Implement SQL String functions with documentations

[AmrDeveloper]

Implement string function in our engine, one per pull request.

Steps:

• Choose unimplemented function and write I am on <function_name>.
• Then start implement the function in crates/gitql-ast/function.rs.
• Add docs for it in docs/function/function.md.
• Make sure everything is formatted and submit a Pull Request.
• Don't forget to mention issue number in pull request title.

Text Functions

• [x] ASCII
• [x] CHAR
• [x] CHARINDEX
• [x] CONCAT
• [x] DATALENGTH
• [ ] DIFFERENCE
• [ ] FORMAT
• [x] LEFT
• [x] LEN
• [x] LOWER
• [x] LTRIM
• [x] NCHAR
• [ ] PATINDEX
• [x] QUOTENAME
• [x] REPLACE
• [x] REPLICATE
• [x] REVERSE
• [x] RIGHT
• [x] RTRIM
• [x] SOUNDEX
• [x] SPACE
• [ ] STR
• [x] STUFF
• [x] SUBSTRING
• [x] TRANSLATE
• [x] TRIM
• [x] UNICODE
• [x] UPPER

For more information about implementation and description check https://www.w3schools.com/sql/sql_ref_sqlserver.asp

Note: You can only open max 3 PR at the time

[Lilit0x]

I am on ASCII

[Lilit0x]

I am on CHAR

[Lilit0x]

@AmrDeveloper , the CHARINDEX function might be tricky since the last argument is optional, but the condition checks if the specified arguments match, I mean here .

[Lilit0x]

I am on DATALENGTH. Also, you made a typo for DATALENGTH in the list

[AmrDeveloper]

@AmrDeveloper , the CHARINDEX function might be tricky since the last argument is optional, but the condition checks if the specified arguments match, I mean here .

You are right some functions we will delay them until do some improvements in type system

[Lilit0x]

I am on LEFT

[Lilit0x]

@AmrDeveloper, is there a difference between the implementation of NCHAR and CHAR at least in Rust, since all characters are just u32s under the hood and just casting from the number will be the same.

[AmrDeveloper]

NCHAR

You are right, we can ignore it for now and maybe if needed we can pass the the char function to it

[Lilit0x]

NCHAR

You are right, we can ignore it for now and maybe if needed we can pass the the char function to it

Yeahh, that was I planned on doing, wanted to get your approval on it.

[Lilit0x]

I am on PATINDEX

[AmrDeveloper]

NCHAR

You are right, we can ignore it for now and maybe if needed we can pass the the char function to it

Yeahh, that was I planned on doing, wanted to get your approval on it.

I faced the same problem in Date functions too we need to decide if we should duplicate them or take only one

[Lilit0x]

NCHAR

You are right, we can ignore it for now and maybe if needed we can pass the the char function to it

Yeahh, that was I planned on doing, wanted to get your approval on it.

I faced the same problem in Date functions too we need to decide if we should duplicate them or take only one

We could just use different names for them but they'll still be the same function. What I mean is:

  map.insert("char", text_char);
  map.insert("nchar", text_char);

And we do the same in the PROTOTYPES hashmap too

[Lilit0x]

I am on REPLACE

[Lilit0x]

I am on RIGHT

[Lilit0x]

I am on STUFF

[Lilit0x]

I am on SUBSTRING

[Lilit0x]

I am on TRANSLATE

[AmrDeveloper]

@Lilit0x Lets keep next PR one by one it will be fast to review and merge

[Lilit0x]

Okay, got it.

[Lilit0x]

I am on SOUNDEX

[tbro]

I am on CONCAT

[tbro]

I am on UNICODE

[mobley-trent]

I am on CHARINDEX

[mobley-trent]

Hello @AmrDeveloper how do we handle optional arguments ?

[AmrDeveloper]

@mobley-trent Optional type is not implemented yet, i just implemented Variant and will implement Option soon

[AmrDeveloper]

@mobley-trent Now support Optional and varargs types

[frectonz]

@AmrDeveloper NCHAR is already implemented but it's not marked as complete in the task list.

[frectonz]

I am on QUOTENAME