Variables and operators for SQL

One, variable declaration format:
DECLARE @< Variable name > < variable type >[,@< variable name > < variable type >...];
Assignment: With a SELECT statement.
Example: DECLARE @varl int, @var2 money
SELECT @var1 =100, @var2 =$27.95
SELECT @var1, @var2

Second, operator
1. Arithmetic operator + 、-、 *,/,% (modulo)
2. Bitwise operator & (with), | (or), ^ (XOR), ~ (negation)
3. Comparison operators <, >, =, >=, <=, <>;
4. The string operator string operator (+) implements a concatenation operation between strings. As the result of ' abc ' + ' 123 ' is: ' abc123 '.

5. Precedence of Operators
Brackets ();
Take back operation: ~;
Multiply, divide, modulus operation: *,/,%;
Xor or operation: ^;
and operations: |;
Not connected;
and connections;
or connection.