文件名称：从一个表中移去一行-SQL语言基础
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更新时间：2024-05-15 13:25:06
SQL 基础
从一个表中移去一行 * DEPT DEPTNO DNAME LOC ------ ---------- -------- 10 ACCOUNTING NEW YORK 20 RESEARCH DALLAS 30 SALES CHICAGO 40 OPERATIONS BOSTON 50 DEVELOPMENT DETROIT 60 MIS ... “…从一个表中删去一行…” DEPT DEPTNO DNAME LOC ------ ---------- -------- 10 ACCOUNTING NEW YORK 20 RESEARCH DALLAS 30 SALES CHICAGO 40 OPERATIONS BOSTON 60 MIS ... * Removing a Row from a Table The slide graphic removes the DEVELOPMENT department from the DEPT table (assuming that there are no constraints defined on the DEPT table). Instructor Note After all the rows have been eliminated with the DELETE statement, only the data structure of the table remains. A more efficient method of emptying a table is with the TRUNCATE statement. You can use the TRUNCATE statement to quickly remove all rows from a table or cluster. Removing rows with the TRUNCATE statement is faster than removing them with the DELETE statement for the following reasons: The TRUNCATE statement is a data definition language (DDL) statement and generates no rollback information. It will be covered in a subsequent lesson. Truncating a table does not fire the DELETE triggers of the table. If the table is the parent of a referential integrity constraint, you cannot truncate the table. Disable the constraint before issuing the TRUNCATE statement.