Add Pdo abstraction layer

[glensc]

To handle:

• different identifier quote style for tables/columns
• sqlite: double quote
• pgsql: double quote
• mysql: backtick
• LIMIT operand: PdoSearcher: Use portable LIMIT/OFFSET #335
• sqlite: LIMIT row_to_skip, row_count
• mysql: LIMIT row_to_skip, row_count
• pgsql: LIMIT row_count OFFSET row_to_skip

A solution for #322

[glensc]

@perftools/maintainers perhaps it's better to use existing abstraction, than invent our own?

same question asked earlier:

• PDO integration is rough #322 (comment)

Some choices:

• https://github.com/doctrine/dbal
• https://github.com/cakephp/database

the different pdo drivers need different approaches, see notes from #322

WDYT?

[lauripiisang]

Doesn't https://www.php.net/manual/en/pdo.quote.php help you achieve the same thing?

PDO::quote() places quotes around the input string (if required) and escapes special characters within the input string, using a quoting style appropriate to the underlying driver.

[glensc]

@lauripiisang, unfortunately, no, quote() is for values quoting ("a\""), but here need to quote identifiers (table names, column names).

in mysql identifiers are quoted with backticks and values with backslash. other systems use double quotes for identifiers and double quotes for an enoding double quote inside double quote separated value: """" is a double quote. actually mysql supports this encode style too.

[glensc]

so to cut story short: can't reliably quote column "get" in these pdo drivers:

• pgsql
• mysql
• sqlite

mysql example included:

15:13:36 mysql{2}> select get;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'get' at line 1
15:15:31 mysql{3}> select `get`;
ERROR 1054 (42S22): Unknown column 'get' in 'field list'
15:15:35 mysql{4}> select "get";
+-----+
| get |
+-----+
| get |
+-----+
1 row in set (0.00 sec)

15:15:45 mysql{5}>

[lauripiisang]

sorry, missed that it was about quoting identifiers . yeah, that's unfortunate separate story.

[lauripiisang]

According to https://stackoverflow.com/questions/214309/do-different-databases-use-different-name-quote/214344#214344

The standard SQL language uses double-quotes for delimited identifiers

MySQL uses back-quotes by default. MySQL can use standard double-quotes:

SELECT * FROM `my table`;
SET SQL_MODE=ANSI_QUOTES;
SELECT * FROM "my table";

Maybe it's possible to drop backticks in favor of "ansi quotes" ?

[glensc]

that's a good find!

also need to quote the column named GET, seems it suits there as well, not selecting a string:

15:03:49 mysql{1}> SET SQL_MODE=ANSI_QUOTES;
Query OK, 0 rows affected, 1 warning (0.03 sec)

Warning (Code 3090): Changing sql mode 'NO_AUTO_CREATE_USER' is deprecated. It will be removed in a future release.
15:03:50 mysql{2}> select "GET";
ERROR 1054 (42S22): Unknown column 'GET' in 'field list'
15:03:55 mysql{3}>

[glensc]

good thing is that it works as low as mysql 5.0:

15:06:00 mysql@192.168.40.12:1> SET SQL_MODE=ANSI_QUOTES;
Query OK, 0 rows affected (0.00 sec)

15:06:06 mysql@192.168.40.12:2> select "GET";
ERROR 1054 (42S22): Unknown column 'GET' in 'field list'
15:06:11 mysql@192.168.40.12:3> select @@version;
+------------+
| @@version  |
+------------+
| 5.0.96-log |
+------------+
1 row in set (0.00 sec)

[glensc]

#336

altho maybe acceptable solution would had also been to rename "GET" column to to something else, and leave upgrade notitice that the column must be renamed when upgrading.

[lauripiisang]

yeah, I suppose that would be easier and less-hacky. reserved words probably should be avoided.

[glensc]

the thing is that reserved new reserved words can appear.

stupid solution to that is to prefix all columns and tables with xhgui :)

[lauripiisang]

as for limit and offset,

LIMIT x OFFSET y should be valid SQL regardless of engine

[glensc]

Fix limit: #335

I knew mysql suports LIMIT x OFFSET y, wasn't sure about sqlite, and didn't search for actual SQL specification to get confidence.

[glensc]

added PoC with needed changes to use quoteIdentifier.

it really looks like building another abstraction layer here...

[glensc]

superseded by #336