Document the new string functions

[hengm3467]

Related code PR

risingwavelabs/risingwave#8767

Which part(s) of the docs might be affected or should be updated? And how?

SQL - Functions - String

Please experiment with creating docs for these functions using chatGPT

Adds the following functions:

chr(integer) -> varchar
starts_with(varchar, varchar) -> boolean
initcap(varchar) -> varchar
lpad(varchar, integer) -> varchar
lpad(varchar, integer, varchar) -> varchar
rpad(varchar, integer) -> varchar
rpad(varchar, integer, varchar) -> varchar
reverse(varchar) -> varchar
strpos(varchar, varchar) -> integer
to_ascii(varchar) -> varchar
to_hex(integer) -> varchar
to_hex(bigint) -> varchar

Reference

Please reference PG's docs for these string functions.

[xiangjinwu]

Let's hold on this until next version, as we have found several bugs in them

• fix(expr): fix lpad and rpad on empty fill string risingwave#8970
• fix(expr): align position syntax and strpos semantic with SQL standard risingwave#9000
• fix(expr): support multibyte Unicode for overlay and ascii risingwave#9321

[CharlieSYH]

@bernscode Please continue to update this doc PR as these code PRs are merged for 0.19.0:
risingwavelabs/risingwave#8970
risingwavelabs/risingwave#9000

[xiangjinwu]

FYI known issues have been fixed. They should be good to go in v0.19.0.