ltrim returns a copy of subsequence of string str with all the characters present in trimchars trimmed off from the beginning. If the second argument is omitted, it is a space ' ' by default.
rtrim is similar except that it trims from the right.
trim trims from both ends.
concat('*',trim(' SIMURG '),'*') -> '*SIMURG*'
ltrim('AbracadabrA','bAr') -> 'acadabrA'
rtrim('AbracadabrA','bAr') -> 'Abracada'
trim('AbracadabrA','bAr') -> 'acada'