backtick和单引号之间有什么区别？我可以在上面的查询中使用IF语句吗？ [英] What are the differences between backtick and single quote? Can I use IF statement in a query as above?

问题描述

在代码指示器手册中，写下以下内容。

$ this-> db-> select（）接受一个
可选的第二个参数。如果将
设置为FALSE，CodeIgniter不会尝试
来保护您的字段或表名称
与反引号。如果
需要复合select语句，这将非常有用。

$this->db->select() accepts an optional second parameter. If you set it to FALSE, CodeIgniter will not try to protect your field or table names with backticks. This is useful if you need a compound select statement.

$this->db->select('(SELECT SUM(payments.amount) FROM payments 
WHERE payments.invoice_id=4) AS amount_paid', FALSE);
$query = $this->db->get('mytable');
...

我有以下代码 CI应用程式之一。

$this->db->select('slug, type, 
IF(`value` = "", `default`, `value`) as `value`', FALSE);

Q1。返回引号和单引号之间的区别是什么？

Q1. What are the differences between backtick ` and single quote '?

Q2。我可以在上面的查询中使用IF语句吗？

Q2. Can I use IF statement in a query as above?

Q3。这是什么意思？

Q3. What does this mean?

IF(`value` = "", `default`, `value`) as `value`

推荐答案

1. MySQL，反引号引用名称，而单引号创建字符串。如果你有一个名为的列，选择，当使用没有反引号的名称时，MySQL会抛出一个语法错误，例如 SELECT select FROM foo

1. In MySQL, backticks quote names, while single quotes create strings. If you have a column called select, MySQL would throw an syntax error when using this name without backticks -- like in SELECT select FROM foo -- as it would interpret it as keyword which may not occur there.

可以使用此IF 函数作为SELECT语句中的列规范。请参阅 MySQL参考。

This IF function can be used as a column specification in SELECT statements. See the MySQL reference.

此函数返回默认列中的值，如果 value 是空字符串。否则返回 value 本身的值。结果将被调用 value 。有关详细信息，请参见 MySQL参考。 / p>

This function returns the value from the default column, if value is the empty string. Else it returns the value from value itself. The result will be called value. See the MySQL reference for details.

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