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 mysqlshow.

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';

From MariaDB 10.2.7:

+------------+-------------+------------------+-----------------------+------------------------+
| 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 mysql-command-line-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.

MariaDB 10.2.6 and before:

+------------+-------------+------------------+-----------------+------------------------+
| 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            |                      1 |
| t          | s5          |                5 | NULL            |                      1 |
| t          | s6          |                6 | NULL            |                      1 |
| t          | s7          |                7 | NULL            |                      0 |
| t          | s8          |                8 | NULL            |                      0 |
+------------+-------------+------------------+-----------------+------------------------+