Hi,
While playing with pg_plan_advice, I noticed another small issue.
Each FOREIGN_JOIN target sublist must contain at least two relation
identifiers, as the error message states:
```
evantest=# SET pg_plan_advice.advice = 'FOREIGN_JOIN((x))';
ERROR: invalid value for parameter "pg_plan_advice.advice": "FOREIGN_JOIN((x))"
DETAIL: Could not parse advice: FOREIGN_JOIN targets must contain more than
one relation identifier at or near ")"
```
However, it silently accepts an empty sublist:
```
evantest=# SET pg_plan_advice.advice = 'FOREIGN_JOIN(())';
SET
```
The problem is that, the parser currently checks whether the sublist length is
== 1, rather than < 2:
```
if ($$->tag == PGPA_TAG_FOREIGN_JOIN)
{
foreach_ptr(pgpa_advice_target, target, $3)
{
if (target->ttype ==
PGPA_TARGET_IDENTIFIER ||
list_length(target->children)
== 1)
pgpa_yyerror(result,
parse_error_msg_p, yyscanner,
"FOREIGN_JOIN targets must contain more than one relation identifier");
}
}
```
So the fix is simply to change == 1 to < 2. With the fix, FOREIGN_JOIN(()) is
rejected:
```
evantest=# SET pg_plan_advice.advice = 'FOREIGN_JOIN(())';
ERROR: invalid value for parameter "pg_plan_advice.advice": "FOREIGN_JOIN(())"
DETAIL: Could not parse advice: FOREIGN_JOIN targets must contain more than
one relation identifier at or near ")"
```
FOREIGN_JOIN() is still accepted. As documented in the opening comments of
syntax.sql, empty target lists are allowed for most advice tags, except
JOIN_ORDER:
```
-- An empty string is allowed. Empty target lists are allowed for most advice
-- tags, but not for JOIN_ORDER. "Supplied Plan Advice" should be omitted in
-- text format when there is no actual advice, but not in non-text format.
```
Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/
