$strcasecmp (expression operator)（表达式运算符）

Definition定义

$strcasecmp

Performs case-insensitive comparison of two strings. Returns对两个字符串执行不区分大小写的比较。返回

• 1 if first string is "greater than" the second string.如果第一个字符串“大于”第二个字符串，则为1。
• 0 if the two strings are equal.如果两个字符串相等，则为0。
• -1 if the first string is "less than" the second string.如果第一个字符串“小于”第二个字符串，则为-1。

$strcasecmp has the following syntax:具有以下语法：

{ $strcasecmp: [ <expression1>, <expression2> ] }

The arguments can be any valid expression as long as they resolve to strings. 参数可以是任何有效的表达式，只要它们解析为字符串即可。For more information on expressions, see Expressions.有关表达式的详细信息，请参阅表达式。

Behavior行为

$strcasecmp only has a well-defined behavior for strings of ASCII characters.仅对ASCII字符串具有明确定义的行为。

For a case sensitive comparison, see $cmp.有关区分大小写的比较，请参阅$cmp。

Example示例

Consider a inventory collection with the following documents:考虑使用以下文件进行inventory集合：

db.inventory.insertMany( [
   { _id: 1, item: "ABC1", quarter: "13Q1", description: "product 1" },
   { _id: 2, item: "ABC2", quarter: "13Q4", description: "product 2" },
   { _id: 3, item: "XYZ1", quarter: "14Q2", description: null }
] )

The following operation uses the $strcasecmp operator to perform case-insensitive comparison of the quarter field value to the string "13q4":以下操作使用$strcasecmp运算符对quarter字段值与字符串"13q4"进行不区分大小写的比较：

db.inventory.aggregate(
   [
     {
       $project:
          {
            item: 1,
            comparisonResult: { $strcasecmp: [ "$quarter", "13q4" ] }
          }
      }
   ]
)

The operation returns the following results:该操作返回以下结果：

{ _id: 1, item: "ABC1", comparisonResult: -1 }
{ _id: 2, item: "ABC2", comparisonResult: 0 }
{ _id: 3, item: "XYZ1", comparisonResult: 1 }