Error in DESCRIBE PLAN SELECT COUNT(*) FROM table on running server

[nicktobey]

Connecting to a running server and running a query of the form DESCRIBE PLAN SELECT COUNT(*) FROM table results in an error:

Error 1105 (HY000): result max1Row iterator returned more than one row

This only happens when connecting to a server, and not when running dolt sql locally.

This seems to be happening because the presence of the COUNT expression causes the analyzer to set the sql.QFlagMax1Row flag, but the DESCRIBE statement produces a row for each line in the plan.

[macneale4]

This is a more general bug:

You can recreate with:

CREATE TABLE mytable1 (
  id INT AUTO_INCREMENT PRIMARY KEY,
  str VARCHAR(255),
  num INT
);
CREATE TABLE mytable2 (
  id INT AUTO_INCREMENT PRIMARY KEY,
  str VARCHAR(255),
  num INT
);
INSERT INTO mytable1 (str, num) VALUES
('abc', 123);
INSERT INTO mytable2 (str, num) VALUES
('def', 456);
CALL dolt_add('.');
CALL dolt_commit('-m', 'my commit');

SELECT *
FROM dolt_diff
WHERE commit_hash = '<commit_hash>'
AND table_name LIKE 'mytable%';

(commit ID is the commit created in first step).

Note that this only happens when running in a sql-server - won't happen if you run dolt sql on your datadir.

[timsehn]

This effects a user. It will be fixed today.

[nicktobey]

The issues, while related, were different. In both cases the QFlagMax1Row flag was improperly set, but for different reasons.

The bug that @macneale4 reported was fixed with dolthub/go-mysql-server#2868.

The original query described in this issue is still not working, but isn't affecting users. I'll keep this issue open to track the original bug.