补充,今天发现一种方法也可以实现和Exists一样的效果,而且好像这种写法比not exists要快一点,具体的可以自行对比一下。 例如:查询在商品审核表goods_check已经通过(state=1)的商品,但是在goods表不存在的数据(两个表通过g_id关联); 1、exists写法: selectcount(*)fromgoods_check kwherek.state=1andnotexists(s...
SELECT TABLE_NAME FROM DBName.INFORMATION_SCHEMA.Tables WHERE TABLE_NAME='Article' How do I check this in C#?As for how you check that in C#? You just make sure the Row count returned from the query is 1. See this article I have already posted. How do I get the number of rows ...
alter table 表名 add constraint 约束名 check(约束规则),constraint 约束名 check(约束规则); go 示例: -- 添加一个默认约束 use testss; go if exists(select * from sysobjects where name='check1') alter table test1 drop constraint check1; go alter table test1 add constraint check1 check(height...
it returns theobject ID; otherwise, it returnsNULL. We can use theCOALESCE()function to convert this result into a boolean value. However,this approach returnstrueif any database object with that name exists in the schema, not just a table. ...
CHECK (expr) 1. 在MySQL 8.0.16,CREATE TABLE添加了针对所有存储引擎的表和列的CHECK约束的核心特性。CREATE TABLE允许如下针对表或列的约束语法: [CONSTRAINT [symbol]] CHECK (expr) [[NOT] ENFORCED] 1. 可选的symbol指定了约束的名称,如果省略,MySQL会自动生成一个类似:${table_name}_check_${seq_num...
exists: 强调的是是否有返回集,不需知道具体返回的是什么,只要exists引导的子句有结果集返回,这个条件就算成立。 外层查询一条 -》 判断子查询是否有返回 -》 有返回则为true -》 外层该条记录可显示 -》 继续外层遍历下一条 exists 和in 的区别
INSERT INTO CHECK2_T1 VALUES(10002,'C1') CREATE TABLE CHECK3_T1 ( ID INT, C1 CHAR(7000) ) CREATE TABLE CHECK3_T2 ( ID INT, C1 CHAR(7000) ) DECLARE @I INT SET @I=1 WHILE @I<=20000 BEGIN IF @I%2 =0 BEGIN INSERT INTO CHECK3_T1 SELECT @I,'C1' ...
CREATE TABLE- 创建新表 ALTER TABLE- 变更(改变)数据库表 DROP TABLE- 删除表 CREATE INDEX- 创建索引(搜索键) DROP INDEX- 删除索引 2、SQL基础语法 (1)SELECT 语句 SELECT 语句用于从数据库中选取数据。 SELECTcolumn_name,column_nameFROMtable_name;SELECT*FROMtable_name; ...
exists(select * from Sysobjects where name = 'stuInfo')drop table stuInfogocreate table stuInfo...
SELECT o_orderpriority, COUNT(*) AS Order_Count FROM orders WHERE o_orderdate >= '2000/04/01' AND o_orderdate < DATEADD (mm, 3, '2000/04/01') AND EXISTS ( SELECT * FROM lineitem WHERE l_orderkey = o_orderkey AND l_commitdate < l_receiptdate ) GROUP BY o_orderpriority ORDER...