Variables & Operators in MySQL


In this tutorial, I am going to explain about MySQL variables and operators with examples. Without wasting time, let’s start.


A variable is a characteristic notation with a character value. This value may be changed over time.  Variables in MySQL are represented by the @ symbol.
Example 1:
  1. Set @name = 'Hello! Vatsa';  
  2. SELECT @name
Example 2:
  1. SET @a = "20/10/2000";  
  2. SET @b = "20/10/2020";  
  3. SET @sql = CONCAT('SELECT * FROM <table_name> WHERE date IN (', @a, ',', @b, ')' );  
  4. SELECT @sql; 


Operators may be used to build expressions. MySQL operators are very similar to mathematical operators.  
There are two kinds of operators.
  1. Binary
  2. Unary
Binary operators work with two operands, but unary work with one.
  • An operator may have one or two operands.
  • An operand is one of the inputs (arguments) of an operator.
There are different types of operators in MySQL, let’s discuss them one by one.
  • Arithmetic operators
  • Boolean operators
  • Relational operators
  • Bitwise operators
  • Other operators
  • Unary operators


In MySQL, a unary operator is an operator that works on single operand.
Syntax: operator operand.
  1. SELECT +5, 9;  
  2. SELECT -(4-54); 
The ‘-‘ unary operator changes the positive values to negative and vice versa.
  1. SELECT NOT (4>8); 
The NOT operator negates a value. The result of the 4>8 comparison is false and the negation operator negates it to true.


These are some arithmetic operators in mysql, let’s discuss them one by one.
  1. Multiplication
  2. Division
  3. Integer
  4. Division
  5. Addition
  6. Subtraction modulo
1)   Addition and subtraction operators.
  1. SELECT 4 + 7 - 1; 
2) These are multiplication and division operators that we know from mathematics.
  1. SELECT 4*3/6; 
3) The below SQL statement shows the difference between the division and integer division operators. The first returns a floating point number, the second returns an integer.
  1. SELECT 7/3, 7 DIV 3; 
4) The % operator is called the modulo operator. It finds the remainder of division of one number by another. 11 % 3, 11 modulo 3 is 2, because 3 goes into 11 three times with a remainder of 2.
  1. SELECT 15 % 43; 


MySQL understands these logical operators:
  1. AND
  2. OR 
  3. NOT
  4. XOR
Logical operators return TRUE or FALSE. In MySQL, 1 is true, 0 is false.
Example 1: AND Operator
The AND operator evaluates to true, if both operands are true.
  2. FALSE AND TRUE,    
  3. TRUE AND FALSE,    
  4. TRUE AND TRUE;   
The first three operations evaluate to false, the last one to true.
  1. SELECT 5=5 AND 6=6; 
Both operands are true, so the result is true (1).
Example 2: OR Operator
The OR operator evaluates to true, if at least one of the operands is true.
  2. FALSE OR TRUE,    
  3. TRUE OR FALSE,    
  4. TRUE OR TRUE;  
The first operation evaluates to false, and other operations evaluate to true.
The XOR operator evaluates to true, if exactly one of the operands is true.
Two of the operations result in true.
The NOT operator is negation operator. It makes true false and false true.
  2. SELECT NOT (3=3); 


Relational operators are used to compare values. Usage of the relational operators is known from mathematics. These operators always result in Boolean value.
For Example:
  1. SELECT 3*3=9, 9=9; 
The = is the equality operator.
  1. SELECT 3 < 4, 3 <> 5, 4 <= 4, 5 != 5; 


In the Bitwise operators, Decimal numbers are natural to humans. Binary numbers are native to computers. Binary, octal, decimal or hexadecimal symbols are only notations of the same number. These operators work with bits of a binary number. We have binary logical operators and shift operators.
A)  The bitwise AND operator performs bit-by-bit comparison between two numbers. The result for a bit position is 1 only if both corresponding bits in the operands are 1.
For example:
  1. SELECT 6 & 3, 3 & 6; 
& 00011
=  00010
The first number is a binary notation of 6. The second is 3. The result is 2 (00010).
B)  The bitwise OR operator performs bit-by-bit comparison between two numbers. The result for a bit position is 1 if either of the corresponding bits in the operands is 1.
For example:
  1. SELECT 7 | 3, 3 | 7; 
  |  00011
  =  00111
The result is 00111 or decimal 7.
C) The bitwise shift operators shift bits to the right or left.
  • number << n : multiply number 2 to the nth power 
  • number >> n : divide number by 2 to the nth power
For example 1:
  1. SELECT 6 >> 1; 
These operators are also called arithmetic shift.
>>  00001
We shift each of the bits of the number six to the right. It is equal to dividing the six by 2. The result is 00011 or decimal 3.
For example 2:
  1. SELECT 6 << 1; 
    << 00001
     =  01100
We shift each of the bits of the number six to the left. It is equal to multiplying the number six by 2. The result is 01100 or decimal 12.


There are some other operators left. These include IS, IN, LIKE, REGEXP, BETWEEN.
The IS operator tests if an operand is a Boolean value.
For example:
  1. SET @vatsa = TRUE;  
  2. SELECT @vatsa IS TRUE
We set a variable to Boolean false. We check if the variable is FALSE using the IS operator.
We can use the IN operator in two cases.
  1. SELECT 'Ram' IN ('Ram''Hari''Mohan',’vatsa’); 
Here we check, if the string value 'Ra,' is in the list of names, following the IN operator. The return is a boolean value.


The operator precedence tells us which operators are evaluated first. The precedence level is necessary to avoid ambiguity in expressions.
For example:
  1. Select 4 + 5 * 5; 
Like in mathematics, the multiplication operator has a higher precedence than addition operator. So the outcome is 29.
  1. SELECT (3 + 8) * 5, ((1+2)*3)*5-(8+(1*5)); 
To change the order of evaluation, we can use square brackets. Expressions inside square brackets are always evaluated first.
The first expression evaluates to 28, because the multiplication operator has a higher precedence, than the addition one. In the second example, we have used square brackets to change the order of precedence. So the second expressions evaluates to 55, and third expression evaluates to 32 according to BODMAS rule.


Sometimes the precedence is not satisfactory to determine the outcome of an expression. There is another rule called associativity. The associativity of operators determines the order of evaluation of operators with the same precedence level.
  1. SELECT 9 / 3 * 3; 
What is the outcome of this expression? 9 or 1? The multiplication, deletion and the modulo operator are left to right associated. So the expression is evaluated this way: (9 / 3) * 3 and the result is 9.
  1. SELECT 9 / 3 * 3; 
The associativity rule is left to right.
  1. SELECT 0 AND 0 OR 1; 
The associativity rule is again left to right. If it was right to left, the result would be 0. Arithmetic, boolean, relational and bitwise operators are all left to right associated.


In this article, I have discussed the concept MySQL variables and operators with various examples.
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