On 12/07/2016 13:59, New, Cecil (GE Aviation, US) wrote:
The best I have been able to come with is documented at:
http://stackoverflow.com/questions/32640043/cannot-detect-cyclic-data-in-an-sqlite-database/32719216#32719216
But a) it is ugly, b) performance impact of all the length(), replace()
functions, c) if values end in similar strings, it probably won't work.
After some thought, I think the minimum that would solve this problem is to
enhance the instr() function to either take a starting position to begin the
search or to take an occurrence number to search for. Oracle's version of
instr() does both of these (see
https://docs.oracle.com/cd/B28359_01/olap.111/b28126/dml_functions_1103.htm)
Postgresql has a specific way of detecting loops, which would be even more
robust. It is documented here:
https://www.postgresql.org/docs/9.1/static/queries-with.html
Three suggestions to solve this problem are described in Section 24.4 of
the following document:
https://staff.info.unamur.be/dbm/Documents/Tutorials/SQLfast/SQLfast-Tuto24-Recursive-programming.pdf
Recursive triggers can be used as well (see Section 24.7).
J-L Hainaut
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