Friday, November 07, 2014

TSQLTutorial: Deleting Data

The SQL DELETE command is used to remove data from tables. To delete all the rows in a table at once,
Use this syntax:
DELETE FROM customers
Guru’s Guide to Transact-SQL
Similarly to INSERT, the FROM keyword is optional. Like UPDATE, DELETE can optionally include a WHERE
clause to qualify the rows it removes. Here's an example:
DELETE FROM customers
WHERE LastName<>'Doe'
SQL Server provides a quicker, more brute-force command for quickly emptying a table. It's similar to the
dBASE ZAP command and looks like this:
TRUNCATE TABLE customers
TRUNCATE TABLE empties a table without logging row deletions in the transaction log. It can't be used
with tables referenced by FOREIGN KEY constraints, and it invalidates the transaction log for the entire
database.
Once the transaction log has been invalidated, it can't be backed up until the next full database backup.
TRUNCATE TABLE also circumvents the triggers defined on a table, so DELETE triggers don't re, even
though, technically speaking, rows are being deleted from the table. (See Chapter4, "DDL Insights," for

more information.)

TSQL Tutorial...

No comments:

Post a Comment