Instance method for mysql string concatenation and setting null value

#String concatenation concat(s1,s2); concatenate the strings in last_name and first_name in the table

select concat(last_name,first_name) as name from employees;

#Only last_name will be modified, not first_name

SELECT first_name,last_name AS f FROM employees;

# Separate the two columns with a comma and name them out_put

SELECT CONCAT(`last_name`,',',`phone_number`) AS out_put FROM employees;

#ifnull determines whether it is empty. If it is empty, it will be displayed as 0 instead of null, and the column name will be displayed as the result

SELECT IFNULL(commission_pct,0) AS result FROM employees;

Content extension:

String concatenation

1.1 The CONCAT(s1, s2, ...) function returns the string generated by concatenating the parameters, one or more contents to be concatenated. If any one of them is NULL, the return value is NULL.

SELECT CONCAT('Current time:',NOW()); -- Output result: Current time: 2019-01-17 11:27:58

1.2 CONCAT_WS(x,s1,s2,...) function

Returns a string consisting of multiple strings concatenated together, with an x ​​between each string.

SELECT CONCAT_WS(';','pan_junbiao's blog','KevinPan','pan_junbiao'); -- Output: pan_junbiao's blog;KevinPan;pan_junbiao

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