mysql if not equal to
The use of IF function in MySQL for conditional judgment is common in query operations. The IF function can return different results based on certain conditions. A common usage is to use the IF function in a SELECT statement, but it can also be used in INSERT, UPDATE, and DELETE statements.
The IF function accepts three parameters. The first parameter is the condition to be judged. The second parameter is the value returned when the condition is true. The third parameter is the value returned when the condition is false. The syntax of the IF function is as follows:
IF(condition, true_value, false_value)
Among them, condition is the condition to be judged. If the condition is true, true_value is returned, otherwise false_value is returned.
There are many ways to perform conditional judgment in MySQL, the common ones are IF and CASE WHEN statements. IF is often used to determine whether a value is equal to another value. For example:
SELECT IF(column_name = 'value', 'true_value', 'false_value') FROM table_name;
This statement will retrieve the row with column_name as 'value' in the table_name table. If found, it will return 'true_value', otherwise it will return ' false_value'.
But what if we want to perform a non-equal comparison? In MySQL, unequal comparisons use the != or <> operators. For example:
SELECT IF(column_name != 'value', 'true_value', 'false_value') FROM table_name;
This statement will search the table_name table for rows whose column_name is not 'value'. If found, it will return 'true_value', otherwise it will return 'false_value'.
In addition to using the IF function, we can also use the CASE WHEN statement for conditional judgment. The CASE WHEN statement is a SQL standard statement and is also widely used in MySQL. The syntax is as follows:
CASE
WHEN condition1 THEN result1
WHEN condition2 THEN result2
ELSE result3
END
Among them, condition1 and condition2 are the two conditions to be judged. If the condition is true, the corresponding result1 and result2 are returned. If none of the conditions are true, result3 is returned.
For example, if we want to retrieve rows in the table_name table where column_name is not 'value', we can use the following statement:
SELECT
CASE
WHEN column_name <> 'value' THEN 'true_value'
ELSE 'false_value'
END AS result
FROM table_name;
This statement will also retrieve rows in the table_name table where column_name is not 'value' ' line, if found, returns 'true_value', otherwise returns 'false_value'.
In summary, you can use the != or <> operator for unequal comparison in MySQL, and you can also use the IF function and CASE WHEN statement for conditional judgment. In practical applications, we can choose different methods according to different needs to get the most appropriate results.
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