ALTER

ALERT can be used to modify any table settings or data within the table:

Syntax

sql

ALTER TABLE [db.]table
   [ADD COLUMN name type [options]
    | DROP COLUMN name
    | RENAME name
   ]

ALTER TABLE [db.]table
   [ADD COLUMN name type [options]
    | DROP COLUMN name
    | RENAME name
   ]

Adds a new column to the table:

sql

ALTER TABLE monitor ADD COLUMN load_15 double;

ALTER TABLE monitor ADD COLUMN load_15 double;

Definition of column is the same as in CREATE.

We can set the new column's location. In first position for example:

sql

ALTER TABLE monitor ADD COLUMN load_15 double FIRST;

ALTER TABLE monitor ADD COLUMN load_15 double FIRST;

After an existing column:

sql

ALTER TABLE monitor ADD COLUMN load_15 double AFTER memory;

ALTER TABLE monitor ADD COLUMN load_15 double AFTER memory;

Adds a new column as a tag(primary key) with a default value:

sql

ALTER TABLE monitor ADD COLUMN app STRING DEFAULT 'shop' PRIMARY KEY;

ALTER TABLE monitor ADD COLUMN app STRING DEFAULT 'shop' PRIMARY KEY;

Removes a column from the table:

sql

ALTER TABLE monitor DROP COLUMN load_15;

ALTER TABLE monitor DROP COLUMN load_15;

The removed column can't be retrieved immediately by all subsequent queries.

Renames the table:

sql

ALTER TABLE monitor RENAME monitor_new;

ALTER TABLE monitor RENAME monitor_new;

This command only renames the table; it doesn't modify the data within the table.