Question: how are substrings of size 1 or 2 handled? Are they just ignored? 

explain analyze
select * from azjunk7n where txt ~ 'ba'; -- '~' means: consider regex 
+index

                                                     QUERY PLAN       
+                                               
----------------------------------------------------------------------
+-----------------------------------------------
 Seq Scan on azjunk7n  (cost=0.00..267879.16 rows=707066 width=85) (ac
+tual time=5.413..9163.252 rows=897633 loops=1)
   Filter: (txt ~ 'ba'::text)
   Rows Removed by Filter: 9102367
 Planning Time: 0.360 ms
 Execution Time: 9189.173 ms
(5 rows)

Time: 9190.029 ms (00:09.190)

[download]

Nine seconds. Because, of course, if there are too many hits (here: 897633), the system switches to SeqScan - after all, a sequential scan is the fastest way to access many rows. Faster would've been: where position('ba' in txt) > 0 which would SeqScan in 3 seconds; but position() doesn't allow regexen.

In reply to Re^6: Documentation of REGEXP support in DBD::SQLite? by erix
in thread Documentation of REGEXP support in DBD::SQLite? by ibm1620

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