RAWTOHEX function implementation

CN/modules/ROOT/nav.adoc

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 *** 内置函数
 **** xref:master/oracle_builtin_functions/sys_context.adoc[sys_context]
 **** xref:master/oracle_builtin_functions/userenv.adoc[userenv]
+**** xref:master/oracle_builtin_functions/rawtohex.adoc[rawtohex]
 *** xref:master/gb18030.adoc[国标GB18030]
 * 参考指南
 ** xref:master/tools_reference.adoc[工具参考]

CN/modules/ROOT/pages/master/oracle_builtin_functions/rawtohex.adoc

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+
+:sectnums:
+:sectnumlevels: 5
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+= **功能概述**
+
+IvorySQL提供兼容Oracle内置函数 ```RAWTOHEX('parameter')``` ，用于将RAW类型转换成十六进制字符串。
+
+== 实现原理
+
+PostgreSQL 提供的pg_catalog.encode(bytea, 'hex')函数，可直接完成二进制到十六进制的转换。
+考虑到当前系统中已经存在的HEXTORAW函数通过封装pg_catalog.decode 的SQL方式实现，本次开发的 
+RAWTOHEX 函数将使用相同的方式来实现，即使用 SQL 函数包装 PostgreSQL 内置函数pg_catalog.encode，
+而非编写 C 扩展。
+
+raw、text、bytea以及varchar2这四种类型做为输入需要被支持。
+sys.raw 是 bytea 的 domain 类型（typtype = 'd'，typbasetype = bytea），PostgreSQL 支持 domain 到 base type 的隐式转换，RAWTOHEX(bytea) 可自动接受 sys.raw 输入。
+sys.oravarcharchar（即 varchar2）到 pg_catalog.text 存在 IMPLICIT cast（datatype--1.0.sql），RAWTOHEX(text) 可自动接受 varchar2 输入。
+因此，定义两个重载（而不是四个）。
+
+```
+sys.rawtohex(bytea)  RETURNS varchar2
+sys.rawtohex(text)   RETURNS varchar2
+```
+
+具体功能则是在 `builtin_functions--1.0.sql` 中实现。
+```sql
+/* support rawtohex function for oracle compatibility */
+CREATE OR REPLACE FUNCTION sys.rawtohex(bytea)
+RETURNS varchar2
+AS $$ SELECT CASE WHEN pg_catalog.octet_length($1) > 0 THEN upper(pg_catalog.encode($1, 'hex'))::varchar2 END; $$ 
+LANGUAGE SQL
+PARALLEL SAFE
+STRICT
+IMMUTABLE;
+
+CREATE OR REPLACE FUNCTION sys.rawtohex(text)
+RETURNS varchar2
+AS $$ SELECT CASE WHEN pg_catalog.octet_length($1) > 0 THEN upper(pg_catalog.encode($1::bytea, 'hex'))::varchar2 END; $$ 
+LANGUAGE SQL
+PARALLEL SAFE
+STRICT
+IMMUTABLE;
+```
+
+== RAWTOHEX 典型用例
+[cols="8,2"]
+|====
+|*用例语句*|*返回值*
+|SELECT sys.rawtohex('\xDEADBEEF'::bytea); | DEADBEEF
+|SELECT sys.rawtohex('\xFF'::raw); | FF
+|SELECT sys.rawtohex('hello'::text); | 68656C6C6F
+|SELECT sys.rawtohex('hello'::varchar2); | 68656C6C6F
+|====

EN/modules/ROOT/nav.adoc

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 ** Built-in Functions
 *** xref:master/oracle_builtin_functions/sys_context.adoc[sys_context]
 *** xref:master/oracle_builtin_functions/userenv.adoc[userenv]
+*** xref:master/oracle_builtin_functions/rawtohex.adoc[rawtohex]
 ** xref:master/gb18030.adoc[GB18030 Character Set]
 * Reference
 ** xref:master/tools_reference.adoc[Tool Reference]

EN/modules/ROOT/pages/master/oracle_builtin_functions/rawtohex.adoc

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+= **Feature Overview**
+
+IvorySQL provides compatibility with Oracle's built-in function ```RAWTOHEX('parameter')```, which is used to convert RAW to a character value containing its hexadecimal representation.   
+
+== Implementation Principle
+
+The function pg_catalog.encode(bytea, 'hex') provided by PostgreSQL can directly convert binary data to hexadecimal.
+
+Given that the existing HEXTORAW function in the current system is implemented by wrapping pg_catalog.decode using SQL, the RAWTOHEX function developed this time will be implemented in the same way. That is, it will be a SQL function wrapping the PostgreSQL built-in function pg_catalog.encode, rather than implementing it via a C extension.
+
+The following four types need to be supported as input: raw, text, bytea, and varchar2.
+
+sys.raw is a domain type of bytea (typtype = 'd', typbasetype = bytea). PostgreSQL supports implicit conversion from a domain type to its base type, so RAWTOHEX(bytea) can automatically accept sys.raw as input.
+
+There is an IMPLICIT cast from sys.oravarcharchar (i.e., varchar2) to pg_catalog.text (defined in datatype--1.0.sql), so RAWTOHEX(text) can automatically accept varchar2 as input.
+
+Therefore, two overloaded versions (rather than four) will be defined.
+
+```
+sys.rawtohex(bytea)  RETURNS varchar2
+sys.rawtohex(text)   RETURNS varchar2
+```
+
+The specific functionality is implemented in builtin_functions—1.0.sql. 
+```sql
+/* support rawtohex function for oracle compatibility */
+CREATE OR REPLACE FUNCTION sys.rawtohex(bytea)
+RETURNS varchar2
+AS $$ SELECT CASE WHEN pg_catalog.octet_length($1) > 0 THEN upper(pg_catalog.encode($1, 'hex'))::varchar2 END; $$ 
+LANGUAGE SQL
+PARALLEL SAFE
+STRICT
+IMMUTABLE;
+
+CREATE OR REPLACE FUNCTION sys.rawtohex(text)
+RETURNS varchar2
+AS $$ SELECT CASE WHEN pg_catalog.octet_length($1) > 0 THEN upper(pg_catalog.encode($1::bytea, 'hex'))::varchar2 END; $$ 
+LANGUAGE SQL
+PARALLEL SAFE
+STRICT
+IMMUTABLE;
+```
+
+== RAWTOHEX use cases
+[cols="8,2"]
+|====
+|*SQL statement *|*return value*
+|SELECT sys.rawtohex('\xDEADBEEF'::bytea); | DEADBEEF
+|SELECT sys.rawtohex('\xFF'::raw); | FF
+|SELECT sys.rawtohex('hello'::text); | 68656C6C6F
+|SELECT sys.rawtohex('hello'::varchar2); | 68656C6C6F
+|====