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Summary of the most complete MySQL data types in history (Part 2)

2022-07-25 01:12:00 【51CTO】

Then continue to sort out the above , Above we wrote about time type , Then we'll write the date and time type date type .

date type

date Type is used when only date values are required , There is no time part , When storing, you need 3 byte .

The date format is YYYY-MM-DD. among YYYY Indicate year ,MM Represents the month ,DD Means day .

（1） With 'YYYY-MM-DD' perhaps 'YYYYMMDD' Date in string format , The value range is '1000-01-01' ~ '9999-12-3' ; For example, the input '2022-12-31' perhaps ‘20221231’, The date when the database is inserted is 2022-12-31;

（2） With ‘YY-MM-DD’ perhaps ‘YYMMDD’ Date in string format , ad locum ‘YY’ Represents the annual value of two digits . Dates with two digit year values can be confusing , Because I don't know the century .mysql Use the following rules to interpret two digit year values ：‘00~69’ The annual value of the range is converted to 2000-2069,'70-99' The annual value of the range is converted to 1970~1999.

（3） With YY-MM-DD perhaps YYMMDD Date in numeric format , Similar to the front ,00~69 The annual value of the range is converted to 2000～2069,70～99 The annual value of the range is converted to 1970～1999.

（4） Use CURRENT_DATE perhaps NOW(), Insert current system date .

for instance ：

Create a file called yunweijia_4 Data sheet for ;

       
       mysql> create table yunweijia_4 (d date);
       
Query OK, 0 rows affected (0.03 sec)
       
mysql>
      
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Insert some values into the table ;

       
       mysql> insert into yunweijia_4 values ('1999-09-09'), ('19990909'), ('20221010');
       
Query OK, 3 rows affected (0.01 sec)
       
Records: 3  Duplicates: 0  Warnings: 0
       
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Then check the results ：

       
       mysql> select * from yunweijia_4;
       
+------------+
       
| d          |
       
+------------+
       
| 1999-09-09 |
       
| 1999-09-09 |
       
| 2022-10-10 |
       
+------------+
       
3 rows in set (0.00 sec)
       
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Another example ：

Delete data table yunweijia_4 Data in ;

       
       delete from yunweijia_4;
      
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Insert data into the table ;

       
       mysql> insert into yunweijia_4 values ('99-09-09'), ('990909'), ('000101'), ('111111');
       
Query OK, 4 rows affected (0.01 sec)
       
Records: 4  Duplicates: 0  Warnings: 0
       
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Check the results ：

       
       mysql> select * from yunweijia_4;
       
+------------+
       
| d          |
       
+------------+
       
| 1999-09-09 |
       
| 1999-09-09 |
       
| 2000-01-01 |
       
| 2011-11-11 |
       
+------------+
       
4 rows in set (0.00 sec)
       
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Another example ：

Old rules , First delete the data in the table

       
       mysql> delete from yunweijia_4;
       
Query OK, 4 rows affected (0.01 sec)
       
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Insert data into table ;

       
       mysql> insert into yunweijia_4 values (19990909), (990909), (000101), (111111);
       
Query OK, 4 rows affected (0.01 sec)
       
Records: 4  Duplicates: 0  Warnings: 0
       
mysql>
      
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Check the results ：

       
       mysql> select * from yunweijia_4;
       
+------------+
       
| d          |
       
+------------+
       
| 1999-09-09 |
       
| 1999-09-09 |
       
| 2000-01-01 |
       
| 2011-11-11 |
       
+------------+
       
4 rows in set (0.00 sec)
       
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Another example ：

Delete data in table ;

       
       mysql> delete from yunweijia_4;
       
Query OK, 4 rows affected (0.01 sec)
       
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Insert the current time of the system ：

       
       mysql> insert into yunweijia_4 values (current_date()), (now());
       
Query OK, 2 rows affected, 1 warning (0.01 sec)
       
Records: 2  Duplicates: 0  Warnings: 1
       
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View results ：

       
       mysql> select * from yunweijia_4;
       
+------------+
       
| d          |
       
+------------+
       
| 2022-07-09 |
       
| 2022-07-09 |
       
+------------+
       
2 rows in set (0.00 sec)
       
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CURRENT_DATE Only the current date value is returned , Not including the time part ;NOW() Function returns date and time values , When saving to the database , Only the date part is retained .

datetime type

DATETIME Type is used for values that need to contain both date and time information , When storing, you need 8 byte . The date format is ‘YYYY-MM-DD HH:MM:SS’. among ,YYYY Indicate year ,MM Represents the month ,DD Means day ,HH For hours ,MM Represents minutes ,SS For seconds . In giving DATETIME When assigning a field of type , You can insert data using either a string type or a number type , As long as meet DATETIME The date format can be .

（1） With ‘YYYY-MM-DD HH:MM:SS’ perhaps ‘YYYYMMDDHHMMSS’ Value in string format , The value range is ‘1000-01-01 00:00:00’～‘9999-12-3 23:59:59’;

（2） With ‘YY-MM-DD HH:MM:SS’ perhaps ‘YYMMDDHHMMSS’ Date in string format , ad locum YY Represents the annual value of two digits . Same as before ,‘00～69’ The annual value of the range is converted to ‘2000～2069’,‘70～99’ The annual value of the range is converted to ‘1970～1999’.

（3） With YYYYMMDDHHMMSS perhaps YYMMDDHHMMSS Date and time in numeric format .

TIMESTAMP type

TIMESTAMP The display format is the same as DATETIME identical , The display width is fixed at 19 Characters , The date format is YYYY-MM-DD HH:MM:SS, When storing, you need 4 byte .TIMESTAMP The value range of column is less than DATETIME Value range of , by ‘1970-01-01 00:00:01’UTC～‘2038-01-1903:14:07’UTC. among ,UTC（Coordinated Universal Time） For world standard time , So when inserting data , Ensure that it is within the legal value range .

Be careful ：

because datetime The type and TIMESTAMP It is quite different from the above usage , So here are no more examples .

Text string type

The string type is used to store string data , In addition to storing string data , Other data can also be stored , Such as binary data of pictures and sounds .

mysql Support two types of string data ： Text strings and binary strings ;

Text strings can be used for case sensitive or case insensitive string comparison , You can also search for pattern matching .

stay mysql in , The text string type refers to ：

CHAR
VARCHAR
TEXT
ENUM
SET

See the following table for details ：

The most complete in history mysql Data type summary （ Next ）_ character string

VARCHAR and TEXT The type and BLOB All are Variable length type , Its storage requirements Depends on the actual length of the column value （ Use... In the previous table L Express ）, Rather than depending on the maximum possible size of the type .

for example , One VARCHAR(10) The maximum length that the column can save is 10 Character string , The actual storage needs to be the length of the string L add 1 byte （ Record the length of the string ）. For characters “abcd”,L yes 4 The storage requirements are 5 byte .

CHAR and VARCHAR type

CHAR(M) Is a fixed length string , Specify the string column length when defining . Fill in the space on the right when saving , To reach the specified length .M Column length ,M The range is 0~255 Characters .

for example ：CAHR(4) Defines a fixed length character string , The maximum number of characters it contains is 4. When the retrieved CHAR When the value of , The trailing space will be deleted .

VARCHAR(M) Is a variable length string ,M Indicates the maximum column length .M The range is 0~65535.VARCHAR The maximum actual length of is determined by the size of the longest line and the character set used , The actual space occupied is the actual length of the string plus 1.

for example ：VARCAHR(50) Defines a maximum length of 50 String , If the inserted string is only 10 Characters , Then the actual stored string is 10 Characters and a string ending character .VARCHAR When the corresponding value is saved and retrieved, the trailing space remains .

Let's take a look at CHAR(4) and VARCHAR(4) What is the difference between storage ：

The most complete in history mysql Data type summary （ Next ）_mysql_02

We can see from the comparison results in the above figure ,CHAR(4) The fixed length is defined as 4 The column of , No matter how long the stored data is , The space occupied is 4 Bytes ;VARCHAR(4) The number of bytes occupied by the defined column is the actual length plus 1;

But the query is different , We can look at it through the following example ;

for instance ：

Create a file called yunweijia_5 Data sheet for ;

       
       mysql> create table yunweijia_5 (ch char(4), var varchar(4));
       
Query OK, 0 rows affected (0.03 sec)
       
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Insert some data into this data table ;

       
       mysql> insert into yunweijia_5 values ('ab', 'ab');
       
Query OK, 1 row affected (0.01 sec)
       
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Check the results ：

       
       mysql> select concat ('(', ch, ')'), concat ('(', var, ')') from yunweijia_5;
       
+-----------------------+------------------------+
       
| concat ('(', ch, ')') | concat ('(', var, ')') |
       
+-----------------------+------------------------+
       
| (abc)                 | (abc)                  |
       
+-----------------------+------------------------+
       
1 row in set (0.00 sec)
       
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There's a problem here , The document above describes ,char The space will be deleted when saving ,varchar The space at the end will be reserved , But from the perspective of its own practice , Whether it's char still varchar Have deleted the space at the end .

TEXT type

TEXT Column holds non binary strings , Such as the content of the article 、 Comments, etc .

When saving or querying TEXT Column value , Do not delete trailing spaces .

Text Types are divided into 4 Kind of ：

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