On Tue, 25 Jan 2022 at 21:33, Ivan Panchenko <i.panche...@postgrespro.ru> wrote:
> > On 26.01.2022 00:21, benj....@laposte.net wrote: > > Le 25/01/2022 à 18:10, Shaozhong SHI a écrit : > >> There is a short of a function in the standard Postgres to do the > >> following: > >> > >> It is easy to count the number of occurrence of words, but it is > >> rather difficult to count the number of occurrence of phrases. > >> > >> For instance: > >> > >> A cell of value: 'Hello World' means 1 occurrence a phrase. > >> > >> A cell of value: 'Hello World World Hello' means no occurrence of any > >> repeated phrase. > >> > >> But, A cell of value: 'Hello World World Hello Hello World' means 2 > >> occurrences of 'Hello World'. > >> > >> 'The City of London, London' also has no occurrences of any repeated > >> phrase. > >> > >> Anyone has got such a function to check out the number of occurrence > >> of any repeated phrases? > >> > >> Regards, > >> > >> David > > > > Don't know if it's exactly what you want, but you can replace all > > occurence of the phrase in the text by empty string and compute the > > diff between the initial and the result and next divide by the length > > of your phrase. > > > > Example : > > WITH x AS (SELECT 'toto like tata and toto like titi and toto like > > tutu' , 'toto like' phrase) > > SELECT (char_length(texte) - char_length(replace(texte, phrase, ''))) > > / char_length(phrase) AS nb_occurence > > FROM x > > > This works if the user knows the phrase. As far as I understood, the > phrase is not known, and user wants to count number of repeats of any > phrases. > Of course this can be done with recursive CTE. Split into words, > generate all phrases (AFAIK requires recursion), then group and count. > > But probably in PL/Perl this could be done more effectively. > Is there an example of using recursive CTE to split a text string into words? Regards, David
