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SQL中的DDL,DML,DCL語言

2019-11-03 08:35:00
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   感覺自己是比較笨的,學(xué)習(xí)過SQL語言,但是卻分不太清楚DDL、DML、DCL語言,所以呢,今天就厚著臉皮問了老師,現(xiàn)在就自己目前的了解來總結(jié)一下。

1、DDL(DATA DEFINITION LANGUAGE)數(shù)據(jù)描述語言

     DDL語句不會(huì)產(chǎn)生還原數(shù)據(jù),所以刪除的數(shù)據(jù)也是無法恢復(fù)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)數(shù)據(jù)操縱魚語言


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)數(shù)據(jù)控制語言


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
感覺是要好那么一點(diǎn)了,至少不那么糊涂了,畢竟自己也學(xué)了那么久,不能什么都不知道三,不能只曉得就一個(gè)create、update、drop,嘿嘿!!! 
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