Add String Contains Another String as a postgres til.

postgres/string-contains-another-string.md

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+# String Contains Another String
+
+You can check if a string *contains* another string using the `position`
+function.
+
+```sql
+> select position('One' in 'One Two Three');
+ position
+----------
+        1
+```
+
+It returns the 1-based index of the first character of the first match of
+that substring.
+
+```sql
+> select position('Four' in 'One Two Three');
+ position
+----------
+        0
+```
+
+If the substring doesn't appear within the string, then the result is 0.
+
+Thus, you can determine if a string *contains* another string by checking if
+the value resulting from `position` is greater than 0.