oracle function, non-reserved */
 %token  DEFAULT                       /* SQL-2003-R */
 %token  DEFINER_SYM
 %token  DELAYED_SYM
@@ -9370,6 +9371,12 @@ function_call_nonkeyword:
             if ($$ == NULL)
               MYSQL_YYABORT;
           }
+        | DECODE_SYM '(' expr ',' expr ')'
+          {
+            $$= new (thd->mem_root) Item_func_decode(thd, $3, $5);
+            if ($$ == NULL)
+              MYSQL_YYABORT;
+          }
         | EXTRACT_SYM '(' interval FROM expr ')'
           {
             $$=new (thd->mem_root) Item_extract(thd, $3, $5);
@@ -14279,6 +14286,7 @@ keyword_sp:
         | DATETIME                 {}
         | DATE_SYM                 {}
         | DAY_SYM                  {}
+        | DECODE_SYM               {}
         | DEFINER_SYM              {}
         | DELAY_KEY_WRITE_SYM      {}
         | DES_KEY_FILE             {}

sql/sql_yacc_ora.yy

@@ -415,6 +415,7 @@ bool my_yyoverflow(short **a, YYSTYPE **b, ulong *yystacksize);
 %token  DECIMAL_NUM
 %token  DECIMAL_SYM                   /* SQL-2003-R */
 %token  DECLARE_SYM                   /* SQL-2003-R */
+%token  DECODE_SYM                    /* Oracle function, non-reserved */
 %token  DEFAULT                       /* SQL-2003-R */
 %token  DEFINER_SYM
 %token  DELAYED_SYM
@@ -1118,6 +1119,7 @@ bool my_yyoverflow(short **a, YYSTYPE **b, ulong *yystacksize);
 %type <item_list>
         expr_list opt_udf_expr_list udf_expr_list when_list
         ident_list ident_list_arg opt_expr_list
+        decode_when_list
 
 %type <var_type>
         option_type opt_var_type opt_var_ident_type
@@ -8850,6 +8852,36 @@ column_default_non_parenthesized_expr:
             if ($$ == NULL)
               MYSQL_YYABORT;
           }
+        | DECODE_SYM '(' expr ',' decode_when_list ')'
+          {
+            if (($5->elements % 2) == 0)
+            {
+              // No default expression
+              $$= new (thd->mem_root) Item_func_case(thd, *$5, $3, NULL);
+            }
+            else
+            {
+              /*
+                There is a default expression at the end of the list $5.
+                Create a new list without the default expression.
+              */
+              List<Item> tmp;
+              List_iterator_fast<Item> it(*$5);
+              for (uint i= 0; i < $5->elements - 1; i++) // copy all but last
+              {
+                Item *item= it++;
+                tmp.push_back(item);
+              }
+              /*
+                Now the new list "tmp" contains only WHEN-THEN pairs,
+                The default expression is pointed by the iterator "it"
+                and will be returned by the next call for it++ below.
+              */
+              $$= new (thd->mem_root) Item_func_case(thd, tmp, $3, it++);
+            }
+            if ($$ == NULL)
+              MYSQL_YYABORT;
+          }
         | DEFAULT '(' simple_ident ')'
           {
             Item_splocal *il= $3->get_item_splocal();
@@ -10246,6 +10278,24 @@ when_list:
           }
         ;
 
+
+decode_when_list:
+          expr ',' expr
+          {
+            $$= new (thd->mem_root) List<Item>;
+            if ($$ == NULL)
+              MYSQL_YYABORT;
+            $$->push_back($1, thd->mem_root);
+            $$->push_back($3, thd->mem_root);
+          }
+        | decode_when_list ',' expr
+          {
+            $$= $1;
+            $$->push_back($3, thd->mem_root);
+          }
+        ;
+
+
 /* Equivalent to <table reference> in the SQL:2003 standard. */
 /* Warning - may return NULL in case of incomplete SELECT */
 table_ref:
@@ -14190,6 +14240,7 @@ keyword_sp:
         | DATETIME                 {}
         | DATE_SYM                 {}
         | DAY_SYM                  {}
+        | DECODE_SYM               {}
         | DEFINER_SYM              {}
         | DELAY_KEY_WRITE_SYM      {}
         | DES_KEY_FILE             {}