DELETE - SQL Command
Marks records for deletion.
DELETE FROM [DatabaseName!]TableName [WHERE FilterCondition1 [AND | OR FilterCondition2 ...]]
- FROM [DatabaseName!]TableName
- Specifies the table in which records are marked for deletion.
DatabaseName! specifies the name of a non-current database containing the table. You must include the name of a database containing the table if the database is not the current database. Include the exclamation point (!) delimiter after the database name and before the table name.
- WHERE FilterCondition1 [AND | OR FilterCondition2 ...]
- Specifies that Visual FoxPro marks only certain records for deletion.
FilterCondition specifies the criteria that records must meet to be marked for deletion. You can include as many filter conditions as you like, connecting them with the AND or OR operator. You can also use the NOT operator to reverse the value of a logical expression, or use EMPTY( ) to check for an empty field.
Records marked for deletion aren't physically removed from the table until PACK is issued. Records marked for deletion can be recalled (unmarked) with RECALL.
If SET DELETED is set to ON, records marked for deletion are ignored by all commands that include a scope.
Unlike DELETE, DELETE - SQL uses record locking when marking multiple records for deletion in tables opened for shared access. This reduces record contention in multiuser situations, but may reduce performance. For maximum performance, open the table for exclusive use or use FLOCK( ) to lock the table.
The following example opens the
customer table in the
testdata database. DELETE - SQL is used to mark all records for deletion where the
country field contains USA. All the records marked for deletion are displayed. RECALL ALL is used to unmark all the records marked for deletion.
CLOSE DATABASES CLEAR OPEN DATABASE HOME(2)+"Data\testdata" USE customer && Open Customer table DELETE FROM customer WHERE country = "USA" && Mark for deletion CLEAR LIST FIELDS company, country FOR DELETED( ) && List marked records * If the file were packed at this point the records would be deleted WAIT WINDOW "Records currently marked for deletion"+CHR(13) + ; "Press any key to revert..." * Unmark all records marked for deletion RECALL ALL CLEAR * Verify reverted records COUNT FOR DELETED( )=.T. TO nDeleted * Convert nDeleted to a character string and display information WAIT WINDOW ALLTRIM(STR(nDeleted)) + " records marked for deletion."