SET @@session.sql_mode = 'NO_ENGINE_SUBSTITUTION';
USE test;
DROP TABLE IF EXISTS t1;
CREATE TABLE t1
(
f1 CHAR         UNICODE,
f2 CHAR(0)      UNICODE,
f3 CHAR(10)     UNICODE,
f5 VARCHAR(0)   UNICODE,
f6 VARCHAR(255) UNICODE,
f7 VARCHAR(260) UNICODE
) ENGINE = MEMORY;
SELECT * FROM information_schema.columns
WHERE table_schema LIKE 'test%'
ORDER BY table_schema, table_name, column_name;
TABLE_CATALOG	TABLE_SCHEMA	TABLE_NAME	COLUMN_NAME	ORDINAL_POSITION	COLUMN_DEFAULT	IS_NULLABLE	DATA_TYPE	CHARACTER_MAXIMUM_LENGTH	CHARACTER_OCTET_LENGTH	NUMERIC_PRECISION	NUMERIC_SCALE	DATETIME_PRECISION	CHARACTER_SET_NAME	COLLATION_NAME	COLUMN_TYPE	COLUMN_KEY	EXTRA	PRIVILEGES	COLUMN_COMMENT	IS_GENERATED	GENERATION_EXPRESSION	IS_SYSTEM_TIME_PERIOD_START	IS_SYSTEM_TIME_PERIOD_END
def	test	t1	f1	1	NULL	YES	char	1	2	NULL	NULL	NULL	ucs2	ucs2_general_ci	char(1)			select,insert,update,references		NEVER	NULL	NO	NO
def	test	t1	f2	2	NULL	YES	char	0	0	NULL	NULL	NULL	ucs2	ucs2_general_ci	char(0)			select,insert,update,references		NEVER	NULL	NO	NO
def	test	t1	f3	3	NULL	YES	char	10	20	NULL	NULL	NULL	ucs2	ucs2_general_ci	char(10)			select,insert,update,references		NEVER	NULL	NO	NO
def	test	t1	f5	4	NULL	YES	varchar	0	0	NULL	NULL	NULL	ucs2	ucs2_general_ci	varchar(0)			select,insert,update,references		NEVER	NULL	NO	NO
def	test	t1	f6	5	NULL	YES	varchar	255	510	NULL	NULL	NULL	ucs2	ucs2_general_ci	varchar(255)			select,insert,update,references		NEVER	NULL	NO	NO
def	test	t1	f7	6	NULL	YES	varchar	260	520	NULL	NULL	NULL	ucs2	ucs2_general_ci	varchar(260)			select,insert,update,references		NEVER	NULL	NO	NO
##########################################################################
# Show the quotient of CHARACTER_OCTET_LENGTH and CHARACTER_MAXIMUM_LENGTH
##########################################################################
SELECT DISTINCT
CHARACTER_OCTET_LENGTH / CHARACTER_MAXIMUM_LENGTH AS COL_CML,
DATA_TYPE,
CHARACTER_SET_NAME,
COLLATION_NAME
FROM information_schema.columns
WHERE table_schema LIKE 'test%'
AND CHARACTER_OCTET_LENGTH / CHARACTER_MAXIMUM_LENGTH = 1
ORDER BY CHARACTER_SET_NAME, COLLATION_NAME, COL_CML;
COL_CML	DATA_TYPE	CHARACTER_SET_NAME	COLLATION_NAME
SELECT DISTINCT
CHARACTER_OCTET_LENGTH / CHARACTER_MAXIMUM_LENGTH AS COL_CML,
DATA_TYPE,
CHARACTER_SET_NAME,
COLLATION_NAME
FROM information_schema.columns
WHERE table_schema LIKE 'test%'
AND CHARACTER_OCTET_LENGTH / CHARACTER_MAXIMUM_LENGTH <> 1
ORDER BY CHARACTER_SET_NAME, COLLATION_NAME, COL_CML;
COL_CML	DATA_TYPE	CHARACTER_SET_NAME	COLLATION_NAME
2.0000	char	ucs2	ucs2_general_ci
2.0000	varchar	ucs2	ucs2_general_ci
SELECT DISTINCT
CHARACTER_OCTET_LENGTH / CHARACTER_MAXIMUM_LENGTH AS COL_CML,
DATA_TYPE,
CHARACTER_SET_NAME,
COLLATION_NAME
FROM information_schema.columns
WHERE table_schema LIKE 'test%'
AND CHARACTER_OCTET_LENGTH / CHARACTER_MAXIMUM_LENGTH IS NULL
ORDER BY CHARACTER_SET_NAME, COLLATION_NAME, COL_CML;
COL_CML	DATA_TYPE	CHARACTER_SET_NAME	COLLATION_NAME
NULL	char	ucs2	ucs2_general_ci
NULL	varchar	ucs2	ucs2_general_ci
--> CHAR(0) is allowed (see manual), and here both CHARACHTER_* values
--> are 0, which is intended behavior, and the result of 0 / 0 IS NULL
SELECT CHARACTER_OCTET_LENGTH / CHARACTER_MAXIMUM_LENGTH AS COL_CML,
TABLE_SCHEMA,
TABLE_NAME,
COLUMN_NAME,
DATA_TYPE,
CHARACTER_MAXIMUM_LENGTH,
CHARACTER_OCTET_LENGTH,
CHARACTER_SET_NAME,
COLLATION_NAME,
COLUMN_TYPE
FROM information_schema.columns
WHERE table_schema LIKE 'test%'
ORDER BY TABLE_SCHEMA, TABLE_NAME, ORDINAL_POSITION;
COL_CML	TABLE_SCHEMA	TABLE_NAME	COLUMN_NAME	DATA_TYPE	CHARACTER_MAXIMUM_LENGTH	CHARACTER_OCTET_LENGTH	CHARACTER_SET_NAME	COLLATION_NAME	COLUMN_TYPE
2.0000	test	t1	f1	char	1	2	ucs2	ucs2_general_ci	char(1)
NULL	test	t1	f2	char	0	0	ucs2	ucs2_general_ci	char(0)
2.0000	test	t1	f3	char	10	20	ucs2	ucs2_general_ci	char(10)
NULL	test	t1	f5	varchar	0	0	ucs2	ucs2_general_ci	varchar(0)
2.0000	test	t1	f6	varchar	255	510	ucs2	ucs2_general_ci	varchar(255)
2.0000	test	t1	f7	varchar	260	520	ucs2	ucs2_general_ci	varchar(260)
DROP TABLE t1;