Information Schema COLUMNS Table

The Information Schema COLUMNS table provides information about columns in each table on the server.

It contains the following columns:

Column	Description
Column	Description
TABLE_CATALOG	Always contains the string 'def'.
TABLE_SCHEMA	Database name.
TABLE_NAME	Table name.
COLUMN_NAME	Column name.
ORDINAL_POSITION	Column position in the table. Can be used for ordering.
COLUMN_DEFAULT	Default value for the column. Literals are quoted to distinguish them from expressions. NULL means that the column has no default. In MariaDB 10.2.6 and earlier, no quotes were used for any type of default and NULL can either mean that there is no default, or that the default column value is NULL.
IS_NULLABLE	Whether the column can contain NULLs.
DATA_TYPE	The column's data type.
CHARACTER_MAXIMUM_LENGTH	Maximum length.
CHARACTER_OCTET_LENGTH	Same as the CHARACTER_MAXIMUM_LENGTH except for multi-byte character sets.
NUMERIC_PRECISION	For numeric types, the precision (number of significant digits) for the column. NULL if not a numeric field.
NUMERIC_SCALE	For numeric types, the scale (significant digits to the right of the decimal point). NULL if not a numeric field.
DATETIME_PRECISION	Fractional-seconds precision, or NULL if not a time data type.
CHARACTER_SET_NAME	Character set if a non-binary string data type, otherwise NULL.
COLLATION_NAME	Collation if a non-binary string data type, otherwise NULL.
COLUMN_TYPE	Column definition, a MySQL and MariaDB extension.
COLUMN_KEY	Index type. PRI for primary key, UNI for unique index, MUL for multiple index. A MySQL and MariaDB extension.
EXTRA	Additional information about a column, for example whether the column is an invisible column, or WITHOUT SYSTEM VERSIONING if the table is not a system-versioned table. A MySQL and MariaDB extension.
PRIVILEGES	Which privileges you have for the column. A MySQL and MariaDB extension.
COLUMN_COMMENT	Column comments.
IS_GENERATED	Indicates whether the column value is generated (virtual, or computed). Can be ALWAYS or NEVER.
GENERATION_EXPRESSION	The expression used for computing the column value in a generated (virtual, or computed) column.
IS_SYSTEM_TIME_PERIOD_START	From MariaDB 11.4.1.
IS_SYSTEM_TIME_PERIOD_END	From MariaDB 11.4.1.

It provides information similar to, but more complete, than SHOW COLUMNS and mariadb-show.

Examples

SELECT * FROM information_schema.COLUMNS\G
...
*************************** 9. row ***************************
           TABLE_CATALOG: def
            TABLE_SCHEMA: test
              TABLE_NAME: t2
             COLUMN_NAME: j
        ORDINAL_POSITION: 1
          COLUMN_DEFAULT: NULL
             IS_NULLABLE: YES
               DATA_TYPE: longtext
CHARACTER_MAXIMUM_LENGTH: 4294967295
  CHARACTER_OCTET_LENGTH: 4294967295
       NUMERIC_PRECISION: NULL
           NUMERIC_SCALE: NULL
      DATETIME_PRECISION: NULL
      CHARACTER_SET_NAME: utf8mb4
          COLLATION_NAME: utf8mb4_bin
             COLUMN_TYPE: longtext
              COLUMN_KEY: 
                   EXTRA: 
              PRIVILEGES: select,insert,update,references
          COLUMN_COMMENT: 
            IS_GENERATED: NEVER
   GENERATION_EXPRESSION: NULL
...

CREATE TABLE t (
  s1 VARCHAR(20) DEFAULT 'ABC',
  s2 VARCHAR(20) DEFAULT (concat('A','B')),
  s3 VARCHAR(20) DEFAULT ("concat('A','B')"),
  s4 VARCHAR(20),
  s5 VARCHAR(20) DEFAULT NULL,
  s6 VARCHAR(20) NOT NULL,
  s7 VARCHAR(20) DEFAULT 'NULL' NULL,
  s8 VARCHAR(20) DEFAULT 'NULL' NOT NULL
);

SELECT 
  table_name, 
  column_name, 
  ordinal_position, 
  column_default,
  column_default IS NULL
FROM information_schema.COLUMNS
WHERE table_schema=DATABASE()
AND TABLE_NAME='t';
+------------+-------------+------------------+-----------------------+------------------------+
| table_name | column_name | ordinal_position | column_default        | column_default IS NULL |
+------------+-------------+------------------+-----------------------+------------------------+
| t          | s1          |                1 | 'ABC'                 |                      0 |
| t          | s2          |                2 | concat('A','B')       |                      0 |
| t          | s3          |                3 | 'concat(''A'',''B'')' |                      0 |
| t          | s4          |                4 | NULL                  |                      0 |
| t          | s5          |                5 | NULL                  |                      0 |
| t          | s6          |                6 | NULL                  |                      1 |
| t          | s7          |                7 | 'NULL'                |                      0 |
| t          | s8          |                8 | 'NULL'                |                      0 |
+------------+-------------+------------------+-----------------------+------------------------+

In the results above, the two single quotes in concat(''A'',''B'') indicate an escaped single quote - see string-literals. Note that while mariadb client appears to show the same default value for columns s5 and s6, the first is a 4-character string "NULL", while the second is the SQL NULL value.

From MariaDB 11.3:

CREATE TABLE t(
     x INT,
     start_timestamp TIMESTAMP(6) GENERATED ALWAYS AS ROW START,
     end_timestamp TIMESTAMP(6) GENERATED ALWAYS AS ROW END,
     PERIOD FOR SYSTEM_TIME(start_timestamp, end_timestamp)
) WITH SYSTEM VERSIONING;

SELECT TABLE_NAME, COLUMN_NAME, ORDINAL_POSITION, 
  IS_SYSTEM_TIME_PERIOD_START, IS_SYSTEM_TIME_PERIOD_END 
  FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME='t'\G
*************************** 1. row ***************************
                 TABLE_NAME: t
                COLUMN_NAME: x
           ORDINAL_POSITION: 1
IS_SYSTEM_TIME_PERIOD_START: NO
  IS_SYSTEM_TIME_PERIOD_END: NO
*************************** 2. row ***************************
                 TABLE_NAME: t
                COLUMN_NAME: start_timestamp
           ORDINAL_POSITION: 2
IS_SYSTEM_TIME_PERIOD_START: YES
  IS_SYSTEM_TIME_PERIOD_END: NO
*************************** 3. row ***************************
                 TABLE_NAME: t
                COLUMN_NAME: end_timestamp
           ORDINAL_POSITION: 3
IS_SYSTEM_TIME_PERIOD_START: NO
  IS_SYSTEM_TIME_PERIOD_END: YES

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