ALTER TABLE

Purpose

Used to add, modify or delete table columns and constraints

Syntax

ALTER [IGNORE] TABLE [<database>!]<table>

ADD [COLUMN] (<column> <datatype> [<column constraints>] [,...]) | <table constraint>

| ALTER | MODIFY [COLUMN] <column> [SET DEFAULT <value> | DROP DEFAULT] | (<column> <datatype> [<column constraint>] [,...])

| CONSTRAINT (<column> SET <column constraint> <value> [,...]) | <table constraint>

| DROP [COLUMN] <column> | (<column> [,...]) | CONSTRAINT (<column> <column constraint> [,...]) | <table constraint>

| SET CHECK <condition> [ERROR <message>]

| RENAME (<column>,<new column>)

See Also

ADD TABLE, ALTER INDEX, CONSTRAINTS, CREATE TABLE, CREATE TRIGGER, DATA TYPES, DELETE TRIGGER, GETENV(), INSERT, SELECT, SET TCACHE

Description

The ALTER TABLE command is used to add, modify or delete table columns and constraints and to rename columns. The ALTER TABLE statement automatically reloads the original data of the table back into the original columns. You must have ALTER privilege on the table. The table will be locked for EXCLUSIVE use during the operation.

Keywords	Description
IGNORE	If IGNORE is omitted and there are duplicate UNIQUE keys in the table, the ALTER TABLE is aborted with an error. If IGNORE is specified, records containing a duplicate UNIQUE key are deleted, leaving only the first row with that key.
database	The name of the database to which the table to be altered belongs. Databases in Recital are implemented as directories containing files that correspond to the tables and associated files in the database. Operating System file protection can be applied individually to the files for added security. The directory is a sub-directory of the Recital data directory. The environment variable / symbol DB_DATADIR points to the current Recital data directory and can be queried using the GETENV() function. Files from other directories can be added to the database using the ADD TABLE command or via the database catalog and SET AUTOCATALOG functionality. The '!' character must be included between the database name and the table name.
table	The name of the table to be altered.
ADD	This will insert one or more new columns into the table
COLUMN	Optional COLUMN keyword.
column	The name of the column to operate on.
datatype	The data type to be stored in the column, and the applicable length or precision.
column constraint	The column constraint.
table constraint	The table constraint.
MODIFY	These are used to change existing column definitions and column and table constraints.
SET DEFAULT <expr>	Specify the DEFAULT column constraint to set a default value for the specified column. The <expr> must evaluate to the same data type as the target column. The column's value can subsequently be updated.
DROP DEFAULT	Remove the DEFAULT column constraint for the specified column.
DROP	This is used to delete existing column definitions and column and table constraints.
CONSTRAINT	This keyword is used if the constraint refers to a column.
SET	Precedes an existing column constraint whose value is being changed.
value	The new value for the specified column constraint.
SET CHECK <condition>	Specify CHECK table constraint. This validation is activated when an operation to insert, update or delete records in the table is called. The <condition> specified must evaluate to True (.T.) for the operation to succeed. If the <condition> evaluates to False (.F.) the operation is abandoned and the ERROR table constraint message is displayed. If the ERROR table constraint has not been defined, a default error message is displayed.
ERROR <message>	Specify ERROR table constraint. The <message> is the error message to be displayed if the CHECK table constraint evaluates to False (.F.).
RENAME	This is used to change the name of an existing column.
new column	The new name for the column.

Example

// Add new column with column constraints
EXEC SQL
ALTER TABLE customer ADD COLUMN timeref char(8)
  CHECK validtime(timeref)
  ERROR "Not a valid time string";
 
// Alter existing columns to add column constraints
EXEC SQL
ALTER TABLE customer
  ALTER COLUMN available CALCULATED limit-balance
  ALTER COLUMN limit RECALCULATE
  ALTER COLUMN balance RECALCULATE;
 
//or
EXEC SQL
ALTER TABLE customer
  ALTER (available CALCULATED limit-balance,
  limit RECALCULATE,
  balance RECALCULATE);
 
// Add new column, add column constraint,
// modify column datatype and drop constraints then drop column
EXEC SQL
ALTER TABLE customer ADD (timeref char(8));
 
EXEC SQL
ALTER TABLE customer
  ALTER CONSTRAINT
  (timeref SET CHECK validtime(timeref)
  ERROR "Not a valid time string");
 
EXEC SQL
ALTER TABLE customer
  ALTER (timeref datetime)
  DROP CONSTRAINT (timeref CHECK, timeref ERROR);
 
EXEC SQL
ALTER TABLE customer DROP (timeref);
 
// Add an ONUPDATE table constraint 
EXEC SQL
ALTER TABLE customer
  MODIFY ONUPDATE "do check_update";
 
// Add and then remove CHECK table constraint
EXEC SQL
ALTER TABLE customer SET CHECK checkit() error "Invalid operation";
 
set sql off
use customer
display dictionary
edit  && Save and Exit will call validation
use
 
EXEC SQL 
ALTER TABLE customer DROP CHECK;
 
// Rename column
EXEC SQL
ALTER TABLE customer RENAME(first_name,forename);

Products

Recital Database Server, Recital Mirage Server, Recital Terminal Developer