MySQL Where Condition Statement Introduction and operator summary _mysql

WHERE condition

Sometimes when you manipulate a database, you manipulate only conditionally restricted data, and you can add a WHERE clause to the SQL statement to specify the conditions for the operation of the data.

Grammar:

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SELECT column,... From Tb_name WHERE definition

The WHERE keyword is followed by a valid expression (definition) that represents the condition that the data record being manipulated must meet.
In addition to SELECT, the WHERE condition keyword can be used in any situation that the SQL syntax allows, such as update (update), delete (delete), and so on.
Example:

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SELECT * FROM user WHERE username = ' Jack '

This example specifies that the query condition is username equal to Jack's data.

Operator description in WHERE expression:

Parameter description:

operator	Description
=	Equals
!=	Not equal to, some database systems also write <>
>	Greater than
<	Less than
>=	Greater than or equal to
<=	Less than or equal to
BETWEEN ... And ...	Within a range, example: WHERE age BETWEEN 30
Not BETWEEN ... And ...	Not within a certain range
In (item 1, item 2,...)	Within the specified item, example: Where City in (' Beijing ', ' Shanghai ')
Not in (item 1, item 2,...)	is not in the specified item
Like	Search matches, often used in conjunction with pattern matching characters
Not like	The anti-righteousness of like
Is NULL	Null-value-judging character
is not NULL	Non-null Judge character
Not, and, or	Logical operators that represent no, and, or, for multiple logical connections. Priority: not > and > OR
%	pattern-matching character, representing any string, example: WHERE username like '%user '

Some WHERE examples

To specify a user based on user name query:

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SELECT * FROM user WHERE username = ' Jack '

Check the name and ID number of the user registered after 0 o'clock in the morning January 1, 2009:

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$regdate = Mktime (00, 00, 01, 01, 01, 2009);
SELECT uid,username from user WHERE regdate >= $regdate

Search for all users in the username with the word User:

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SELECT * FROM user WHERE username like '%user% '

Search for all users in the username that contain user or admin:

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SELECT * FROM user WHERE username like '%user% ' OR username like '%admin% '