I have been observing a case where the row count estimation for LIKE 'foo' is (much) higher than for LIKE 'foo%', the rest of the query being the same. This is a special case of the estimation for equality being higher than for a range query that includes the value used in the equality.
I haven't been able to get a copy of the data from the client yet, but considering the nature of the data and the description of the selectivity estimation algorithms (http://www.postgresql.org/docs/8.3/static/row-estimation-examples.html), this behavior appears to be mathematically plausible. I have been wondering whether in general the eqsel should try to compare its result with the estimation of (x >= 'foo' AND x <= 'foo') and use that as a ceiling or something. Has anyone else observed something similar? -- Peter Eisentraut http://developer.postgresql.org/~petere/ ---------------------------(end of broadcast)--------------------------- TIP 2: Don't 'kill -9' the postmaster
