Rueian rueian
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| postgres=# select oid, oprname, oprcode, oprrest from pg_operator where oprname = '~~'; | |
| oid | oprname | oprcode | oprrest | |
| - - - + - - - - -+ - - - - - - + - - - - - | |
| 1207 | ~~ | namelike | likesel | |
| 1209 | ~~ | textlike | likesel | |
| 1211 | ~~ | bpcharlike | likesel | |
| 2016 | ~~ | bytealike | likesel | |
| (4 rows) |
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| postgres=# select oid, proname, prosrc from pg_proc where oid = (select distinct oprrest from pg_operator where oprname = '~~'); | |
| oid | proname | prosrc | |
| - - - + - - - - -+ - - - - - | |
| 1819 | likesel | likesel | |
| (1 row) |
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| if (pstatus == Pattern_Prefix_Exact) | |
| { | |
| /* | |
| * Pattern specifies an exact match, so estimate as for '=' | |
| */ | |
| result = var_eq_const(&vardata, eqopr, prefix->constvalue, | |
| false, true, false); | |
| } |
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| selec = histogram_selectivity(&vardata, &opproc, constval, true, | |
| 10, 1, &hist_size); | |
| /* If not at least 100 entries, use the heuristic method */ | |
| if (hist_size < 100) | |
| { | |
| Selectivity heursel; | |
| Selectivity prefixsel; |
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| *hist_size = sslot.nvalues; | |
| if (sslot.nvalues >= min_hist_size) | |
| { | |
| int nmatch = 0; | |
| int i; | |
| for (i = n_skip; i < sslot.nvalues - n_skip; i++) | |
| { | |
| if (varonleft ? | |
| DatumGetBool(FunctionCall2Coll(opproc, |
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| /* If not at least 100 entries, use the heuristic method */ | |
| if (hist_size < 100) | |
| { | |
| Selectivity heursel; | |
| Selectivity prefixsel; | |
| if (pstatus == Pattern_Prefix_Partial) | |
| prefixsel = prefix_selectivity(root, &vardata, | |
| eqopr, ltopr, geopr, | |
| prefix); |
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| static Selectivity | |
| prefix_selectivity(PlannerInfo *root, VariableStatData *vardata, | |
| Oid eqopr, Oid ltopr, Oid geopr, | |
| Const *prefixcon) | |
| { | |
| Selectivity prefixsel; | |
| FmgrInfo opproc; | |
| AttStatsSlot sslot; | |
| Const *greaterstrcon; | |
| Selectivity eq_sel; |
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| /* | |
| * Pull out any fixed prefix implied by the pattern, and estimate the | |
| * fractional selectivity of the remainder of the pattern. Unlike many | |
| * other selectivity estimators, we use the pattern operator's actual | |
| * collation for this step. This is not because we expect the collation | |
| * to make a big difference in the selectivity estimate (it seldom would), | |
| * but because we want to be sure we cache compiled regexps under the | |
| * right cache key, so that they can be re-used at runtime. | |
| */ | |
| patt = (Const *) other; |
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| /* | |
| * Estimate the selectivity of a pattern of the specified type. | |
| * Note that any fixed prefix of the pattern will have been removed already, | |
| * so actually we may be looking at just a fragment of the pattern. | |
| * | |
| * For now, we use a very simplistic approach: fixed characters reduce the | |
| * selectivity a good deal, character ranges reduce it a little, | |
| * wildcards (such as % for LIKE or .* for regex) increase it. | |
| */ |
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| /* In any case, don't believe extremely small or large estimates. */ | |
| if (selec < 0.0001) | |
| selec = 0.0001; | |
| else if (selec > 0.9999) | |
| selec = 0.9999; |