1. 遍历Query语法树,获取所有的NOT IN 谓词 2. 如果这个谓词是PredicateInValueSelect( 样式`expr not in (select ...)`) 1. 判断子查询结果集的列是否可以为空 1. 不可以为空,返回 2. 可以为空,为结果集里的每个可以为空的列rc,判定在子查询的where条件里是否有 `rc is not null`谓词 1. 如果没...
MYSQL++文档里说是,SQL null is equal to nothing else. SQL null exists when every value for a particular column is legal and you need something that means "no legal value".)。 最后提一句,如果我们希望显式地往数据库中插入一个null,那么应该使用语句 insert into tbl1(id, name, time) values( ...
create a matrix table using sql query Create a matrix table using t-sql Create a new database from existing mdf file. Create a percentage from two SUM values Create a query to remove last two characters of a string Create a view and change the data types of some variables Create a writa...
UserAge int, UserDeptID int not null, UserName nvarchar(50) not null---(null:不允许为空) ---最后一列不用加逗号 ) use database MyDataBase drop table Users 5.SQL语句---Insert 插入数据 insert into Users (UserCode,UserName) values('1001','Tom') insert into Users('1002','Jerry') ①...
SQL，全称Structured Query Language，即结构化查询语句，它的主要作用是设计，创建和管理关系数据库，关系...
(SQL Server ISNULL Function overview) We can replace NULL values with a specific value using the SQL Server ISNULL Function. The syntax for the SQL ISNULL function is as follow. 我们可以使用SQL Server ISNULL函数将NULL值替换为特定值。 SQL ISNULL函数的语法如下。
insert into customer values(2, 'Mandy', null, '13910010012', '20200211'); insert into customer values(3, 'Ray', 'us', null, '20180902'); 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 通过下面的语句获取电话为空的客户是得不到的,它的结果永远为空 ...
4. JOINs ON columns with missing values There are 4 different JOINs in SQL: Inner, Outer, Left and Right. When we use JOIN in a query, it defaults to an INNER join. Luckily for me, I took the time and read a few tutorials about JOINs. But I still made a rookie mistake. ...
-- `count(*)` does not skip `NULL` values. > SELECT count(*) FROM person; count(1) --- 7 -- `NULL` values in column `age` are skipped from processing. > SELECT count(age) FROM person; count(age) --- 5 -- `count(*)` on an empty input set returns 0. This is unlike th...
unicode_ciNULLDEFAULTNULLCOMMENT'学生姓名',PRIMARYKEY(`id`)USINGBTREE)ENGINE=MyISAMAUTO_INCREMENT=9CHARACTERSET=utf8COLLATE=utf8_unicode_ciROW_FORMAT=Dynamic;---Recordsofstudent---INSERTINTO`student`VALUES(1,'202001','张三');INSERTINTO`student`VALUES(2,'202002','李四');INSERTINTO`student`VALUES...