"sumit kumar" <talk2mitsu@googlemail.com> writes:
> Can any1 please please help me know how pgsql estimates the cardinality of
> LIKE operator ??
See patternsel() and subsidiary routines in
http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/selfuncs.c
for whichever version you are interested in. (This code has changed
often enough that there's no version-independent answer to your
question.)
regards, tom lane