MySQL float类型查询
字段 ID float(7,4)
当ID=3.0000时我可以select * from table where ID=3或者select * from table where ID=3.0000查出来
而当ID=3.1000时用select * from table where ID=3.1 或者select * from table where ID=3.1000都查不出来
此时解决方法有2种:
1.将float改为double类型,不会出现这种问题.但是如果数据库中数据量庞大,或者修改量太大,则不适合这个方法.这个方法只适合设计数据库的初期阶段.
2.设置float的精度然后进行查询就可以了.
select * from table where format(ID,4) =format(3.1000,4)
MySQL 的 RowNum 实现
MySQL 下面没有RowNum,排序后序号却无法得到,比较麻烦!
在网上找了再三,通过比较,确认了以下的方法是可行的 :
SELECT @rownum:=@rownum+1 rownum, CollectSn From (SELECT @rownum:=0,bbgmain.* FROM qbdb.bbgmain WHERE collectsn!='' ORDER BY collectsn limit 10) t
- table comments:
- create
CREATE TABLE `table1` (
`field1` VARCHAR(20) COLLATE utf8_general_ci NOT NULL DEFAULT '',
`field2` INTEGER(11) DEFAULT NULL COMMENT 'aaa',
PRIMARY KEY (`field1`)
)ENGINE=InnoDB
CHARACTER SET 'utf8' COLLATE 'utf8_general_ci'
COMMENT='AAAA;
- query
SHOW CREATE TABLE table1;
select * from information_schema.tables where table_name='TABLE1';
- modify
ALTER TABLE table1 COMMENT = 'new comment';
- table field comments:
- create
CREATE TABLE `table1` (
`field1` VARCHAR(20) COLLATE utf8_general_ci NOT NULL DEFAULT '',
`field2` INTEGER(11) DEFAULT NULL COMMENT 'aaa',
PRIMARY KEY (`field1`)
)ENGINE=InnoDB
CHARACTER SET 'utf8' COLLATE 'utf8_general_ci'
COMMENT='AAAA;
- query
show full fields from tableA;
select column_name, column_comment from information_schema.columns where table_name='table1';
- modify
ALTER TABLE table1 MODIFY COLUMN field1 varchar(20) not null COMMENT 'field new Commonts';