postgres search in column with escapes - postgresql

Question

Is there a way to do something like a grep for "site" from the following select (so that only "site=*" is returned from thedata)?
rr=# select thename,encode(thedata, 'escape') from
management_data.datas limit 2;
thename | thedata
-----------------------------------------------------------------------------------
Alexander | #
+
| #Fri Mar 15 14:58:18 PDT 2014
+
| BUs=ALL
+
| site=33$36$354$380$357$360$36$353$36$38$39$34$31$355
+
Anthony | #
+
| #Mon Jan 05 13:33:00 PST 2015
+
| mem=12000
+
| site=50$5$1$50
+
|

Answer 1

Given test data round-tripped successfully:
WITH somerow(name, blobofgarble) AS (
SELECT
TEXT 'Alexander',
BYTEA E'#\n#Fri Mar 15 14:58:18 PDT 2014\nBUs=ALL\nsite=33$36$354$380$357$360$36$353$36$38$39$34$31$355\n'
)
SELECT name, encode(blobofgarble, 'escape') FROM somerow;
Now, I can't possibly imagine why you'd store this information as bytea not a text field, but ... well, I guess there must be a reason. I'm going to rely on the simplifying assumption that the data, when escaped, can be treated as fairly sanely formed text, since otherwise the whole concept of "lines" is garbage and your question makes no sense.
With that assumption it's possible to use regexp_split_to_table to split on newlines, getting somewhat more sanely formed data:
WITH (...)
SELECT name, garblepart FROM somerow, regexp_split_to_table(encode(blobofgarble, 'escape'), E'\n') AS garblepart;
name | garblepart
-----------+------------------------------------------------------
Alexander | #
Alexander | #Fri Mar 15 14:58:18 PDT 2014
Alexander | BUs=ALL
Alexander | site=33$36$354$380$357$360$36$353$36$38$39$34$31$355
Alexander |
(5 rows)
(this is an implicit LATERAL query, so it'll only work in PostgreSQL 9.3 and above).
Now you can use pretty ordinary operations to find the row of interest and extract the desired part, in this case with some more pattern matching:
WITH (...)
SELECT
name, substring(garblepart from '=(.*$)')
FROM somerow,
regexp_split_to_table(encode(blobofgarble, 'escape'), E'\n') AS garblepart
WHERE garblepart LIKE 'site=%';
name | substring
-----------+-------------------------------------------------
Alexander | 33$36$354$380$357$360$36$353$36$38$39$34$31$355
(1 row)
Now go fix your schema so that you store your data sanely and don't have to do this.