SQL Server-Basic

Data type

• Character type

varchar (8000): Supports up to 8,000 characters

nvarchar (4000): Supports up to 4,000 characters

• Integral type

• Floating point Type

Operators, functions

ISNULL (value,0);  --if NULL, the return value is 0sum (column); --Add this column value IsNumeric ("123")--non-numeric return 0, number returned 1

modifying fields

ALTER TABLE tname DROP COLUMN cname;  --delete field alter TABLE tname ADD CNAME VARCHAR (100);  --Add the field alter TABLE tname add DEFAULT (' no ') for the CNAME with VALUES; --Modify the field default value

SELECT statement

Go heavy

SELECT DISTINCT cname from tname WHERE ...;

Result set Query

SELECT * from Tname WHERE the CNAME in (' V1 ', ' v2 ');

If the result set is empty

SELECT * from Tname WHERE cname in ('); --cannot be written as in (), so there is a syntax error.

External connection

Outer joins are divided into three kinds: Left outer connection, right outer connection, full outer connection

This article is from the "Zero Technology Road" blog, please be sure to keep this source http://zerohou.blog.51cto.com/3019528/1615326

SQL Server-Basic