Fix escaping for some SHOW queries

[alesapin]

Changelog category (leave one):

• Bug Fix (user-visible misbehavior in an official stable release)

Changelog entry (a user-readable short description of the changes that goes into CHANGELOG.md):

Fix wrong escaping for SHOW COLUMNS and SHOW FUNCTIONS queries.

[clickhouse-gh]

Workflow [PR], commit [fabd077]

Summary: ❌

job_name	test_name	status	info	comment
BuzzHouse (amd_debug)		failure
	Buzzing result	failure	cidb
BuzzHouse (amd_tsan)		failure
	Buzzing result	failure	cidb
BuzzHouse (amd_ubsan)		failure
	Buzzing result	failure	cidb

[alexey-milovidov]

.

[alexey-milovidov]

With the SQLite database created on top of a prepared .sqlite3 file?

[alesapin]

@alexey-milovidov which query you need to write in clickhouse-client to trigger this logic? You cannot specify arbitrary string as table name.

[alexey-milovidov]

According to the code, it will be EXISTS TABLE from the SQLite database.

[alesapin]

@alexey-milovidov our parser will not allow you to type arbitrary string in EXISTS TABLE query, it parses identifiers:

alesapin-workstation :) exists table like '%aaa%'

Syntax error: failed at position 19 ('%aaa%'):

exists table like '%aaa%'

Expected one of: token, Dot, INTO OUTFILE, FORMAT, SETTINGS, ParallelWithClause, PARALLEL WITH, end of query

alesapin-workstation :) exists table '%aaa%'

Syntax error: failed at position 14 ('%aaa%'):

exists table '%aaa%'

Expected identifier

[alexey-milovidov]

Identifiers can be arbitrary non-empty strings.

[alexey-milovidov]

EXISTS TABLE sqlite."a'b''c\\'d\\"

[alexey-milovidov]

FYI, "Bugfix validation" shows that the new tests pass on the master branch. If it's not the case, ask our CI team.