SQL中的DDL,DML,DCL语言
感觉自己是比较笨的,学习过SQL语言,但是却分不太清楚DDL、DML、DCL语言,所以呢,今天就厚着脸皮问了老师,现在就自己目前的了解来总结一下。
1、DDL(DATA DEFINITION LANGUAGE)数据描述语言
DDL语句不会产生还原数据,所以删除的数据也是无法恢复的
CREATE - to create objects in the database
ALTER - alters the structure of the database
DROP - delete objects from the database
TRUNCATE - remove all records from a table, including all spaces allocated for the records are removed
COMMENT - add comments to the data dictionary
GRANT - gives user's access privileges to database
REVOKE - withdraw access privileges given with the GRANT command
2、DML(DATA MANIPULATION LANGUAGE)数据操纵鱼语言
SELECT - retrieve data from the a database
INSERT - insert data into a table
UPDATE - updates existing data within a table
DELETE - deletes all records from a table, the space for the records remain
CALL - call a PL/SQL or Java subprogram
EXPLAIN PLAN - explain access path to data
LOCK TABLE - control concurrency
3、DCL(DATA CONTROL LANGUAGE)数据控制语言
COMMIT - save work done
SAVEPOINT - identify a point in a transaction to which you can later roll back
ROLLBACK - restore database to original since the last COMMIT
SET TRANSACTION - Change transaction options like what rollback segment to use
感觉是要好那么一点了,至少不那么糊涂了,毕竟自己也学了那么久,不能什么都不知道三,不能只晓得就一个create、update、drop,嘿嘿!!!
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