“其中1 = 1”声明 [英] "where 1=1" statement

问题描述

可能重复：

我看到一些人使用语句查询在MySQL数据库中的表如下：

I saw some people use a statement to query a table in a MySQL database like the following:

select * from car_table where 1=1 and value="TOYOTA"

但是 1 = 1 p>

But what does 1=1 mean here?

推荐答案

通常当人们建立SQL语句时。

It's usually when folks build up SQL statements.

和value =Toyota你不必担心是否有条件或只是WHERE。优化器应该忽略它。

When you add and value = "Toyota" you don't have to worry about whether there is a condition before or just WHERE. The optimiser should ignore it

没有魔法，只是实用

Example Code：

Example Code:

commandText = "select * from car_table where 1=1";

if (modelYear <> 0)     commandText += " and year="+modelYear
if (manufacturer <> "") commandText += " and value="+QuotedStr(manufacturer)
if (color <> "")        commandText += " and color="+QuotedStr(color)
if (california)         commandText += " and hasCatalytic=1"

否则你必须有一组复杂的逻辑：

Otherwise you would have to have a complicated set of logic:

commandText = "select * from car_table"
whereClause = "";
if (modelYear <> 0)
{
   if (whereClause <> "") 
      whereClause = whereClause + " and ";
   commandText += "year="+modelYear;
}
if (manufacturer <> "")
{    
   if (whereClause <> "") 
      whereClause = whereClause + " and ";
   commandText += "value="+QuotedStr(manufacturer)
}
if (color <> "")
{
   if (whereClause <> "") 
      whereClause = whereClause + " and ";
   commandText += "color="+QuotedStr(color)
}
if (california)
{
   if (whereClause <> "") 
      whereClause = whereClause + " and ";
   commandText += "hasCatalytic=1"
}

if (whereClause <> "")
   commandText = commandText + "WHERE "+whereClause;

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