mysql IFNULL ELSE
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mysql IFNULL ELSE
提问by mcgrailm
I have a select statement where I want to make select conditional like this
我有一个 select 语句，我想像这样使 select 有条件
IFNULL(field_a,field_a,feild_b)
so that it checks field a if a is null then the select would be field b
以便它检查字段 a 如果 a 为空，则选择将是字段 b
is that possible ?
那可能吗 ？
回答by OMG Ponies
Use COALESCE:
使用合并：
SELECT COALESCE(field_a, field_b)
COALESCE is an ANSI standard function that returns the first non-null value from the list of columns specified, processing the columns from left to right. So in the example, if field_ais null, field_bvalue will be displayed. However, this function will return NULL if there is no non-null value from the columns specified.
COALESCE 是一个 ANSI 标准函数，它返回指定列列表中的第一个非空值，从左到右处理列。所以在示例中，如果field_a为空，field_b则将显示值。但是，如果指定的列中没有非空值，则此函数将返回 NULL。
It's supported on MySQL (I've used it on 4.1), SQL Server (since v2000), Oracle 9i+...
它支持 MySQL（我在 4.1 上使用过）、SQL Server（自 v2000 起）、Oracle 9i+...
回答by user3590489
and another way to skin that cat (flexible for not just null comparisons)...
以及另一种给那只猫剥皮的方法（不仅适用于空比较灵活）...
select if(field_a is not null, field_a, field_b) from...
回答by Matt
回答by Developer
MySQL IFNULL() With Syntax & Examples
MySQL IFNULL() 带语法和示例
Syntax
句法
The syntax of the IFNULL function is:
IFNULL 函数的语法是：
IFNULL(expression_1,expression_2);
SELECT
name, IFNULL(businessphone, homephone) phone
FROM
users;
#The above query return this result from users table
+------------+-----------+----------+-----------
| id | name | phone |
+------------+-----------+----------+-----------
| 5 | Tommy Hill | (541) 754-3009 |
| 6 | John Smith | (541) 754-3110 |
| 10 | Mark Greenspan | (541) 754-3111 |
| 11 | Kelvin Row | (541) 754-3111 |
+------------+-----------+----------+-----------
