Add Lower Is Faster Than ilike as a postgres til

postgres/lower-is-faster-than-ilike.md

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+# Lower Is Faster Than ilike
+
+There are a couple ways to do a case-insensitive comparison of data in
+PostgreSQL. One way is to use the `ilike` operator for comparison. Another
+way is to use the `lower()` function on both sides of the `=` operator for
+comparison. Using `lower()` is a bit faster than using `ilike`.
+
+When comparing
+
+```sql
+select * from users where email ilike 'some-email@example.com';
+```
+
+to
+
+```sql
+select * from users where lower(email) = lower('some-email@example.com');
+```
+
+we find (via `explain analyze`) that using `lower()` was taking around 12ms
+where as the `ilike` example was taking around 17ms.
+
+We earn orders of magnitude in performance when adding a functional index
+that uses the `lower()` function like so:
+
+```sql
+create unique index users_unique_lower_email_idx on users (lower(email));
+```
+
+After adding this index, the example using `lower()` drops to around 0.08ms.
+
+For the full example and `explain analyze` outputs, [see this
+document](https://github.com/jbranchaud/postgresing/blob/master/ilike_vs_lower.sql).