Difference between revisions of "ALTER TABLE"
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| (<column> <datatype> [<column constraint>] [,...]) | | (<column> <datatype> [<column constraint>] [,...]) | ||
| CONSTRAINT (<column> SET <column constraint> <value> [,...]) | | CONSTRAINT (<column> SET <column constraint> <value> [,...]) | ||
| − | | | + | | <table constraint> |
| DROP [COLUMN] <column> | | DROP [COLUMN] <column> | ||
| (<column> [,...]) | | (<column> [,...]) | ||
Revision as of 14:05, 19 March 2009
Contents
ALTER TABLE
Class
SQL Applications
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, DATA TYPES, 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
