查看索引
SHOW INDEX FROM student;
创建索引
1.PRIMARYKEY(主键索引)
ALTER TABLE table_name ADD PRIMARYKEY (column);
2.UNIQUE(唯一索引)
ALTER TABLE table_name ADD UNIQUE (column );
3.INDEX(普通索引)
ALTER TABLE table_name ADD INDEX index_name (column);
4.FULLTEXT(全文索引)
ALTER TABLE table_name ADD FULLTEXT ( column );
5.多列索引(组合索引)
ALTER TABLE table_name ADD INDEX index_name (column1,column2,column3);
查看SQL执行计划
EXPLAIN SELECT sno,sname,sage FROM student;
查看表字段及字段类型
DESCRIBE student;
修改表字段类型及长度
ALTER TABLE student MODIFY COLUMN stu_name VARCHAR(20);
修改表字段默认值 若存在默认值先删除后修改
ALTER TABLE table_name ALTER COLUMN column_name DROP DEFAULT;
ALTER TABLE table_name ALTER COLUMN column_name SET DEFAULT '哈哈';