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Deleting all rows from a table can be very time-consuming. Some DBMS [clarification needed] offer a TRUNCATE TABLE command that works a lot quicker, as it only alters metadata and typically does not spend time enforcing constraints or firing triggers. DELETE only deletes the rows. For deleting a table entirely the DROP command can be used.
In SQL, the TRUNCATE TABLE statement is a data manipulation language (DML) [1] operation that deletes all rows of a table without causing a triggered action. The result of this operation quickly removes all data from a table , typically bypassing a number of integrity enforcing mechanisms.
In the code shown, the virtual tables are called DELETED and INSERTED. On a specific RDBMS they could have different names. Another RDBMS (Db2) even let the name of these logical tables be specified. In the code shown, comments are in C/C++ style, they could not be supported by a specific RDBMS, or a different syntax should be used.
Row-level trigger: This gets executed before or after any column value of a row changes. Column-level trigger: This gets executed before or after the specified column changes. For each row type: This trigger gets executed once for each row of the result set affected by an insert/update/delete.
The SQL SELECT statement returns a result set of rows, from one or more tables. [1] [2] A SELECT statement retrieves zero or more rows from one or more database tables or database views. In most applications, SELECT is the most commonly used data manipulation language (DML) command.
In computer programming, create, read, update, and delete (CRUD) are the four basic operations (actions) of persistent storage. [1] CRUD is also sometimes used to describe user interface conventions that facilitate viewing, searching, and changing information using computer-based forms and reports .
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With them we can easily allow or deny some actions for users on the tables or records (row level security). DCL commands are: [2] GRANT gives specified permissions for the table (and other objects) to, or assigns a specified role with certain permissions to, specified groups or users of a database; REVOKE