1.drop語句。可以用來刪除數據庫和表。
A用drop語句來刪除數據庫：
mysql>?drop?database?hello;Query?OK,?0?rows?affected?(0.19?sec) mysql>?show?databases; +--------------------+ |?Database???????????| +--------------------+ |?information_schema?| |?mysql??????????????| |?performance_schema?| |?sys????????????????| |?test???????????????| |?trains?????????????| +--------------------+ 6?rows?in?set?(0.00?sec)
B用drop語句來刪除表：
mysql>?drop?table?q1;Query?OK,?0?rows?affected?(0.39?sec) mysql>?show?tables; +------------------+ |?Tables_in_trains?| +------------------+ |?4inall???????????| |?ava??????????????| |?book?????????????| |?c1score??????????| |?c2score??????????| |?course???????????| |?joke?????????????| |?sc???????????????| |?sc1??????????????| |?student??????????| |?student1?????????| |?teacher??????????| +------------------+ 12?rows?in?set?(0.00?sec)
2.delete語句。用來刪除表中的字段：
A通過where子句來指定刪除表中的某個記錄：
mysql>?delete?from?joke?where?gid=1; mysql>?select?*?from?joke; +------+-----------+-------+------+ |?gid??|?name??????|?sex???|?age??| +------+-----------+-------+------+ |????3?|?xiaowan2??|?male??|???22?| |????3?|?xiaowan2??|?male??|???22?| |????3?|?xiaowan2??|?male??|???22?| |????3?|?xiaowan22?|?1male?|???22?| |????0?|?joker?????|?NULL??|?NULL?| |????0?|?joker?????|?NULL??|?NULL?| +------+-----------+-------+------+ 6?rows?in?set?(0.00?sec)
注意：如果delete語句中沒有加入where就會把表中的所有記錄全部刪除：
mysql>?select?*?from?student1; +------+--------+------+------+ |?s????|?sname??|?sage?|?ssex?| +------+--------+------+------+ |????1?|?劉一???|???18?|?男???| |????2?|?錢二???|???19?|?女???| |????3?|?張三???|???17?|?男???| |????4?|?李四???|???18?|?女???| |????5?|?王五???|???17?|?男???| |????6?|?趙六???|???19?|?女???| +------+--------+------+------+ 6?rows?in?set?(0.00?sec) mysql>?delete?from?student1;Query?OK,?6?rows?affected?(0.19?sec) mysql>?select?*?from?student1;Empty?set?(0.00?sec)
B通過select子句來刪除表中的某個記錄：
mysql>?delete?from?student1?where?s?in?(select?s?from?student?where?sage=18?and?ssex="男");Query?OK,?1?row?affected?(0.13?sec) mysql>?select?*?from?student1; +------+--------+------+------+ |?s????|?sname??|?sage?|?ssex?| +------+--------+------+------+ |????2?|?錢二???|???19?|?女???| |????3?|?張三???|???17?|?男???| |????4?|?李四???|???18?|?女???| |????5?|?王五???|???17?|?男???| |????6?|?趙六???|???19?|?女???| +------+--------+------+------+ 5?rows?in?set?(0.00?sec)
3.用truncate來刪除表中的所以字段：
mysql>?select?*?from?student1; +------+--------+------+------+ |?s????|?sname??|?sage?|?ssex?| +------+--------+------+------+ |????1?|?劉一???|???18?|?男???| |????2?|?錢二???|???19?|?女???| |????3?|?張三???|???17?|?男???| |????4?|?李四???|???18?|?女???| |????5?|?王五???|???17?|?男???| |????6?|?趙六???|???19?|?女???| +------+--------+------+------+ 6?rows?in?set?(0.00?sec) mysql>?truncate?table?student1;Query?OK,?0?rows?affected?(0.28?sec) mysql>?select?*?from?student1;Empty?set?(0.00?sec)
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