How to solve mysql if then error

The if-then statement in MySQL is usually used to implement conditional control. Its basic format is as follows:

IF condition THEN
    statement_list
END IF

Among them, condition is a logical expression. If the expression is true, the statement in statement_list will be executed, otherwise it will not be executed.

However, when using if-then statements, we need to pay attention to some details. Below, I will introduce several situations in which errors may occur and provide corresponding solutions.

1. The wrong operator is used in the conditional expression

Using the wrong operator in the conditional expression will cause problems with the if-then statement. For example, if bit operators (&, |, ^, etc.) or string concatenation operators (||) are used in conditional expressions, the following error will occur:

mysql> IF (1|1) THEN SELECT 'TRUE' ELSE SELECT 'FALSE' END IF;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '|1) THEN SELECT 'TRUE' ELSE SELECT 'FALSE' at line 1

Solution: Check the conditional expression Whether the correct operator is used in the formula, if it is wrong, it should be modified to the correct operator.

2. There is a syntax error in the conditional expression

If there is a syntax error in the conditional expression, it will result in an error in the if-then statement.. For example, if parentheses or quotation marks are missing in the conditional expression, the following error will occur:

mysql> IF str = 'hello' THEN SELECT 'TRUE' ELSE SELECT 'FALSE' END IF;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '= 'hello' THEN SELECT 'TRUE' ELSE SELECT 'FALSE' at line 1

Solution: Check whether there are syntax errors in the conditional expression and correct it accordingly.

3. IF statement format error

When using if-then statements, if the format is incorrect, it will also cause statement errors. If the END IF statement is missing or the space between the IF statement and the SELECT statement is omitted, the following error will occur:

mysql> IF (1=1) THEN SELECT 'TRUE' ELSE SELECT 'FALSE'
    -> ;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'ELSE SELECT 'FALSE'' at line 1

Solution: Check whether the format of the IF statement is correct, use the END IF statement correctly, and Add a space between the IF statement and the following SELECT statement.

4. The output result of the conditional expression is empty

The IF statement may cause an error because the output result of the conditional expression may be empty. When the variables in the conditional expression are not defined or their value is NULL, the following error will result

mysql> IF (a = 1) THEN SELECT 'TRUE' ELSE SELECT 'FALSE' END IF;
ERROR 1048 (23000): Column 'a' cannot be null

Solution: Make sure the variables in the conditional expression have been correctly defined and are not NULL.

The above is the detailed content of How to solve mysql if then error. For more information, please follow other related articles on the PHP Chinese website!