Which SQL statement is used to remove all rows from a table while preserving the table structure, and is classified as a DDL command that cannot be normally rolled back in most engines?
TRUNCATE is a DDL command that deallocates data pages to rapidly remove all rows without individual tuple-level logging, keeping the empty table definition intact.
What is the key difference between DELETE and DROP statements in SQL?
DELETE is a DML statement that deletes rows conditionally or completely while maintaining schema, whereas DROP is a DDL statement that eliminates both table structure and data from the data dictionary.
Which SQL command is used to modify the definition of an existing table, such as adding a new column or constraint?
The ALTER TABLE statement is used to add, delete, or modify columns and integrity constraints in an existing table.
Which SQL command is used to modify existing column values of records within a table?
UPDATE is a DML command used to change the actual stored data values within rows of an existing relation.
Which clause is used in SQL to filter rows before any grouping is performed?
The WHERE clause filters individual records prior to aggregation, whereas the HAVING clause filters groups formed by the GROUP BY clause.