How to store null in mysql

The NULL value in MySQL represents unknown or non-existent and is stored as a 1-bit bit field flag located at the end of each column data value. This storage scheme efficiently represents NULL values ​​with only 1 bit, allowing fast checking and reducing storage space.

Storage of NULL in MySQL

The meaning of NULL

In MySQL, NULL represents an unknown or non-existent value, the same concept as in the SQL standard.

Storage scheme

MySQL does not store NULL values ​​directly. Instead, it uses a special value to represent NULL, called a bit-field marker (bit-field marker).

bit-field marker is a 1-bit value stored at the end of each column in the table. When the value is 0, it means that the value of the column exists; when the value is 1, it means that the value of the column is NULL.

Storage structure

As shown below, the space allocated for each column contains data values ​​and bit-field markers:

<code>| 数据值 | bit-field marker |</code>

Efficiency Optimization

MySQL uses bit-field marker to represent NULL, which is an efficient storage solution because it:

• Only 1 bit is needed to represent the NULL value
• Allows quick checking of NULL values, only need to check the bit-field marker
• Reduces storage space, because NULL values ​​do not need to store their actual values

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