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 CREATE_OPTIONS
def test t1 f1 1 NULL YES char 1 2 NULL NULL NULL ucs2 ucs2_uca1400_ai_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_uca1400_ai_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_uca1400_ai_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_uca1400_ai_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_uca1400_ai_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_uca1400_ai_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_uca1400_ai_ci
2.0000 varchar ucs2 ucs2_uca1400_ai_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_uca1400_ai_ci
NULL varchar ucs2 ucs2_uca1400_ai_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_uca1400_ai_ci char(1)
NULL test t1 f2 char 0 0 ucs2 ucs2_uca1400_ai_ci char(0)
2.0000 test t1 f3 char 10 20 ucs2 ucs2_uca1400_ai_ci char(10)
NULL test t1 f5 varchar 0 0 ucs2 ucs2_uca1400_ai_ci varchar(0)
2.0000 test t1 f6 varchar 255 510 ucs2 ucs2_uca1400_ai_ci varchar(255)
2.0000 test t1 f7 varchar 260 520 ucs2 ucs2_uca1400_ai_ci varchar(260)
DROP TABLE t1;