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This article mainly explains the "built-in function usage in MySQL". The explanation in the article is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought to study and learn the built-in function usage in MySQL.

Update delete is used in select statements and in the clause where order by hacing

You can use the field name as a field in the function, and the value of the variable is each row of records corresponding to this column.

I. string function

Most of the functions used in mysql are also provided

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1. CONCAT ("string", field, …... .): concatenate the passed parameters into a string, return the concatenated string concat ('adf','bb') and return adfbb

2. INSER (str,x,y,insert): replace the string length y at the beginning of the string str,x position with the string insert

LOWER (str) UPPER (str): converts a string to uppercase or lowercase.

4. LEFT (str,x) RIGHT (str,x): returns the leftmost x characters and the rightmost x characters respectively, and returns null if the second parameter is null

5. LPAD (str,n,pad) RPAD (str,n,pad): populate the leftmost and rightmost str with the string pad until the length is n characters

6. TRIM (str) LTRIM (str) RTRIM (str) / / remove the spaces on both sides of the string, left, and right

7. Replace (str,a,b): replace all occurrence of string an in str with the string b

8. Strcmp (S1 ~ S2): compare ASC size, return-1 if S1 is smaller than S2, return 1 if S1 is larger than S2, and return 0 if S1 equals S2

9. Substring (str,x,y): returns a string of y length from the x-th position in the string str.

Second, numerical function

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ABS (x): returns the absolute value of x

Ceil (x): returns the smallest integer 2.1 2.5 2.9 greater than x and returns the 3-in-1 middle method.

Floor (x); returns the maximum integer less than x 2.1 2.5 2.9 returns 2 rounding

Mod (xPowery): returns the module of xgamy

Rand (): random number between 0-1

Round (xQuery y): returns the value of the parameter x rounded with y decimal places

Truncate (xmemy): returns the result of the number x truncated to y decimal places truncate (1.239Power2) returns 1.23

III. Date function

When using the timestamp of php to complete

Curdate (): returns the date

Now (): returns the date and time

Curtime (): return time

Unix_timestamp (now ()); returns the unix timestamp

From_unixtime (1231314); returns the time of the timestamp

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Week (now ())

Year (now ())

Hour (curtime ())

Minute (curtime ())

Monthname (now ()); month name

Date_format (now (), "% Y-%m-%d% HRV% iRU%")

Fourth, process control function

If (value, tjingf); select if (field > 300) from; return v1 if the condition is true, otherwise return v2

Ifnull (value1,value2) returns value1 if value1 is not empty, value if empty

Case when [value1] then [result]. .. else[default] end

Case when then else end / / select case when salary

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