1、N个以上条件的查询
在项目中经常会遇到对一个表或视图进行多个条件查询,如下:
SELECT * FROM tab1 WHERE col1>v1 AND col2>v2 AND col3>v3 AND col4>v4 ....
记得刚开始参加工作时是直接在代码里封装这多达好几十个条件的SQL语句,后来改为在存储过程中用 IF 语句判断,最近又遇到此类问题,参考网上几位牛人的方法,改用OR直接查询,代码减少不说,也方便维护
CREATE TABLE history ( code VARCHAR(6), [name] nvarchar(20), price money, datadt datetime ) create proc proc_getCodes( @dt datetime, @price money ) as select * from history where (@datadt IS NULL or datadt>@dt) and (@price IS NULL or price>@price) )
/*查询表的总行数,
SELECT dbo.row_count('tradeDetail')
*/
ALTER FUNCTION row_count(@tableName SYSNAME) RETURNS BIGINT AS BEGIN DECLARE @nn BIGINT IF @tableName IS NOT NULL BEGIN SELECT @nn=SUM(rows) FROM sys.partitions WHERE index_id IN(0,1) AND [object_id]=OBJECT_ID(@tableName) END RETURN @nn END GO
查询tradeStat表的所有列名
select name from syscolumns where id in (select id from sysobjects where type = 'u' and name = 'tradeStat') --或者 SELECT name FROM syscolumns WHERE id=OBJECT_ID('tradeStat')
更改表的字段类型
alter table tradeDetail alter column price smallMoney
待续。。。