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MCOL-271 empty strings should not be NULLs (#2794)

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This patch improves handling of NULLs in textual fields in ColumnStore.
Previously empty strings were considered NULLs and it could be a problem
if data scheme allows for empty strings. It was also one of major
reasons of behavior difference between ColumnStore and other engines in
MariaDB family.

Also, this patch fixes some other bugs and incorrect behavior, for
example, incorrect comparison for "column <= ''" which evaluates to
constant True for all purposes before this patch.
This commit is contained in:
Sergey Zefirov
2023-03-30 17:26:45 +01:00
committed by Roman Nozdrin
parent 0ea592da80
commit b53c231ca6
417 changed files with 12459 additions and 3520 deletions
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77
mysql-test/columnstore/basic/r/mcol271-empty-string-is-not-null.result Normal file
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DROP DATABASE IF EXISTS test_empty_strings;
CREATE DATABASE test_empty_strings;
USE test_empty_strings;
CREATE TABLE t(s text) ENGINE=COLUMNSTORE;
INSERT INTO t(s) VALUES (''), (NULL);
SELECT COUNT(*) FROM t WHERE s IS NULL;
COUNT(*)
1
SELECT COUNT(*) FROM t WHERE s IS NOT NULL;
COUNT(*)
1
SELECT * FROM t;
s
NULL
DROP TABLE t;
CREATE TABLE t(s text) ENGINE=COLUMNSTORE;
INSERT INTO t(s) VALUES ('');
INSERT INTO t(s) VALUES (NULL);
SELECT * FROM t;
s
NULL
SELECT COUNT(*) FROM t WHERE s IS NULL;
COUNT(*)
1
DROP TABLE t;
CREATE TABLE t(s text) ENGINE=COLUMNSTORE;
INSERT INTO t(s) VALUES ('_CpNuLl_'),(''), (NULL);
SELECT * FROM t;
s
_CpNuLl_
NULL
SELECT COUNT(*) FROM t WHERE s IS NULL;
COUNT(*)
1
DROP TABLE t;
CREATE TABLE t(c6 CHAR(6)) ENGINE=COLUMNSTORE;
INSERT INTO t(c6) VALUES ('a'), ('b'), ('c');
SELECT 2, COUNT(*) FROM t WHERE (c6 <= 'b' OR c6 <= '');
2 COUNT(*)
2 2
SELECT 2, COUNT(*) FROM t WHERE (c6 <= 'b');
2 COUNT(*)
2 2
SELECT 0, COUNT(*) FROM t WHERE (c6 <= '');
0 COUNT(*)
0 0
SELECT 0, COUNT(*) FROM t WHERE (c6 <= ' ');
0 COUNT(*)
0 0
SELECT 2, COUNT(*) FROM t WHERE (c6 <= 'b' OR c6 <= ' ');
2 COUNT(*)
2 2
SELECT 0, COUNT(*) FROM t WHERE (c6 < '');
0 COUNT(*)
0 0
SELECT 0, COUNT(*) FROM t WHERE (c6 < ' ');
0 COUNT(*)
0 0
DROP TABLE IF EXISTS t;
CREATE TABLE t(a CHAR(10)) ENGINE=COLUMNSTORE;
INSERT INTO t(a) VALUES (''), (NULL), (' '), (' a ');
SELECT LTRIM_ORACLE(a) FROM t;
LTRIM_ORACLE(a)
NULL
NULL
NULL
a
SELECT RTRIM_ORACLE(a) FROM t;
RTRIM_ORACLE(a)
NULL
NULL
NULL
a
DROP DATABASE test_empty_strings;