Operators in MySQL

Arithmetic operator

Arithmetic operator , Include +、-、*、/ perhaps DIV、% perhaps MOD（ Remainder or modulus ）.

• MySQL in ,+ Just add the numbers , If a non numeric type is encountered ,MySQL Will first try to convert it to a number , If the conversion fails , It is regarded as a numerical value 0 Handle . in other words , There is Implicit conversion .
• MySQL in , String splicing uses functions CONCAT(str1,str2,...) Realization .
• Null values participate in the operation , The result of the operation is still null .
• MySQL in , Divisor is 0 when , The result is null , namely NULL.

+ Just add the numbers

# MySQL in ,+ Just add the numbers , If a non numeric type is encountered ,MySQL Will first try to convert it to a number , If the conversion fails , It is regarded as a numerical value 0 Handle . in other words , There is   Implicit conversion .
SELECT 100 + '2'
FROM DUAL; --  return 102

SELECT 100 + 'A'
FROM DUAL; --  return 100

SELECT 'A' + 'B'
FROM DUAL; --  return 0

String splicing function CONCAT()

# MySQL in , String splicing uses functions CONCAT() Realization 
SELECT CONCAT('HEL','LO')
FROM DUAL; --  return HELLO

SELECT CONCAT('a','b','c')
FROM DUAL; --  return abc

Null values participate in the operation , The result is still null

SELECT 100 + NULL
FROM DUAL; --  return NULL

Divisor is 0 when , The result is empty.

SELECT 100/0
FROM DUAL; --  return NULL

Comparison operator

Comparison operator , Include =、<=>、<> perhaps !=、<、<=、>、>=,
Also include IS NULL、IS NOT NULL、ISNULL()、LEAST()、GREATEST()、BETWEEN AND、IN()、NOT IN()、LIKE、REGEXP、RLIKE.

• =, The equal sign operator . If one side is numerical , The other side is non numeric , Then there is implicit conversion . namely , First try to convert non numeric values to numeric values , If the conversion fails , It is regarded as a numerical value 0 Handle .
• =, The equal sign operator . If both sides are strings , Compare the characters in the string ANSI code .
• =, The equal sign operator , If either side appears NULL, The result of the comparison is NULL.
• <=>, Security equals operator . and = similar , The difference lies in ,<=> It can be done to NULL Judge .
• The judgment field is NULL： Field <=>NULL、 Field IS NULL、ISNULL( Field ).
• The judgment field is not NULL：NOT Field <=>NULL、 Field IS NOT NULL、NOT ISNULL( Field ).
• BETWEEN Conditional lower bound AND Conditional upper bound , Including boundaries .
• Use LIKE Fuzzy query , among ,
  • %, A character representing an indefinite number . Can represent 0 Characters , Can represent 1 Characters , It can also represent multiple characters .
  • _, Represents any character .
  • \, Escape character .ESCAPE character , Specify a character as an escape character .
• REGEXP, Regular matching . Common wildcards are as follows ,
  • ^, Match the beginning .
  • $, Match the end .
  • ., Matches any character .
  • *, matching 0 One or more characters in front of it . such as ,x*, Match any number of x character ;[0-9]*, Match any number of numbers ;*, Match any number of any characters .
  • [], Match any character in brackets . such as ,[abc], matching a or b or c;[a-zA-Z], Match any uppercase and lowercase letters ;[0-9], Match any number .

= and <=>

#  If one side is numerical , The other side is non numeric , Then there is implicit conversion . namely , First try to convert non numeric values to numeric values , If the conversion fails , It is regarded as a numerical value 0 Handle .
SELECT 1='1',1='a',0='a','1'=1,'a'=1,'a'=0
FROM DUAL;
--  return  1 0 1 1 0 1

#  If = On both sides are strings , Compare the characters in the string ANSI code 
SELECT 'a'='a','ab'='ab','a'='b'
FROM DUAL; 
--  return  1 1 0

# =, The equal sign operator , Either side appears NULL, The results for NULL
SELECT 1=NULL,NULL='a',NULL=NULL
FROM DUAL;
--  return  NULL NULL NULL

# <=>, Security equals operator , and =（ The equal sign operator ） similar 
SELECT 1<=>'1',1<=>'a',0<=>'a','1'<=>1,'a'<=>1,'a'<=>0
FROM DUAL;
--  return  1 0 1 1 0 1

SELECT 'a'<=>'a','ab'<=>'ab','a'<=>'b'
FROM DUAL; 
--  return  1 1 0

# <=>, Security equals operator , It can be done to NULL Judge 
SELECT 1<=>NULL,NULL<=>'a',NULL<=>NULL
FROM DUAL;
--  return  0 0 1

SELECT *
FROM employees
WHERE commission_pct <=> NULL;
--  return  72  rows 

IS NULL、IS NOT NULL and ISNULL()

#  Query table employees in ,commission_pct by NULL The data of 
SELECT *
FROM employees
WHERE commission_pct <=> NULL;

SELECT *
FROM employees
WHERE commission_pct IS NULL;

SELECT *
FROM employees
WHERE ISNULL(commission_pct);

#  Query table employees in ,commission_pct Not for NULL The data of 
SELECT *
FROM employees
WHERE NOT commission_pct <=> NULL;

SELECT *
FROM employees
WHERE commission_pct IS NOT NULL;

SELECT *
FROM employees
WHERE NOT ISNULL(commission_pct);

BETWEEN … AND …

#  Check salary at [6000,8000] Employee information within the scope 
SELECT *
FROM employees
WHERE salary BETWEEN 6000 AND 8000;

SELECT *
FROM employees
WHERE salary>=6000 AND salary<=8000;

SELECT *
FROM employees
WHERE salary>=6000 && salary<=8000;

#  The salary inquiry is not available [6000,8000] Employee information within the scope 
SELECT *
FROM employees
WHERE salary NOT BETWEEN 6000 AND 8000;

SELECT *
FROM employees
WHERE salary<6000 OR salary>8000;

SELECT *
FROM employees
WHERE salary<6000 || salary>8000;

IN() and NOT IN()

#  Inquire about department_id by 10,20,30 Employee information 
SELECT *
FROM employees
WHERE department_id IN (10,20,30);

SELECT *
FROM employees
WHERE department_id=10 OR department_id=20 OR department_id=30;

#  Query salary is not 6000,7000,8000 Employee information 
SELECT *
FROM employees
WHERE salary NOT IN(6000,7000,8000);

SELECT *
FROM employees
WHERE salary<>6000 && salary<>7000 && salary<>8000;

Fuzzy query ：LIKE

#  Inquire about last_name Contains characters 'a' Employee information 
SELECT last_name
FROM employees
WHERE last_name LIKE '%a%';

#  Inquire about last_name In characters 'a' Employee information at the beginning 
SELECT last_name
FROM employees
WHERE last_name LIKE 'a%';

#  Inquire about last_name Contains both characters 'a' Also contains characters 'e' Employee information 
SELECT last_name
FROM employees
WHERE last_name LIKE '%a%' AND last_name LIKE '%e%';

SELECT last_name
FROM employees
WHERE last_name LIKE '%a%e%' OR last_name LIKE '%e%a%';

#  Inquire about last_name The second character is 'a' Employee information 
SELECT last_name
FROM employees
WHERE last_name LIKE '_a%';

Logical operators

Logical operators , Include NOT or !,AND or &&、OR or || 、XOR （ Logical XOR ）.

AND and OR Can be used together , And AND The priority ratio OR High priority .

An operator

An operator , Include ~（ According to the not ）、&（ Bitwise AND ）、|（ Press bit or ）、^（ Bitwise XOR ）、>>（ Right shift to position ）、<<（ Move left according to position ）.