Information Schema COLUMNS Table

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

It contains the following columns:

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