How to represent non-equal symbols in mysql
Today, I would like to talk to you about how mysql is not equal to symbols, many people may not know much about it. In order to make you understand better, the editor summarized the following content for you. I hope you can get something according to this article.
After testing, it is found that it is possible to use and! = in mysql, but it is not recognized in sqlserver, so it is recommended to use
Selece * from jb51 where id45
The difference between the symbol "! =" in sql
It is not equal to! =, but it is generally used to code because it works in any SQL, but! = is used in sql2000, it is grammatical error and incompatible
The sum in sql is not equal to,'=','! =',','is null'.....
Not equal to:! =, ~ =, ^ = these four symbols are said to be able to express non-equals in oracle, but after trying, it is found that! =, ^ = is OK, ~ = no, it should be noted that only the standard sql syntax is portable, the rest are oracle platform features, portability is poor, so in development, try to use expression is not equal to
Equal to: = needless to say, but to determine the equality of null, you must use is null or is not null,null can only be judged by is null or is not null, other operators and null operations are false.
For example, select * from bl_ip_dt where amount 800. this statement does not find the record where amount equals null
Select * from bl_ip_dt where amount 800or amount is null is OK.
MySql's simple query is not equal to NULL
Query the data in the table where aa is null:
Select * from table where aa is null
Query data in the table where aa is not equal to 1:
Select * from table where aa 1
NULL value operation:
The NULL value can be strange until you get used to it. Conceptually, NULL means "no value" or "unknown value", and it is regarded as a different value. To test NULL, you cannot use arithmetic comparison operators such as =, SELECT 1 = NULL, 1 NULL, 1
< NULL, 1 >NULL
+-+
| | 1 = NULL | 1 NULL | 1 |
< NULL | 1 >NULL |
+-+
| | NULL | NULL | NULL | NULL | |
+-+
Obviously you can't get meaningful results from these comparisons. Instead, use the IS NULL and IS NOT NULL operators:
Mysql > SELECT 1 IS NULL, 1 IS NOT NULL
+-+ +
| | 1 IS NULL | 1 IS NOT NULL |
+-+ +
| | 0 | 1 |
+-+ +
Note that in MySQL, 0 or NULL means false and other values mean true. The default true value for Boolean operations is 1.
Self-perception is null or IFNULL (SUM (), XXX) is often used in development.
In addition, both! and! = can be used in php.
$a = = $b equals TRUE if $an equals $b.
$a = = $b congruent TRUE, if $an equals $b, and they are of the same type. (introduced by PHP 4)
$a! = $b is not equal to TRUE if $an is not equal to $b.
$a $b is not equal to TRUE if $an is not equal to $b.
$a! = $b non-congruent TRUE, if $an is not equal to $b, or they are of different types. (introduced by PHP 4)
$a
< $b 小与 TRUE，如果 $a 严格小于 $b。 $a >$b is greater than TRUE if $an is strict $b.
$a = $b greater than or equal to TRUE, if $an is greater than or equal to $b.
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