A date function
1, NOW () returns the current date and time
mysql> SELECT NOW(); +---------------------+ | NOW() | +---------------------+ | 2019-10-19 10:55:28 | +---------------------+ 1 row in set (0.00 sec)
2, DATE_FORMAT (d, f) shows the date of the expression f d as required
MySQL > the SELECT the DATE_FORMAT (the NOW (), ' % of the Y -% m Month - Day% d% H:% i points:% s s ' ); + - ----------------------- + -------------------------------------- | the DATE_FORMAT (the NOW (), ' % the Y-years -% m month - day% d% H:% i points:% s s ' ) | + - ------------------------- + ------------------------- | 2019 Nian - October - at 11:00 on the 19th: 03 minutes: 01 seconds | + - --- + ----------------------------------------------- 1 Row in the SET ( 0.00 sec)
3, DATE_ADD (d, INTERVAL expr type) d is calculated by the date after the date of the start of a period of time
mysql> SELECT DATE_ADD(NOW(),INTERVAL 1 DAY); +--------------------------------+ | DATE_ADD(NOW(),INTERVAL 1 DAY) | +--------------------------------+ | 2019-10-20 11:07:47 | +--------------------------------+ 1 row in set (0.00 sec)
Note: \ expr: positive (plus), negative (minus)
\ Unit: support millisecond microsecond, seconds, second, hour hour, day day, week week, in year
Second, String Functions
1, CONCAT (s1, s2 ... sn) String s1, s2, more strings into a string
mysql> SELECT CONCAT('My','SQL'); +--------------------+ | CONCAT('My','SQL') | +--------------------+ | MySQL | +--------------------+ 1 row in set (0.00 sec)
2, FIELD (s, s1, s2 ...) Returns a string s position in the string list (s1, s2 ...) of
mysql> SELECT FIELD('C','A','B','C','D'); +----------------------------+ | FIELD('C','A','B','C','D') | +----------------------------+ | 3 | +----------------------------+ 1 row in set (0.00 sec)
3, LOWER (s) of the string s into all letters lower case letters
mysql> SELECT LOWER('ABCD'); +---------------+ | LOWER('ABCD') | +---------------+ | abcd | +---------------+ 1 row in set (0.00 sec)
4, REVERSE (s) will turn the order of the string s
mysql> SELECT REVERSE('ABCD'); +-----------------+ | REVERSE('ABCD') | +-----------------+ | DCBA | +-----------------+ 1 row in set (0.00 sec)
Third, the digital function
1, ABS (x) returns the absolute value of x
mysql> SELECT ABS(-10); +----------+ | ABS(-10) | +----------+ | 10 | +----------+ 1 row in set (0.00 sec)
2, ROUND (x) returns the nearest integer from x
mysql> SELECT ROUND(1.2345); +---------------+ | ROUND(1.2345) | +---------------+ | 1 | +---------------+ 1 row in set (0.00 sec)
3, RAND () returns a random number between 0 and 1
mysql> SELECT RAND(); +--------------------+ | RAND() | +--------------------+ | 0.5442781900468079 | +--------------------+ 1 row in set (0.00 sec)
4, POW (x, y) returns x to the power y
MySQL > the SELECT the POW ( . 4 , 2 ); # 2. 4 th + - -------- + | the POW ( . 4 , 2 ) | + - -------- + | 16 | + - -------- + 1 Row in the SET ( 0.00 sec)
Fourth, aggregate functions
1, AVG (expression) Returns the average value of an expression, expression is a field
# Return Products table Price field average of MySQL > the SELECT the AVG (. Price) the AS AveragePrice the FROM Products;
2, COUNT (expression) Returns the total number of records query, expression parameter is a field or asterisk
# Return the Products table products field total number of records: MySQL > the SELECT COUNT (the above mentioned id) AS NumberOfProducts the FROM Products;
3, MAX (expression) returns the largest value of the field expression
# Returns the maximum data field in the Products table in Price:
MySQL> the SELECT MAX (Price) the AS LargestPrice the FROM Products;
4, MIN (expression) of the expression returns the minimum field
# Returns the data fields in the Products table minimum Price: MySQL > the SELECT MIN (Price) the AS SmalltPrice the FROM Products;
5, SUM (expression) Returns the specified field sum
Sum # Calculated Cost fields in the Products table: MySQL > the SELECT the SUM (Cost) the AS TotalCost the FROM Products;
6, group_concat (expression) Returns the field contents splicing
MySQL > the SELECT GROUP_CONCAT (name) from crm_product; + - --------------------- + | GROUP_CONCAT (name) | + - ------ + --------------- | iron phosphate lithium battery, the laminated battery | + - --------------------- + 1 Row in the SET ( 0.00 sec)