Zero foundation self-study SQL course | complete collection of SQL basic functions

Hello everyone , I'm Ning Yi .

Today is our first 20 course ：SQL Basic functions .

MySQL There are many functions built in , Used to process values 、 character string 、 Date, etc. , In this lesson, let's talk about some common functions .

1、 Numerical function

-- ROUND( The number , Keep decimals )   rounding 
SELECT ROUND(3.456, 2);  -- 3.46
-- TRUNCATE( The number , Keep decimals )   truncation 
SELECT TRUNCATE(3.456, 2);  -- 3.45
-- CEILING( The number )   The smallest integer greater than or equal to this number 
SELECT CEILING(3.456);  -- 4
-- FLOOR( The number )   The largest integer less than or equal to this number 
SELECT FLOOR(3.456);  -- 3
-- ABS( The number )   The absolute value 
SELECT ABS(-3.456);  -- 3.456
-- RAND()   Random function ,0 To 1 The random value 
SELECT RAND();  -- 0.9206498273840639

2、 String function

-- LENGTH( character string )    String length 
SELECT LENGTH('Cat');  -- 3
-- UPPER( character string )    Turn capitalization 
SELECT UPPER('Cat');  -- 'CAT'
-- LOWER( character string )    Turn lowercase 
SELECT LOWER('Cat');  -- 'cat'
-- TRIM( character string )    Remove the space on both sides 
SELECT TRIM('  Cat  '); -- 'Cat'
-- LTRIM( character string )    Take out the space on the left 
SELECT LTRIM('  Cat  '); -- 'Cat  '
-- RTRIM( character string )     Remove the space on the right 
SELECT RTRIM('  Cat  '); -- '  Cat'
-- LEFT( character string , Character length n)    Take... From the left n Characters 
SELECT LEFT('CatNing', 4); -- 'CatN'
-- RIGHT( character string , Character length n)    Take... From the right n Characters 
SELECT RIGHT('CatNing', 4); -- 'Ning'
-- SUBSTRING( character string , Starting position s, Character length n)    From s Start counting with characters , take n Characters 
--  Here we should pay attention to the separation from other programming languages , Other programming language indexes are mostly from 0 Start , And in the SQL From 1 Start 
SELECT SUBSTRING('CatNing', 3, 4); -- 'tNin'
-- LOCATE( character a, character b)    Positioning characters a In the character b The first place in , If not, return to 0
--  Case insensitive 
SELECT LOCATE('ning', 'CatNing');  -- 4
-- REPLACE( character a, character b, character c)    In the character a in , Use string c Replace string b
--  Case sensitive 
SELECT REPLACE('CatNing', 'Cat', 'Mao'); -- 'MaoNing'
-- CONCAT( character a, character b)    The character a、 character b Splice up 
SELECT CONCAT('Cat', 'Ning'); -- 'CatNing'

Homework ： take Students In the table , The student's name Sname And Student gender Ssex Splice up , Space in the middle , And add a list of random numbers .

Sample results ：

SELECT
  CONCAT(Sname,' ',Ssex) AS " full name   Gender ",
  RAND() AS ' random number '
FROM Students;

Next class we'll talk about MySQL Date function .

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